Jetpack Compose, the modern Android UI toolkit, has revolutionized how we build user interfaces. With its declarative approach, Compose simplifies UI development and makes it more intuitive. One of the exciting aspects of Compose is its built-in animation capabilities. In this blog post, we’ll explore how to create engaging animations using Jetpack Compose.
Animate Common Composable Properties
Compose provides convenient APIs for animating common properties of a composable. Let’s dive into some examples:
1. Animating Visibility
You can use AnimatedVisibility to hide or show a composable. Here’s a basic example:var visible by remember { mutableStateOf(true) } AnimatedVisibility(visible) { // Your composable here // ... }
The enter and exit parameters of AnimatedVisibility allow you to configure how a composable behaves when it appears and disappears. Alternatively, you can animate the alpha over time using animateFloatAsState:val animatedAlpha by animateFloatAsState( targetValue = if (visible) 1.0f else 0f, label = "alpha" ) Box( modifier = Modifier .size(200.dp) .graphicsLayer { alpha = animatedAlpha } .clip(RoundedCornerShape(8.dp)) .background(colorGreen) .align(Alignment.TopCenter) ) { // Your content here }
Keep in mind that changing the alpha keeps the composable in the composition, whereas AnimatedVisibility eventually removes it.
2. Animating Background Color
To animate the background color of a composable, use animateColorAsState:val animatedColor by animateColorAsState( if (animateBackgroundColor) colorGreen else colorBlue, label = "color" ) Column( modifier = Modifier.drawBehind { drawRect(animatedColor) } ) { // Your composable here }
This approach is more performant than using Modifier.background(), especially when animating colors over time.
Practical Magic with Animations
Compose offers many other animation mechanisms, such as animating size, position, and more. For a comprehensive understanding, explore the full set of API options in the Compose Animation documentation.
In summary, Jetpack Compose empowers developers to create delightful and interactive UIs with ease. Whether you’re building a simple app or a complex interface, animations play a crucial role in enhancing the user experience. Happy animating! 🚀
Source: Conversation with Bing, 3/24/2024 (1) Quick guide to Animations in Compose | Jetpack Compose | Android Developers. https://developer.android.com/jetpack/compose/animation/quick-guide. (2) Quick Start Guide on Animations in Jetpack Compose – Finotes Blog. https://www.blog.finotes.com/post/quick-start-guide-on-animations-in-jetpack-compose. (3) Animate Your Jetpack Compose UI: A Comprehensive Overview. https://blog.realogs.in/animating-jetpack-compose-ui/. (4) Jetpack compose: Custom animations | by Hardik P | Canopas. https://blog.canopas.com/jetpack-compose-custom-animations-550dcdcded83. (5) Animations in Jetpack Compose: animateContentSize – Medium. https://medium.com/@timacosta06/animations-in-compose-animatecontentsize-1eca1194ca1e.
Let’s dive into the world of Jetpack Compose and explore how to use LazyColumn effectively. 🚀
Introduction
Jetpack Compose is a modern Android UI toolkit that simplifies building native user interfaces. One of its powerful features is the LazyColumn, which provides an efficient way to display large lists. Think of it as the successor to the good old RecyclerView and its adapter.
In this blog post, we’ll explore what LazyColumn is, how it works, and how you can leverage it to create dynamic and performant lists in your Android apps.
What is LazyColumn?
LazyColumn is a vertically scrolling list that only composes and lays out the currently visible items. Unlike a regular Column, which renders all items regardless of visibility, LazyColumn is “lazy.” It means that it efficiently handles large lists by rendering only the items currently visible on the screen. This lazy behavior significantly improves performance when dealing with extensive datasets.
Basic Usage
Let’s get started with some code examples. Suppose you want to create a simple list of messages using LazyColumn. Here’s how you can do it:@Composable fun MessageList(messages: List<Message>) { LazyColumn { items(messages) { message -> MessageRow(message) } } }
In the above snippet:
We define a MessageList composable that takes a list of Message objects.
Inside the LazyColumn block, we use the items function to iterate over the messages and compose each MessageRow.
DSL for Describing Items
The magic of LazyColumn lies in its DSL (domain-specific language). Instead of directly emitting composables like in a regular Column, we work with a LazyListScope block. This scope allows us to describe the item contents efficiently.
Adding Single Items
The most basic function in the DSL is item(), which adds a single item:LazyColumn { item { Text(text = "First item") } items(5) { index -> Text(text = "Item: $index") } item { Text(text = "Last item") } }
Handling Collections
We can also add collections of items using extensions like items() or itemsIndexed():LazyColumn { items(messages) { message -> MessageRow(message) } }
The itemsIndexed() extension even provides the index for more advanced scenarios.
Conclusion
And there you have it! LazyColumn is your go-to solution for efficiently displaying lists in Jetpack Compose. Whether you’re building a chat app, a news feed, or any other data-driven UI, give LazyColumn a try.
