如何在 WindowManager.addView 中使用 Jetpack Compose

一、引出问题

Android 开发中，很常见的一个场景，通过 WindowManager.addView() 添加一个 View 到屏幕上。Android 最新的视图框架 Jetpack Compose，如何应用进来。这个被添加的 View 如何使用 Compose 编写视图呢？

二、探究问题

有的朋友肯定会马上想到使用 ComposeView 作为桥梁。没错，WindowManager.addView 方法，就接收一个 View 类型的参数。那肯定是要借助 ComposeView 了。但是，经过试验，直接使用 ComposeView 是行不通的。
看代码：

val params = WindowManager.LayoutParams(
    WindowManager.LayoutParams.WRAP_CONTENT,
    WindowManager.LayoutParams.WRAP_CONTENT,
    WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY,
    WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
    PixelFormat.TRANSLUCENT
)

val composeView: ComposeView = ComposeView(this).apply {
    setContent {
        Text(text = "I'm be added")
    }
}

windowManager.addView(composeView, params)

上面代码，编译没有问题，运行时会报错：

FATAL EXCEPTION: main
Process: xxxxxxxx
java.lang.IllegalStateException: ViewTreeLifecycleOwner not found from androidx.compose.ui.platform.ComposeView{8285855 V.E...... ......I. 0,0-0,0}
    at androidx.compose.ui.platform.WindowRecomposer_androidKt.createLifecycleAwareWindowRecomposer(WindowRecomposer.android.kt:352)
    at androidx.compose.ui.platform.WindowRecomposer_androidKt.createLifecycleAwareWindowRecomposer$default(WindowRecomposer.android.kt:325)
    at androidx.compose.ui.platform.WindowRecomposerFactory$Companion$LifecycleAware$1.createRecomposer(WindowRecomposer.android.kt:168)
    at androidx.compose.ui.platform.WindowRecomposerPolicy.createAndInstallWindowRecomposer$ui_release(WindowRecomposer.android.kt:224)
    at androidx.compose.ui.platform.WindowRecomposer_androidKt.getWindowRecomposer(WindowRecomposer.android.kt:300)
    at androidx.compose.ui.platform.AbstractComposeView.resolveParentCompositionContext(ComposeView.android.kt:244)
    at androidx.compose.ui.platform.AbstractComposeView.ensureCompositionCreated(ComposeView.android.kt:251)
    at androidx.compose.ui.platform.AbstractComposeView.onAttachedToWindow(ComposeView.android.kt:283)
    at android.view.View.dispatchAttachedToWindow(View.java:22065)
    at android.view.ViewGroup.dispatchAttachedToWindow(ViewGroup.java:3553)
    ...

看这个错误信息：
应该是从 ComposeView 中没有找到 ViewTreeLifecycleOwner，其实很好理解。 View 的生命周期依赖于 ViewTreeLifecycleOwner， ComposeView 依赖于一个 ViewCompositonStrategy。核心问题是，ComposeView 需要一个 Lifecycle。

三、解决问题

有了思路自然就尝试解决问题。
首先定义一个 LifecycleOwner ，

import android.view.View
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.LifecycleRegistry
import androidx.lifecycle.ViewModelStore
import androidx.lifecycle.ViewModelStoreOwner
import androidx.lifecycle.setViewTreeLifecycleOwner
import androidx.lifecycle.setViewTreeViewModelStoreOwner
import androidx.savedstate.SavedStateRegistry
import androidx.savedstate.SavedStateRegistryController
import androidx.savedstate.SavedStateRegistryOwner
import androidx.savedstate.setViewTreeSavedStateRegistryOwner

class MyComposeViewLifecycleOwner:
    LifecycleOwner, ViewModelStoreOwner, SavedStateRegistryOwner {

    private val lifecycleRegistry: LifecycleRegistry = LifecycleRegistry(this)
    private val savedStateRegistryController = SavedStateRegistryController.create(this)
    private val store = ViewModelStore()

    override val lifecycle: Lifecycle
        get() = lifecycleRegistry
    override val savedStateRegistry: SavedStateRegistry
        get() = savedStateRegistryController.savedStateRegistry
    override val viewModelStore: ViewModelStore
        get() = store


    fun onCreate() {
        savedStateRegistryController.performRestore(null)
        lifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_CREATE)
    }

    fun onStart() {
        lifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_START)
    }

    fun onResume() {
        lifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_RESUME)
    }

    fun onPause() {
        lifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    }

    fun onStop() {
        lifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_STOP)
    }

    fun onDestroy() {
        lifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_DESTROY)
        store.clear()
    }

    /**
     * Compose uses the Window's decor view to locate the
     * Lifecycle/ViewModel/SavedStateRegistry owners.
     * Therefore, we need to set this class as the "owner" for the decor view.
     */
    fun attachToDecorView(decorView: View?) {
        decorView?.let {
            it.setViewTreeViewModelStoreOwner(this)
            it.setViewTreeLifecycleOwner(this)
            it.setViewTreeSavedStateRegistryOwner(this)
        } ?: return
    }
}

再看看使用：

private var lifecycleOwner: MyComposeViewLifecycleOwner? = null

val params = WindowManager.LayoutParams(
    WindowManager.LayoutParams.WRAP_CONTENT,
    WindowManager.LayoutParams.WRAP_CONTENT,
    WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY,
    WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
    PixelFormat.TRANSLUCENT
)

val composeView: ComposeView = ComposeView(this).apply {
    setContent {
        Text(text = "I'm be added")
    }
}


// 注意，在 调用 addView 之前：
lifecycleOwner = MyComposeViewLifecycleOwner().also {
                        it.onCreate() // 注意
                        it.attachToDecorView(composeView)
                    }
windowManager.addView(composeView, params)




windowManager.removeViewImmediate(composeView)
lifecycleOwner?.onDestroy()
lifecycleOwner = null

OK，再次运行。成功~