Mar 8
Coroutine in Compose
In Compose for Kotlin, a coroutine is a lightweight thread of execution that can be used to perform asynchronous and non-blocking operations, such as making a network request or accessing a database.
👉🏻 Coroutines allow you to write asynchronous code in a more concise and readable way than traditional Java threads, using Kotlin’s suspend functions and the suspendCoroutine operator.
In this updated example, we create a coroutine scope inside the onClick lambda expression of the Button component. We launch a coroutine using this scope to increment the count variable. Since we are not performing a side effect that affects the UI, such as modifying a mutable state variable, we can launch the coroutine outside of a @Composable function.
In this example, we use a coroutine to simulate loading data and update the UI when the data is loaded. When the user clicks the “Load Data” button, we set the isLoading variable to true and launch a coroutine using a new CoroutineScope. Inside the coroutine, we simulate loading data by delaying for 2 seconds using delay(2000). After the delay, we update the data variable on the main thread using withContext(Dispatchers.Main) and set the isLoading variable to false.
By launching the coroutine outside of the @Composable function and updating the UI inside the coroutine using withContext(Dispatchers.Main), we can perform a long-running task without blocking the UI and update the UI when the task is complete.
You can call a suspend function from a Composable function in Kotlin using a coroutine builder such as launch, async, or withContext.
In this example, we use LaunchedEffect to call mySuspendFunction( ) and update the state with the result. We use withContext to call the suspend function on a background thread to avoid blocking the UI thread. When the coroutine completes, we update the state with the returned result.
Note that it’s important to call suspend functions on a background thread to avoid blocking the UI thread and causing the app to become unresponsive. You can use coroutines to launch the suspend function on a background thread and update the UI when the result is ready.
To launch a coroutine from a Composable function in Compose, you can use the LaunchedEffect composable. LaunchedEffect is a Composable function that takes a key and a lambda as parameters. The lambda is executed asynchronously in a coroutine scope when the key changes. Here's an example of how to use LaunchedEffect to launch a coroutine from a Composable function:
In this example, we define a Composable function MyComposable. We use LaunchedEffect to launch a coroutine with the key Unit. The lambda passed to LaunchedEffect is the code that will be executed asynchronously in the coroutine scope.
In this example, we use the LaunchedEffect composable to launch a coroutine when the composable is first rendered. We then use the withContext function to perform a long-running task on a background thread, and update the UI with the result.
Within the lambda, you can use suspend functions like withContext and delay to perform asynchronous operations. Here's an example of how you might use LaunchedEffect to fetch data from a remote API:
In this example, we use LaunchedEffect to launch a coroutine that fetches data from a remote API using the withContext function to perform the fetch operation on the Dispatcher.IO dispatcher. Once the data has been fetched, we update the data state variable with the new data.
Note that LaunchedEffect will automatically cancel and restart the coroutine whenever the key changes. In this example, we use Unit as the key because we only want to launch the coroutine once when the Composable function is first rendered. If you need to launch the coroutine based on a different condition, you can pass that condition as the key instead.