Remember, it’s all about being lazy in the right way—rendering only what’s necessary and keeping your UI smooth and responsive. Happy composing! 🎨
Source: Conversation with Bing, 3/23/2024 (1) Jetpack Compose | Implementing a LazyColumn / RecyclerView | Part I. https://www.youtube.com/watch?v=_G0ndJLbaJI. (2) How to Create a Lazy Column With Categories in Jetpack Compose. https://www.youtube.com/watch?v=XfYlRn_Jy1g. (3) How to Implement a Multi-Select LazyColumn in Jetpack Compose – Android Studio Tutorial. https://www.youtube.com/watch?v=pvNcJXprrKM. (4) Lists and grids | Jetpack Compose | Android Developers. https://developer.android.com/jetpack/compose/lists. (5) LazyColumn in Jetpack Compose – Jetpack Compose World. https://jetpackcomposeworld.com/lazycolumn-in-jetpack-compose/. (6) Column vs LazyColumn in Android Jetpack Compose. https://codingwithrashid.com/column-vs-lazycolumn-in-android-jetpack-compose/. (7) LazyColumn – Jetpack Compose Playground – GitHub Pages. https://foso.github.io/Jetpack-Compose-Playground/foundation/lazycolumn/. (8) undefined. https://pl-coding.com/premium-courses/.
Let’s delve into the world of MVVM (Model-View-ViewModel) architecture and explore its advantages. 🚀
Understanding MVVM Architecture
MVVM is a software design pattern that cleanly separates the graphical user interface (View) from the business logic (Model) of an application. It was invented by Microsoft architects Ken Cooper and Ted Peters. The ultimate goal of MVVM is to make the view completely independent from the application logic. Here are the key components of MVVM:
Model: Represents the app’s domain model, including data models, business logic, and validation rules. It communicates with the ViewModel and remains unaware of the View.
View: Represents the user interface of the application. It holds limited, purely presentational logic and is completely agnostic to the business logic. The View communicates with the ViewModel through data binding.
ViewModel: Acts as the link between the View and the Model. It exposes public properties and commands that the View uses via data binding. When state changes occur, the ViewModel notifies the View through notification events.
Advantages of MVVM
Easier Development:
Separating the View from the logic allows different teams to work on different aspects of the application simultaneously.
Developers can focus on their specific areas (View, ViewModel, or Model) without stepping on each other’s toes.
Easier Testing:
UI testing is notoriously challenging. MVVM simplifies this by isolating the business logic in the ViewModel.
Unit testing the ViewModel becomes straightforward, as it doesn’t rely on UI components.
Improved Maintainability:
The separation between View and ViewModel makes code maintenance more manageable.
Changes to the UI (View) won’t impact the underlying logic (ViewModel).
Code Reusability:
ViewModel logic can be reused across different Views.
For example, if you have similar functionality in multiple screens, you can share the ViewModel code.
Parallel Development:
MVVM allows parallel development by enabling different teams to work on different layers.
UI designers can focus on the View, while developers handle the ViewModel and Model.
MVVM vs. Other Architectures
MVC (Model-View-Controller): MVVM evolved from MVC. While MVC separates applications into three components (Model, View, and Controller), MVVM replaces the Controller with the ViewModel. MVVM aims to minimize code-behind logic in the View.
Two-Way Communication: Unlike MVC’s one-way communication (Controller to View), MVVM enables two-way communication between View and ViewModel through data binding.
In summary, MVVM provides a clear separation of concerns, improves maintainability, and enhances testability. It’s a powerful pattern for building robust and scalable applications. So, next time you’re architecting your app, consider embracing MVVM! 🌟
Source: Conversation with Bing, 2/26/2024 (1) What Is MVVM Architecture? (Definition, Advantages) | Built In. https://builtin.com/software-engineering-perspectives/mvvm-architecture. (2) Understanding MVVM Architecture in Android – Medium. https://medium.com/swlh/understanding-mvvm-architecture-in-android-aa66f7e1a70b. (3) Mastering MVVM: A Comprehensive Guide to the Model-View-ViewModel …. https://dev.to/mochafreddo/mastering-mvvm-a-comprehensive-guide-to-the-model-view-viewmodel-architecture-221g. (4) Understanding MVVM architecture for Beginners | by Rosh | Medium. https://medium.com/@rosh_dev/understanding-mvvm-architecture-for-beginners-586caaa72179. (5) Why MVVM and what are it’s core benefits? – Stack Overflow. https://stackoverflow.com/questions/1644453/why-mvvm-and-what-are-its-core-benefits.
Let’s dive into how you can integrate Detekt into your Android Studio projects to improve code quality. Detekt is a powerful static code analysis tool for Kotlin that helps identify code smells and enforce best practices. Here’s a step-by-step guide:
Integrating Detekt in Android Studio Projects
1. Understanding Detekt
Detekt is designed to enhance your codebase by enforcing a set of rules. It’s particularly useful when collaborating with a team of developers. Some key features of Detekt include:
Code Smell Analysis: Detekt identifies potential code smells in your Kotlin projects.
Highly Configurable: You can customize Detekt according to your specific needs.
Suppression Options: Suppress findings if you don’t want warnings for everything.
IDE Integration: Detekt integrates seamlessly with Android Studio.
Thresholds and Baselines: Specify code-smell thresholds to break builds or print warnings.
2. Adding Detekt to Your Project
To integrate Detekt into your Android project, follow these steps:
Open Android Studio and sync your project with the Gradle files.
