activity/activity-compose/src/main/java/androidx/activity/compose/ComponentActivity.kt

/*
 * Copyright 2021 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package androidx.activity.compose

import android.view.ViewGroup
import androidx.activity.ComponentActivity
import androidx.compose.runtime.Composable
import androidx.compose.runtime.CompositionContext
import androidx.compose.ui.platform.ComposeView
import androidx.lifecycle.ViewTreeLifecycleOwner
import androidx.lifecycle.ViewTreeViewModelStoreOwner
import androidx.savedstate.ViewTreeSavedStateRegistryOwner

/**
 * Composes the given composable into the given activity. The [content] will become the root view
 * of the given activity.
 *
 * This is roughly equivalent to calling [ComponentActivity.setContentView] with a [ComposeView]
 * i.e.:
 *
 * ```
 * setContentView(
 *   ComposeView(this).apply {
 *     setContent {
 *       MyComposableContent()
 *     }
 *   }
 * )
 * ```
 *
 * @param parent The parent composition reference to coordinate scheduling of composition updates
 * @param content A `@Composable` function declaring the UI contents
 */
public fun ComponentActivity.setContent(
    parent: CompositionContext? = null,
    content: @Composable () -> Unit
) {
    val existingComposeView = window.decorView
        .findViewById<ViewGroup>(android.R.id.content)
        .getChildAt(0) as? ComposeView

    if (existingComposeView != null) with(existingComposeView) {
        setParentCompositionContext(parent)
        setContent(content)
    } else ComposeView(this).apply {
        // Set content and parent **before** setContentView
        // to have ComposeView create the composition on attach
        setParentCompositionContext(parent)
        setContent(content)
        // Set the view tree owners before setting the content view so that the inflation process
        // and attach listeners will see them already present
        setOwners()
        setContentView(this, DefaultActivityContentLayoutParams)
    }
}

private val DefaultActivityContentLayoutParams = ViewGroup.LayoutParams(
    ViewGroup.LayoutParams.WRAP_CONTENT,
    ViewGroup.LayoutParams.WRAP_CONTENT
)

/**
 * These owners are not set before AppCompat 1.3+ due to a bug, so we need to set them manually in
 * case developers are using an older version of AppCompat.
 */
private fun ComponentActivity.setOwners() {
    val decorView = window.decorView
    if (ViewTreeLifecycleOwner.get(decorView) == null) {
        ViewTreeLifecycleOwner.set(decorView, this)
    }
    if (ViewTreeViewModelStoreOwner.get(decorView) == null) {
        ViewTreeViewModelStoreOwner.set(decorView, this)
    }
    if (ViewTreeSavedStateRegistryOwner.get(decorView) == null) {
        ViewTreeSavedStateRegistryOwner.set(decorView, this)
    }
}