你遇到的核心问题是误用了setContent方法——它的作用是替换Activity的整个根内容视图，而不是在现有布局上层添加叠加层，所以点击按钮后原来的XML布局就被覆盖了。下面给出两种场景的解决方案：

方案一：在当前Activity布局上层显示Popup（无需额外权限） #

这种方案适合只需要在当前App内显示叠加层的场景，我们可以在原有XML布局中嵌入一个全屏的ComposeView，初始隐藏，点击按钮时再显示它并渲染Popup。

步骤1：修改XML布局 #

添加一个全屏的ComposeView，放在所有控件的最后（确保层级在上层）：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="21dp"
        android:text="Button"
        android:onClick="showComposeView"
        app:layout_constraintStart_toStartOf="@+id/textView"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

    <!-- 全屏ComposeView，初始隐藏，用来承载Popup -->
    <androidx.compose.ui.platform.ComposeView
        android:id="@+id/overlayComposeView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="gone"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

步骤2：修改MainActivity代码 #

初始化ComposeView，点击按钮时显示它并渲染Popup，同时添加点击外部关闭的逻辑：

class MainActivity : AppCompatActivity() {
    private lateinit var overlayComposeView: ComposeView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        overlayComposeView = findViewById(R.id.overlayComposeView)
    }

    fun showComposeView(view: android.view.View) {
        overlayComposeView.visibility = View.VISIBLE
        overlayComposeView.setContent {
            // 全屏半透明背景，点击外部关闭Popup
            Box(
                modifier = Modifier
                    .fillMaxSize()
                    .background(Color.Black.copy(alpha = 0.3f))
                    .clickable { overlayComposeView.visibility = View.GONE }
            ) {
                MyView().pop {
                    // Popup关闭时同步隐藏ComposeView
                    overlayComposeView.visibility = View.GONE
                }
            }
        }
    }
}

步骤3：优化MyView的Popup实现 #

添加关闭回调，同时防止点击Popup内容触发外部关闭：

class MyView {
    @Composable
    fun pop(onDismiss: () -> Unit) {
        val popupWidth = 200.dp
        val popupHeight = 50.dp
        val cornerSize = 16.dp
        
        Popup(
            alignment = Alignment.Center,
            onDismissRequest = onDismiss
        ) {
            Box(
                Modifier
                    .size(popupWidth, popupHeight)
                    .background(Color.White, RoundedCornerShape(cornerSize))
                    .clickable(enabled = false) {} // 拦截点击，避免触发外部背景的关闭逻辑
            ) {
                // 添加Popup内部内容，比如文本
                Text(
                    text = "我的悬浮弹窗",
                    modifier = Modifier.align(Alignment.Center),
                    color = Color.Black
                )
            }
        }
    }
}

方案二：全局悬浮窗Overlay（可显示在其他App上层） #

如果需要弹窗能够显示在所有App的上层，就需要申请SYSTEM_ALERT_WINDOW权限，并通过WindowManager添加ComposeView。

步骤1：添加权限到Manifest #

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

步骤2：修改MainActivity实现权限请求和悬浮窗逻辑 #

class MainActivity : AppCompatActivity() {
    private val REQUEST_OVERLAY_PERMISSION = 1001
    private var overlayView: View? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    fun showComposeView(view: android.view.View) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            // Android 6.0以上需要动态申请权限
            if (!Settings.canDrawOverlays(this)) {
                val intent = Intent(
                    Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
                    Uri.parse("package:$packageName")
                )
                startActivityForResult(intent, REQUEST_OVERLAY_PERMISSION)
            } else {
                showGlobalOverlay()
            }
        } else {
            // 6.0以下直接显示
            showGlobalOverlay()
        }
    }

    private fun showGlobalOverlay() {
        if (overlayView != null) return

        val composeView = ComposeView(this).apply {
            setContent {
                MyView().pop {
                    removeGlobalOverlay()
                }
            }
        }

        // 配置悬浮窗参数
        val layoutParams = WindowManager.LayoutParams(
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.WRAP_CONTENT,
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY
            } else {
                WindowManager.LayoutParams.TYPE_PHONE
            },
            WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE or WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN,
            PixelFormat.TRANSLUCENT
        )
        layoutParams.gravity = Gravity.CENTER

        val windowManager = getSystemService(WINDOW_SERVICE) as WindowManager
        windowManager.addView(composeView, layoutParams)
        overlayView = composeView
    }

    private fun removeGlobalOverlay() {
        overlayView?.let {
            (getSystemService(WINDOW_SERVICE) as WindowManager).removeView(it)
            overlayView = null
        }
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if (requestCode == REQUEST_OVERLAY_PERMISSION) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && Settings.canDrawOverlays(this)) {
                showGlobalOverlay()
            } else {
                Toast.makeText(this, "需要授予悬浮窗权限才能显示弹窗", Toast.LENGTH_SHORT).show()
            }
        }
    }
}

这样就能实现全局悬浮窗效果，弹窗可以显示在任何App的上层。

内容的提问来源于stack exchange，提问作者Prabhu M