Add Detekt Gradle Plugin: In your project’s build.gradle file, add the Detekt Gradle plugin as a dependency. For example: gradle plugins { id("io.gitlab.arturbosch.detekt") version "1.18.1" }
Run Detekt: Open the terminal in Android Studio and execute the following command: ./gradlew detekt Detekt will analyze your code, identify issues, and provide details on what needs improvement.
3. Rule Sets in Detekt
Detekt comes with predefined rule sets that check compliance with your code. These rules focus on improving code quality without affecting your app’s functionality. Here are some common rule sets:
Comments: Addresses issues in comments and documentation.
Complexity: Reports complex code, long methods, and parameter lists.
Naming: Enforces naming conventions for classes, packages, functions, and variables.
Remember that Detekt is highly configurable, so you can tailor it to your project’s specific needs.
4. Custom Rules and Processors
Detekt allows you to add your own custom rules and processors. If you encounter specific patterns or code smells unique to your project, consider creating custom rules to catch them.
Conclusion
By integrating Detekt into your Android Studio projects, you’ll proactively identify code issues, maintain consistent code quality, and collaborate effectively with your team. Happy coding! 🚀
I hope you find this guide helpful! If you have any further questions or need additional assistance, feel free to ask. 😊
Source: Conversation with Bing, 2/15/2024 (1) Integrating detekt in the Android Studio | by Nagendran P | Medium. https://medium.com/@nagendran.p/integrating-detekt-in-the-android-studio-442128e971f8. (2) Integrating detekt in the Workflow | Kodeco. https://www.kodeco.com/24470020-integrating-detekt-in-the-workflow. (3) How to Analyze Your Code with Detekt | by Maria Luíza – Medium. https://medium.com/mobile-app-development-publication/how-analyze-your-code-with-detekt-37be6c9c9105. (4) detekt – IntelliJ IDEs Plugin | Marketplace – JetBrains Marketplace. https://plugins.jetbrains.com/plugin/10761-detekt. (5) How to use detekt on a daily basis (in a multi module Android project …. https://proandroiddev.com/how-to-use-detekt-in-a-multi-module-android-project-6781937fbef2. (6) undefined. https://detekt.github.io/detekt/configurations.html%29. (7) Improve Code Quality Using Static Code Analysis With detekt. https://williamkingsley.medium.com/improve-code-quality-with-static-code-analysis-using-detekt-454b7e66d2ec. (8) Adding Detekt to your Android project – Since Last Commit. https://blog.asadmansoor.com/adding-detekt-to-your-android-project/.
Kotlin is a modern programming language that offers many features to make coding easier and more enjoyable. One of these features is the ability to extend a class or an interface with new functionality without having to inherit from it or use design patterns such as Decorator. This is done via special declarations called extension functions.
Extension functions are useful when you want to add some functionality to a class that you can’t modify, such as a class from a third-party library. For example, you can write new functions for the String class that can be used as if they were methods of the String class.
In this blog post, we will explore some common extension functions that are available in Kotlin for the String class. We will also see how to write our own extension functions and how they are resolved at compile-time.
Built-in Extension Functions for String Class
The String class in Kotlin comes with a huge number of extension functions that can make working with strings easier and more concise. Here are some examples of these functions:
replace(oldChar: Char, newChar: Char, ignoreCase: Boolean = false): String – This function returns a new string with all the occurrences of the oldChar replaced with newChar. The ignoreCase parameter is false by default. If set to true, it will ignore case while handling the replacement. For example:
uppercase(): String – This function returns a new string with all the characters converted to uppercase. For example:
val inputString = "hello" println(inputString.uppercase()) // HELLO
lowercase(): String – This function returns a new string with all the characters converted to lowercase. For example:
val inputString = "HELLO" println(inputString.lowercase()) // hello
toCharArray(): CharArray – This function returns a char array containing the characters of the string. For example:
val inputString = "hello" val charArray = inputString.toCharArray() println(charArray.joinToString()) // h, e, l, l, o
substring(startIndex: Int, endIndex: Int): String – This function returns a new string that is a substring of the original string starting from startIndex (inclusive) and ending at endIndex (exclusive). For example:
val inputString = "hello" println(inputString.substring(1, 4)) // ell
startsWith(prefix: String, ignoreCase: Boolean = false): Boolean – This function returns true if the string starts with the specified prefix. The ignoreCase parameter is false by default. If set to true, it will ignore case while checking for the prefix. For example:
endsWith(suffix: String, ignoreCase: Boolean = false): Boolean – This function returns true if the string ends with the specified suffix. The ignoreCase parameter is false by default. If set to true, it will ignore case while checking for the suffix. For example:
compareTo(other: String, ignoreCase: Boolean = false): Int – This function compares the string with another string lexicographically and returns an integer value. The value is negative if the string is less than the other string, zero if they are equal, and positive if the string is greater than the other string. The ignoreCase parameter is false by default. If set to true, it will ignore case while comparing the strings. For example:
There are many more extension functions for the String class in Kotlin that you can explore in the official documentation.
