AndroidView

Composable Function

Android

@Composable
fun <T : View> AndroidView(
    factory: (Context) -> T,
    modifier: Modifier = Modifier,
    update: (T) -> Unit = NoOpUpdate,
)

Composes an Android View obtained from factory. The factory block will be called exactly once to obtain the View being composed, and it is also guaranteed to be invoked on the UI thread. Therefore, in addition to creating the View, the factory block can also be used to perform one-off initializations and View constant properties' setting. The update block can run multiple times (on the UI thread as well) due to recomposition, and it is the right place to set the new properties. Note that the block will also run once right after the factory block completes.

AndroidView is commonly needed for using Views that are infeasible to be reimplemented in Compose and there is no corresponding Compose API. Common examples for the moment are WebView, SurfaceView, AdView, etc.

This overload of AndroidView does not automatically pool or reuse Views. If placed inside of a reusable container (including inside a LazyRow or LazyColumn), the View instances will always be discarded and recreated if the composition hierarchy containing the AndroidView changes, even if its group structure did not change and the View could have conceivably been reused.

To opt-in for View reuse, call the overload of AndroidView that accepts an onReset callback, and provide a non-null implementation for this callback. Since it is expensive to discard and recreate View instances, reusing Views can lead to noticeable performance improvements — especially when building a scrolling list of AndroidViews. It is highly recommended to opt-in to View reuse when possible.

AndroidView will not clip its content to the layout bounds. Use View.setClipToOutline on the child View to clip the contents, if desired. Developers will likely want to do this with all subclasses of SurfaceView to keep its contents contained.

AndroidView has nested scroll interop capabilities if the containing view has nested scroll enabled. This means this Composable can dispatch scroll deltas if it is placed inside a container that participates in nested scroll. For more information on how to enable nested scroll interop:

Parameters


factory	The block creating the `View` to be composed.
modifier	The modifier to be applied to the layout.
update	A callback to be invoked after the layout is inflated and upon recomposition to update the information and state of the view.

Android

@Composable
fun <T : View> AndroidView(
    factory: (Context) -> T,
    modifier: Modifier = Modifier,
    onReset: ((T) -> Unit)? = null,
    onRelease: (T) -> Unit = NoOpUpdate,
    update: (T) -> Unit = NoOpUpdate,
)

By default, AndroidView does not automatically pool or reuse Views. If placed inside of a reusable container (including inside a LazyRow or LazyColumn), the View instances will always be discarded and recreated if the composition hierarchy containing the AndroidView changes, even if its group structure did not change and the View could have conceivably been reused.

Views are eligible for reuse if AndroidView is given a non-null onReset callback. Since it is expensive to discard and recreate View instances, reusing Views can lead to noticeable performance improvements — especially when building a scrolling list of AndroidViews. It is highly recommended to specify an onReset implementation and opt-in to View reuse when possible.

When onReset is specified, View instances may be reused when hosted inside of a container that supports reusable elements. Reuse occurs when compatible instances of AndroidView are inserted and removed during recomposition. Two instances of AndroidView are considered compatible if they are invoked with the same composable group structure. The most common scenario where this happens is in lazy layout APIs like LazyRow and LazyColumn, which can reuse layout nodes (and Views, in this case) between items when scrolling.

onReset is invoked on the UI thread when the View will be reused, signaling that the View should be prepared to appear in a new context in the composition hierarchy. This callback is invoked before update and may be used to reset any transient View state like animations or user input.

Note that onReset may not be immediately followed by a call to update. Compose may temporarily detach the View from the composition hierarchy if it is deactivated but not released from composition. This can happen if the View appears in a ReusableContentHost that is not currently active or inside of a movable content block that is being moved. If this happens, the View will be removed from its parent, but retained by Compose so that it may be reused if its content host becomes active again. If the View never becomes active again and is instead discarded entirely, the onReset callback will be invoked directly from this deactivated state when Compose releases the View.

If you need to observe whether the View is currently used in the composition hierarchy, you may observe whether it is attached via View.addOnAttachStateChangeListener. The View may also observe the lifecycle of its host via findViewTreeLifecycleOwner. The lifecycle returned by this function will match the LocalLifecycleOwner. Note that the lifecycle is not set and cannot be used until the View is attached.