Writing Your Own Extension Functions for String Class
You can also write your own extension functions for the String class or any other class in Kotlin. To declare an extension function, you need to prefix its name with a receiver type, which refers to the type being extended. For example, the following adds a reverse() function to the String class:
fun String.reverse(): String { return this.reversed() }
The this keyword inside an extension function corresponds to the receiver object (the one that is passed before the dot). Now, you can call such a function on any String object in Kotlin:
val inputString = "hello" println(inputString.reverse()) // olleh
You can also make your extension functions generic by declaring the type parameter before the function name. For example, the following adds a swap() function to the MutableList class that can swap two elements of any type:
fun <T> MutableList<T>.swap(index1: Int, index2: Int) { val tmp = this[index1] this[index1] = this[index2] this[index2] = tmp } val list = mutableListOf(1, 2, 3) list.swap(0, 2) println(list) // [3, 2, 1]
How Extension Functions Are Resolved
It is important to understand that extension functions do not actually modify the classes they extend. They are just syntactic sugar that allows you to call new functions with the dot-notation on variables of that type. Extension functions are resolved statically at compile-time, which means they are not virtual by receiver type. The extension function being called is determined by the type of the expression on which the function is invoked, not by the type of the result from evaluating that expression at runtime.
For example, consider the following code:
open class Shape class Rectangle: Shape() fun Shape.getName() = "Shape" fun Rectangle.getName() = "Rectangle" fun printClassName(s: Shape) { println(s.getName()) } printClassName(Rectangle())
This code prints Shape, because the extension function called depends only on the declared type of the parameter s, which is the Shape class. The actual type of s at runtime (Rectangle) does not matter.
If a class has a member function with the same name and signature as an extension function, the member always wins. For example:
class Example { fun printFunctionType() { println("Class method") } } fun Example.printFunctionType() { println("Extension function") } Example().printFunctionType() // Class method
This code prints Class method, because the member function of the Example class overrides the extension function.
Conclusion
In this blog post, we have learned about some common extension functions for the String class in Kotlin and how to write our own extension functions for any class. We have also seen how extension functions are resolved at compile-time and how they do not modify the classes they extend.
Extension functions are a powerful feature of Kotlin that can help you write more concise and expressive code. They can also help you extend existing classes with new functionality without having to inherit from them or use design patterns such as Decorator.
If you want to learn more about extension functions and other features of Kotlin, you can check out these resources:
Variance is a concept that describes how types relate to each other when they have type parameters. For example, if Dog is a subtype of Animal, is List<Dog> a subtype of List<Animal>? The answer depends on the variance of the type parameter of List.
In this blog, we will explore the different kinds of variance in Kotlin and how they affect the type system and the code we write. We will also compare them with Java’s wildcard types and see how Kotlin simplifies the syntax and semantics of generics.
Declaration-site variance
One way to achieve variance in Kotlin is by using declaration-site variance. This means that we can specify the variance of a type parameter at the class level, where it is declared. This affects all the members and fields of the class that use that type parameter.
For example, let’s define a simple class that represents a producer of some type T:
class Producer<T>(val value: T) { fun produce(): T = value }
This class has a type parameter T that appears as the return type of the produce() method. Now, let’s say we have two subtypes of Animal: Dog and Cat. We can create instances of Producer<Dog> and Producer<Cat>:
val dogProducer = Producer(Dog()) val catProducer = Producer(Cat())
But can we assign a Producer<Dog> to a variable of type Producer<Animal>? Intuitively, this should be possible, because a producer of dogs is also a producer of animals. We can always get an animal from it by calling produce(). However, if we try to do this in Kotlin, we get a compiler error:
val animalProducer: Producer<Animal> = dogProducer // Error: Type mismatch
This is because by default, generic types in Kotlin are invariant, meaning that they are not subtypes of each other, even if their type arguments are. This is similar to how Java behaves without wildcards.
To fix this error, we need to make the type parameter Tcovariant, meaning that it preserves the subtype relationship. We can do this by adding the out modifier to the type parameter declaration:
class Producer<out T>(val value: T) { fun produce(): T = value }
The out modifier tells the compiler that T is only used as an output, not as an input. This means that we can only return values of type T from the class, but we cannot accept them as parameters. This ensures that we don’t violate the type safety by putting a wrong value into the class.
With this modifier, we can now assign a Producer<Dog> to a Producer<Animal>, because Producer<Dog> is a subtype of Producer<Animal>:
val animalProducer: Producer<Animal> = dogProducer // OK
This is called covariance, because the subtype relationship varies in the same direction as the type argument. If Dog is a subtype of Animal, then Producer<Dog> is a subtype of Producer<Animal>.
Covariance is useful when we want to read values from a generic class, but not write to it. For example, Kotlin’s standard library defines the interface List<out T> as covariant, because we can only get elements from a list, but not add or remove them. This allows us to assign a List<Dog> to a List<Animal>, which is convenient for polymorphism.
Use-site variance
Another way to achieve variance in Kotlin is by using use-site variance. This means that we can specify the variance of a type parameter at the point where we use it, such as in a function parameter or a variable declaration. This allows us to override the default variance of the class or interface where the type parameter is declared.
For example, let’s define another simple class that represents a consumer of some type T:
class Consumer<T>(var value: T) { fun consume(value: T) { this.value = value } }
This class has a type parameter T that appears as the parameter type of the consume() method. Now, let’s say we have two subtypes of Animal: Dog and Cat. We can create instances of Consumer<Dog> and Consumer<Cat>:
val dogConsumer = Consumer(Dog()) val catConsumer = Consumer(Cat())
But can we assign a Consumer<Animal> to a variable of type Consumer<Dog>? Intuitively, this should be possible, because a consumer of animals can also consume dogs. We can always pass a dog to it by calling consume(). However, if we try to do this in Kotlin, we get a compiler error:
val dogConsumer: Consumer<Dog> = animalConsumer // Error: Type mismatch
This is because by default, generic types in Kotlin are invariant, meaning that they are not subtypes of each other, even if their type arguments are. This is similar to how Java behaves without wildcards.
To fix this error, we need to make the type parameter Tcontravariant, meaning that it reverses the subtype relationship. We can do this by adding the in modifier to the type parameter usage:
val dogConsumer: Consumer<in Dog> = animalConsumer // OK
The in modifier tells the compiler that T is only used as an input, not as an output. This means that we can only accept values of type T as parameters, but we cannot return them from the class. This ensures that we don’t violate the type safety by getting a wrong value from the class.
With this modifier, we can now assign a Consumer<Animal> to a Consumer<Dog>, because Consumer<Animal> is a subtype of Consumer<Dog>:
val dogConsumer: Consumer<in Dog> = animalConsumer // OK
This is called contravariance, because the subtype relationship varies in the opposite direction as the type argument. If Dog is a subtype of Animal, then Consumer<Animal> is a subtype of Consumer<Dog>.
Contravariance is useful when we want to write values to a generic class, but not read from it. For example, Kotlin’s standard library defines the interface MutableList<T> as invariant, because we can both get and set elements in a mutable list. However, if we only want to add elements to a list, we can use the function addAll(elements: Collection<T>), which accepts a collection of any subtype of T. This function uses use-site variance to make the parameter type covariant:
fun <T> MutableList<T>.addAll(elements: Collection<out T>)
This allows us to add a List<Dog> to a MutableList<Animal>, which is convenient for polymorphism.
Comparison with Java
If you are familiar with Java’s generics, you might notice some similarities and differences between Kotlin and Java’s variance mechanisms. Java uses wildcard types (? extends T and ? super T) to achieve covariance and contravariance, respectively. Kotlin uses declaration-site variance (out T and in T) and use-site variance (T and in T) instead.
The main advantage of Kotlin’s approach is that it simplifies the syntax and semantics of generics. Wildcard types can be confusing and verbose, especially when they are nested or combined with other types. Declaration-site variance allows us to specify the variance once at the class level, instead of repeating it at every usage site. Use-site variance allows us to override the default variance when needed, without introducing new types.
Another advantage of Kotlin’s approach is that it avoids some of the limitations and pitfalls of wildcard types. For example, wildcard types cannot be used as return types or in generic type arguments. Declaration-site variance does not have this restriction, as long as the type parameter is used consistently as an output or an input. Use-site variance also allows us to use both covariant and contravariant types in the same context, such as in function parameters or variables.
Conclusion
In this blog, we learned about variance in Kotlin and how it affects the type system and the code we write. We saw how declaration-site variance and use-site variance can help us achieve covariance and contravariance for generic types. We also compared them with Java’s wildcard types and saw how Kotlin simplifies the syntax and semantics of generics.
Variance is an important concept for writing generic and polymorphic code in Kotlin. It allows us to express more precise and flexible types that can adapt to different situations. By understanding how variance works in Kotlin, we can write more idiomatic and effective code with generics.
I hope you enjoyed this blog and learned something new. If you have any questions or feedback, please let me know in the comments below. Thank you for reading! 😊
@Composable fun Greeting(name: String) { Text(text = "Hello, $name!") }
This function defines a simple UI element that displays a text label with a greeting message. You can call this function from another composable function, such as the setContent block that defines the activity’s layout:
This will render the text “Hello, World!” on the screen. You can also pass different parameters to the composable function to customize its behavior. For example:
setContent { Greeting(name = "Android") }
This will render the text “Hello, Android!” on the screen.
How to preview composable functions in Android Studio?
@Preview @Composable fun PreviewGreeting() { Greeting(name = "Compose") }
This function calls the Greeting function with a parameter of “Compose”. You can then see a preview of this function in Android Studio by clicking on the split (design/code) view. You can also refresh the preview at any time by clicking on the refresh button at the top of the preview window.
How to use different types of composable functions?
There are many types of composable functions that you can use to create different UI elements and layouts in Jetpack Compose. Some of the most common ones are:
Text: This function displays a text label on the screen. You can customize its appearance by passing parameters such as color, fontSize, fontWeight, etc.
Image: This function displays an image on the screen. You can load an image from a resource or a URL by using the painterResource or rememberImagePainter functions respectively. You can also adjust its size and shape by using parameters such as modifier, contentScale, contentDescription, etc.
Button: This function displays a button on the screen. You can handle its click event by passing a lambda expression to the onClick parameter. You can also style it by using parameters such as colors, shape, elevation, etc.
Row: This function arranges its children horizontally in a row. You can control how they are aligned and spaced by using parameters such as horizontalArrangement, verticalAlignment, modifier, etc.