When the View is removed from the composition permanently, onRelease will be invoked (also on the UI thread). Once this callback returns, Compose will never attempt to reuse the previous View instance regardless of whether an onReset implementation was provided. If the View is needed again in the future, a new instance will be created, with a fresh lifecycle that begins by calling the factory.

Parameters


factory	The block creating the `View` to be composed.
modifier	The modifier to be applied to the layout.
onReset	A callback invoked as a signal that the view is about to be attached to the composition hierarchy in a different context than its original creation. This callback is invoked before `update` and should prepare the view for general reuse. If `null` or not specified, the `AndroidView` instance will not support reuse, and the View instance will always be discarded whenever the AndroidView is moved or removed from the composition hierarchy.
onRelease	A callback invoked as a signal that this view instance has exited the composition hierarchy entirely and will not be reused again. Any additional resources used by the View should be freed at this time.
update	A callback to be invoked after the layout is inflated and upon recomposition to update the information and state of the view.

Code Examples

ViewInComposeNestedScrollInteropSample

@Composable
fun ViewInComposeNestedScrollInteropSample() {
    Box(
        Modifier.fillMaxSize()
            .scrollable(
                rememberScrollableState {
                    // view world deltas should be reflected in compose world
                    // components that participate in nested scrolling
                    it
                },
                Orientation.Vertical,
            )
    ) {
        AndroidView({ context ->
            LayoutInflater.from(context).inflate(android.R.layout.activity_list_item, null).apply {
                // Nested Scroll Interop will be Enabled when
                // nested scroll is enabled for the root view
                ViewCompat.setNestedScrollingEnabled(this, true)
            }
        })
    }
}

AndroidViewSample

@Suppress("SetTextI18n")
@Composable
fun AndroidViewSample() {
    // Compose a TextView.
    AndroidView({ context -> TextView(context).apply { text = "This is a TextView" } })
    // Compose a View and update its size based on state. Note the modifiers.
    var size by remember { mutableStateOf(20) }
    AndroidView(::View, Modifier.clickable { size += 20 }.background(Color.Blue)) { view ->
        view.layoutParams = ViewGroup.LayoutParams(size, size)
    }
}

ReusableAndroidViewInLazyColumnSample

@Composable
fun ReusableAndroidViewInLazyColumnSample() {
    val urls =
        listOf(
            "https://developer.android.com/jetpack/compose",
            "https://google.github.io/accompanist/",
            "https://android-developers.googleblog.com/",
            "https://io.google/",
            // ...
        )
    LazyVerticalGrid(columns = GridCells.Adaptive(512.dp)) {
        items(urls) { url ->
            AndroidView(
                factory = { context ->
                    WebView(context).apply {
                        settings.javaScriptEnabled = true
                        webViewClient =
                            object : WebViewClient() {
                                // Optional overrides for WebViewClient
                            }
                    }
                },
                modifier = Modifier.fillMaxWidth().aspectRatio(1f),
                update = { webView -> webView.loadUrl(url) },
                onReset = { webView ->
                    webView.stopLoading()
                    webView.loadUrl("about:blank")
                    webView.clearHistory()
                },
            )
        }
    }
}

AndroidViewWithReleaseSample

@Suppress("UNUSED_ANONYMOUS_PARAMETER")
@Composable
fun AndroidViewWithReleaseSample() {
    // Compose a View that needs to be cleaned up when removed from the UI
    class LifecycleAwareView(context: Context) : View(context) {
        var lifecycle: Lifecycle? = null
            set(value) {
                field?.removeObserver(observer)
                value?.addObserver(observer)
                field = value
            }
        private val observer = LifecycleEventObserver { source, event ->
            // React to the event
        }
    }
    val lifecycle = LocalLifecycleOwner.current.lifecycle
    AndroidView(
        factory = { context -> LifecycleAwareView(context) },
        update = { view -> view.lifecycle = lifecycle },
        onRelease = { view ->
            // Need to release the lifecycle to prevent a memory leak
            view.lifecycle = null
        },
    )
}