Column: This function arranges its children vertically in a column. You can control how they are aligned and spaced by using parameters such as verticalArrangement, horizontalAlignment, modifier, etc.
Box: This function stacks its children on top of each other in a box. You can control how they are positioned and sized by using parameters such as alignment, contentAlignment, modifier, etc.
Here is an example of how to use some of these composable functions to create a simple UI:
This function creates a profile card with an image and some text. You can preview it in Android Studio by adding another function with the @Preview annotation:
GraphQL is a query language for APIs that allows you to specify the data you want from a server in a declarative way. Apollo GraphQL is a popular GraphQL client that generates Kotlin and Java models from GraphQL queries and executes them against a GraphQL server. In this blog post, I will show you how to set up Apollo GraphQL in your Android Kotlin project and how to use it to perform queries, mutations and subscriptions.
Setting up Apollo GraphQL
To use Apollo GraphQL in your Android Kotlin project, you need to add the following dependencies to your build.gradle.kts file:
plugins { id("com.apollographql.apollo3") version "3.8.1" } dependencies { implementation("com.apollographql.apollo3:apollo-runtime:3.8.1") }
You also need to set the package name for the generated models in your apollo block:
apollo { service("service") { packageName.set("com.example") } }
Apollo GraphQL supports three types of files:
.graphqls schema files: describe the types in your backend using the GraphQL syntax.
.json schema files: describe the types in your backend using the JSON syntax.
.graphql executable files: describe your queries and operations in the GraphQL syntax.
By default, Apollo GraphQL requires a schema in your module’s src/main/graphql directory. You can download a schema using introspection with the ./gradlew downloadApolloSchema task.
Writing and executing queries
To write a query, you need to create a .graphql file in your src/main/graphql directory with the following syntax:
query GetPosts($limit: Int) { posts(limit: $limit) { id title author { name } } }
This query will fetch a list of posts with their id, title and author name, and accept a limit argument to limit the number of posts.
Apollo GraphQL will generate a Kotlin class for this query with the same name as the file (GetPostsQuery) and a data class for each type (Post, Author). You can use these classes to execute the query using an ApolloClient instance:
val apolloClient = ApolloClient.Builder() .serverUrl("https://example.com/graphql") .build() val query = GetPostsQuery(limit = 10) apolloClient.query(query).execute().let { response -> if (response.isSuccessfull) { // handle success val posts = response.data?.posts // do something with posts } else { // handle error val error = response.errors?.firstOrNull() // do something with error } }
The execute() method returns an ApolloResponse object that contains either data or errors. You can access the data as query-specific Kotlin types and handle any errors that may occur.
Writing and executing mutations
To write a mutation, you need to create a .graphql file in your src/main/graphql directory with the following syntax:
mutation CreatePost($title: String!, $authorId: ID!) { createPost(input: {title: $title, authorId: $authorId}) { id title author { name } } }
This mutation will create a new post with the given title and author id, and return the created post with its id, title and author name.
Apollo GraphQL will generate a Kotlin class for this mutation with the same name as the file (CreatePostMutation) and a data class for each type (Post, Author). You can use these classes to execute the mutation using an ApolloClient instance:
val apolloClient = ApolloClient.Builder() .serverUrl("https://example.com/graphql") .build() val mutation = CreatePostMutation(title = "Hello world", authorId = "1") apolloClient.mutate(mutation).execute().let { response -> if (response.isSuccessfull) { // handle success val post = response.data?.createPost // do something with post } else { // handle error val error = response.errors?.firstOrNull() // do something with error } }
The execute() method returns an ApolloResponse object that contains either data or errors. You can access the data as mutation-specific Kotlin types and handle any errors that may occur.
Writing and executing subscriptions
To write a subscription, you need to create a .graphql file in your src/main/graphql directory with the following syntax:
subscription OnPostCreated { postCreated { id title author { name } } }
This subscription will listen for new posts created on the server and return the new post with its id, title and author name.
Apollo GraphQL will generate a Kotlin class for this subscription with the same name as the file (OnPostCreatedSubscription) and a data class for each type (Post, Author). You can use these classes to execute the subscription using an ApolloClient instance:
val apolloClient = ApolloClient.Builder() .serverUrl("wss://example.com/graphql") .build() val subscription = OnPostCreatedSubscription() apolloClient.subscribe(subscription).execute().collect { response -> if (response.isSuccessfull) { // handle success val post = response.data?.postCreated // do something with post } else { // handle error val error = response.errors?.firstOrNull() // do something with error } }
The execute() method returns a Flow of ApolloResponse objects that emit data or errors. You can collect the data as subscription-specific Kotlin types and handle any errors that may occur.
Conclusion
In this blog post, I showed you how to use Apollo GraphQL in your Android Kotlin project and how to perform queries, mutations and subscriptions. Apollo GraphQL is a powerful and type-safe GraphQL client that makes it easy to work with GraphQL APIs. You can learn more about Apollo GraphQL from their official documentation12 or their GitHub repository3. I hope you enjoyed this blog post and found it useful. Happy coding! 🚀
Jetpack Compose is a modern toolkit for building native UI on Android. It simplifies and accelerates UI development with declarative and reactive programming. One of the common tasks in UI development is to display images from various sources, such as network, local storage, assets or resources. In this blog post, we will explore how to load images in Jetpack Compose using different libraries and techniques.
Loading images from disk
To load an image from disk, such as a PNG, JPEG, WEBP or vector resource, we can use the Image composable with the painterResource API. The painterResource function takes an image reference (such as a resource ID) and returns a Painter object that can be used to draw the image on the screen. We don’t need to know the type of the asset, just use painterResource in Image or paint modifiers1.
If we need lower-level ImageBitmap specific functionality, we can use ImageBitmap.imageResource function to load up a bitmap. For more information on ImageBitmaps, read the ImageBitmap versus ImageVector section1.
To use any of these libraries in our Android app, we need to add the corresponding dependency to our build.gradle file. Then, we can use their provided composables or extensions to load an image from a URL.
For example, to load an image with Coil:
AsyncImage( model = "https://example.com/image.jpg", contentDescription = "Translated description of what the image contains" )
To load an image with Glide:
GlideImage( model = "https://example.com/image.jpg", contentDescription = "Translated description of what the image contains" )
To load an image with Fresco:
FrescoImage( model = "https://example.com/image.jpg", contentDescription = "Translated description of what the image contains" )
To load an image with Landscapist:
NetworkImage( imageUrl = "https://example.com/image.jpg", contentDescription = "Translated description of what the image contains" )
We can also configure the requests with optional parameters or lambdas to customize the loading behavior and appearance of the images.
Code examples
Here are some code examples of using different libraries to load images from the internet in Jetpack Compose:
Structural design patterns are all about how you compose objects and classes to obtain new functionality. They help you simplify the design by finding a simple way of realizing relationships between entities1. In this blog post, we will cover three common structural design patterns: adapter, decorator and facade. We will also see how to implement them in Kotlin using some of its features such as extension functions, data classes and delegation.
And you have another class that represents a library:class Library { private val books = mutableListOf<Book>() fun addBook(book: Book) { books.add(book) } fun getBooks(): List<Book> { return books } } Copy
Now, suppose you want to use a third-party library that provides a function to print a list of books in a nice format. However, this function expects a list of objects that implement the Printable interface:interface Printable { fun print(): String } Copy
How can you make your Book class compatible with this function? One way is to use the adapter pattern. You can create an adapter class that implements Printable and wraps a Book object:class BookAdapter(private val book: Book) : Printable { override fun print(): String { return "Title: ${book.title}, Author: ${book.author}, Pages: ${book.pages}" } } Copy
Then, you can use this adapter class to convert your list of books into a list of printable objects:val library = Library() library.addBook(Book("The Lord of the Rings", "J.R.R. Tolkien", 1178)) library.addBook(Book("Harry Potter and the Philosopher's Stone", "J.K. Rowling", 223)) library.addBook(Book("The Hitchhiker's Guide to the Galaxy", "Douglas Adams", 180)) val printables = library.getBooks().map { book -> BookAdapter(book) } printBooks(printables) // This is the third-party function that expects a list of Printable objects Copy
Alternatively, you can use an extension function to achieve the same result without creating an adapter class:fun Book.toPrintable(): Printable { return object : Printable { override fun print(): String { return "Title: ${this@toPrintable.title}, Author: ${this@toPrintable.author}, Pages: ${this@toPrintable.pages}" } } } val printables = library.getBooks().map { book -> book.toPrintable() } printBooks(printables) Copy
The advantage of using an extension function is that it reduces the amount of code and classes needed. However, it may not be suitable for complex scenarios where you need more control over the adaptation logic.
And you have a concrete class that implements this interface:class Espresso : Coffee { override fun cost(): Double { return 1.5 } override fun description(): String { return "Espresso" } } Copy
Now, suppose you want to add some extra ingredients to your coffee, such as milk, whipped cream or caramel. One way is to use the decorator pattern. You can create an abstract class that implements Coffee and wraps another Coffee object:abstract class CoffeeDecorator(private val coffee: Coffee) : Coffee { override fun cost(): Double { return coffee.cost() } override fun description(): String { return coffee.description() } } Copy
Then, you can create concrete subclasses that extend this abstract class and add their own logic:class Milk(private val coffee: Coffee) : CoffeeDecorator(coffee) { override fun cost(): Double { return super.cost() + 0.5 } override fun description(): String { return "${super.description()}, Milk" } } class WhippedCream(private val coffee: Coffee) : CoffeeDecorator(coffee) { override fun cost(): Double { return super.cost() + 0.7 } override fun description(): String { return "${super.description()}, Whipped Cream" } } class Caramel(private val coffee: Coffee) : CoffeeDecorator(coffee) { override fun cost(): Double { return super.cost() + 0.8 } override fun description(): String { return "${super.description()}, Caramel" } } Copy
Then, you can use these decorator classes to create different combinations of coffee:val espresso = Espresso() println("${espresso.description()} costs ${espresso.cost()}") // Espresso costs 1.5 val espressoWithMilk = Milk(espresso) println("${espressoWithMilk.description()} costs ${espressoWithMilk.cost()}") // Espresso, Milk costs 2.0 val espressoWithMilkAndWhippedCream = WhippedCream(espressoWithMilk) println("${espressoWithMilkAndWhippedCream.description()} costs ${espressoWithMilkAndWhippedCream.cost()}") // Espresso, Milk, Whipped Cream costs 2.7 val espressoWithMilkAndWhippedCreamAndCaramel = Caramel(espressoWithMilkAndWhippedCream) println("${espressoWithMilkAndWhippedCreamAndCaramel.description()} costs ${espressoWithMilkAndWhippedCreamAndCaramel.cost()}") // Espresso, Milk, Whipped Cream, Caramel costs 3.5 Copy
Alternatively, you can use delegation instead of inheritance to implement the decorator pattern in Kotlin. You can create an interface that represents a decorator:interface Decorator<T> : T { val delegate: T } Copy
Then, you can create concrete classes that implement this interface and delegate all the requests to the wrapped object while adding their own logic:class Milk(override val delegate: Coffee) : Decorator<Coffee>, Coffee by delegate { override fun cost(): Double { return delegate.cost() + 0.5 } override fun description(): String { return "${delegate.description()}, Milk" } } class WhippedCream(override val delegate: Coffee) : Decorator<Coffee>, Coffee by delegate { override fun cost(): Double { return delegate.cost() + 0.7 } override fun description(): String { return "${delegate.description()}, Whipped Cream" } } class Caramel(override val delegate: Coffee) : Decorator<Coffee>, Coffee by delegate { override fun cost(): Double { return delegate.cost() + 0.8 } override fun description(): String { return "${delegate.description()}, Caramel" } } Copy
Then, you can use these decorator classes to create different combinations of coffee as before:val espresso = Espresso() println("${espresso.description()} costs ${espresso.cost()}") // Espresso costs 1.5 val espressoWithMilk = Milk(espresso) println("${espressoWithMilk.description()} costs ${espressoWithMilk.cost()}") // Espresso, Milk costs 2.0 val espressoWithMilkAndWhippedCream = WhippedCream(espressoWithMilk) println("${espressoWithMilkAndWhippedCream.description()} costs ${espressoWithMilkAndWhippedCream.cost()}") // Espresso, Milk, Whipped Cream costs 2.7 val espressoWithMilkAndWhippedCreamAndCaramel = Caramel(espressoWithMilkAndWhippedCream) println("${espressoWithMilkAndWhippedCreamAndCaramel.description()} costs ${espressoWithMilkAndWhippedCreamAndCaramel.cost()}") // Espresso, Milk, Whipped Cream, Caramel costs 3.5 Copy
The advantage of using delegation is that it avoids creating unnecessary subclasses and makes the code more concise and readable.
Facade Pattern
The facade pattern simplifies the interaction with a complex system or library by providing a unified and easy-to-use interface. It hides the details and implementation of the system from the clients and exposes only the essential functionality. For example, suppose you have a complex library that offers various functions for image processing:class ImageProcessingLibrary { fun loadBitmap(path: String): Bitmap { ... } fun resizeBitmap(bitmap: Bitmap, width: Int, height: Int): Bitmap { ... } fun cropBitmap(bitmap: Bitmap, x: Int, y: Int, width: Int, height: Int): Bitmap { ... } fun applyFilter(bitmap: Bitmap, filter: Filter): Bitmap { ... } fun saveBitmap(bitmap: Bitmap, path: String) { ... } // ... more functions } Copy
Using this library directly may be cumbersome and error-prone for the clients. They need to know how to use each function correctly and in what order. For example, if they want to load an image from a file, resize it, apply a filter and save it back to another file, they need to write something like this:val library = ImageProcessingLibrary() val bitmap = library.loadBitmap("input.jpg") val resizedBitmap = library.resizeBitmap(bitmap, 300, 300) val filteredBitmap = library.applyFilter(resizedBitmap, Filter.GRAYSCALE) library.saveBitmap(filteredBitmap, "output.jpg") Copy
To make this task easier and more convenient, you can use the facade pattern. You can create a class that acts as a facade for the library and provides a simple interface for common operations:class ImageProcessor(private val library: ImageProcessingLibrary) { fun processImage(inputPath: String, outputPath: String, width: Int, height: Int, filter: Filter) { val bitmap = library.loadBitmap(inputPath) val resizedBitmap = library.resizeBitmap(bitmap, width, height) val filteredBitmap = library.applyFilter(resizedBitmap, filter) library.saveBitmap(filteredBitmap, outputPath) } // ... more functions for other operations } Copy
Then, the clients can use this facade class to perform the same operation with less code and complexity:val processor = ImageProcessor(ImageProcessingLibrary()) processor.processImage("input.jpg", "output.jpg", 300, 300, Filter.GRAYSCALE) Copy
The advantage of using the facade pattern is that it reduces the coupling between the clients and the system or library. It also improves the readability and maintainability of the code by encapsulating the logic and details of the system or library in one place.
Conclusion
In this blog post, we have learned about three common structural design patterns: adapter, decorator and facade. We have seen how they can help us simplify the design and implementation of our Android applications by composing objects and classes in different ways. We have also seen how to implement them in Kotlin using some of its features such as extension functions, data classes and delegation. We hope you have enjoyed this post and found it useful. If you have any questions or feedback, please feel free to leave a comment below. Happy coding!
