Android实现悬浮窗的简单方法实例

1. 前言

现在很多应用都有小悬浮窗的功能，比如看直播的时候，通过Home键返回桌面，直播的小窗口仍可以在屏幕上显示。下面将介绍下悬浮窗的的一种简单实现方式。

2.原理

Window我们应该很熟悉，它是一个接口类，具体的实现类为PhoneWindow，它可以对View进行管理。WindowManager是一个接口类，继承自ViewManager，从名称就知道它是用来管理Window的，它的实现类是WindowManagerImpl。如果我们想要对Window（View）进行添加、更新和删除操作就可以使用WindowManager，WindowManager会将具体的工作交由WindowManagerService处理。这里我们只需要知道WindowManager能用来管理Window就好。

WindowManager是一个接口类，继承自ViewManager，ViewManager中定义了3个方法，分布用来添加、更新和删除View，如下所示：

public interface ViewManager {
    public void addView(View view, ViewGroup.LayoutParams params);
    public void updateViewLayout(View view, ViewGroup.LayoutParams params);
    public void removeView(View view);
}

WindowManager也继承了这些方法，而这些方法传入的参数都是View类型，说明了Window是以View的形式存在的。

3.具体实现

3.1浮窗布局

悬浮窗的简易布局如下的可参考下面的layout_floating_window.xml文件。顶层深色部分的FrameLayout布局是用来实现悬浮窗的拖拽功能的，点击右上角ImageView可以实现关闭悬浮窗，剩下区域显示内容，这里只是简单地显示文本内容，不做复杂的东西，故只设置TextView。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <FrameLayout
        android:id="@+id/layout_drag"
        android:layout_width="match_parent"
        android:layout_height="15dp"
        android:background="#dddddd">
        <androidx.appcompat.widget.AppCompatImageView
            android:id="@+id/iv_close"
            android:layout_width="15dp"
            android:layout_height="15dp"
            android:layout_gravity="end"
            android:src="@drawable/img_delete"/>
    </FrameLayout>

    <androidx.appcompat.widget.AppCompatTextView
        android:id="@+id/tv_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center_horizontal"
        android:background="#eeeeee"
        android:scrollbars="vertical"/>
</LinearLayout>

3.2 悬浮窗的实现

1. 使用服务Service

Service 是一种可在后台执行长时间运行操作而不提供界面的应用组件，可由其他应用组件启动，而且即使用户切换到其他应用，仍将在后台继续运行。要保证应用在后台时，悬浮窗仍然可以正常显示，所以这里可以使用Service。

2. 获取WindowManager并设置LayoutParams

private lateinit var windowManager: WindowManager
private lateinit var layoutParams: WindowManager.LayoutParams
override fun onCreate() {
    // 获取WindowManager
    windowManager = getSystemService(WINDOW_SERVICE) as WindowManager
    layoutParams = WindowManager.LayoutParams().apply {
        // 实现在其他应用和窗口上方显示浮窗
        type = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY
        } else {
            WindowManager.LayoutParams.TYPE_PHONE
        }
        format = PixelFormat.RGBA_8888
        // 设置浮窗的大小和位置
        gravity = Gravity.START or Gravity.TOP
        flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL or WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
        width = 600
        height = 600
        x = 300
        y = 300
    }
}

3. 创建View并添加到WindowManager

private lateinit var floatingView: View
override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
    if (Settings.canDrawOverlays(this)) {
        floatingView = LayoutInflater.from(this).inflate(R.layout.layout_floating_window.xml, null)
        windowManager.addView(floatingView, layoutParams)
    }  
    return super.onStartCommand(intent, flags, startId)
}

4. 实现悬浮窗的拖拽和关闭功能

// 浮窗的坐标
private var x = 0
private var y = 0

override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {   
    if (Settings.canDrawOverlays(this)) {
    floatingView = LayoutInflater.from(this).inflate(R.layout.layout_floating_window.xml, null)
    windowManager.addView(floatingView, layoutParams)

    // 点击浮窗的右上角关闭按钮可以关闭浮窗
    floatingView.findViewById<AppCompatImageView>(R.id.iv_close).setOnClickListener {
     windowManager.removeView(floatingView)
    }
    // 实现浮窗的拖动功能, 通过改变layoutParams来实现
    floatingView.findViewById<AppCompatImageView>(R.id.layout_drag).setOnTouchListener { v, event ->
     when (event.action) {
            MotionEvent.ACTION_DOWN -> {
                x = event.rawX.toInt()
                y = event.rawY.toInt()
            }
            MotionEvent.ACTION_MOVE -> {
                val currentX = event.rawX.toInt()
                val currentY = event.rawY.toInt()
                val offsetX = currentX - x
                val offsetY = currentY - y
                x = currentX
                y = currentY
                layoutParams.x = layoutParams.x + offsetX
                layoutParams.y = layoutParams.y + offsetY
                // 更新floatingView
                windowManager.updateViewLayout(floatingView, layoutParams)
            }
        }
        true
    }
    return super.onStartCommand(intent, flags, startId)
}

5. 利用广播进行通信

private var receiver: MyReceiver? = null
override fun onCreate() {
    // 注册广播
    receiver = MyReceiver()
    val filter = IntentFilter()
    filter.addAction("android.intent.action.MyReceiver")
    registerReceiver(receiver, filter)
}

inner class MyReceiver : BroadcastReceiver() {
    override fun onReceive(context: Context, intent: Intent) {
        val content = intent.getStringExtra("content") ?: ""

        // 通过Handler更新UI
        val message = Message.obtain()
        message.what = 0
        message.obj = content
        handler.sendMessage(message)
    }
}

val handler = Handler(this.mainLooper) { msg ->
    tvContent.text = msg.obj as String
    false
}

可以在Activity中通过广播给Service发送信息

fun sendMessage(view: View?) {
    Intent("android.intent.action.MyReceiver").apply {
        putExtra("content", "Hello, World!")
        sendBroadcast(this)
    }
}

6. 设置权限

悬浮窗的显示需要权限，在AndroidManefest.xml中添加：

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

此外，还要通过Settings.ACTION_MANAGE_OVERLAY_PERMISSION来让动态设置权限，在Activity中设置。

// MainActivity.kt
fun startWindow(view: View?) {
    if (!Settings.canDrawOverlays(this)) {
        startActivityForResult(Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:$packageName")), 0)
    } else {
        startService(Intent(this@MainActivity, FloatingWindowService::class.java))
    }
}
​
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
    super.onActivityResult(requestCode, resultCode, data)
    if (requestCode == 0) {
        if (Settings.canDrawOverlays(this)) {
            Toast.makeText(this, "悬浮窗权限授权成功", Toast.LENGTH_SHORT).show()
            startService(Intent(this@MainActivity, FloatingWindowService::class.java))
        }
    }
}

3.3 完整代码

class FloatingWindowService : Service() {
    private lateinit var windowManager: WindowManager
    private lateinit var layoutParams: WindowManager.LayoutParams
    private lateinit var tvContent: AppCompatTextView
    private lateinit var handler: Handler

    private var receiver: MyReceiver? = null
    private var floatingView: View? = null
    private val stringBuilder = StringBuilder()

    private var x = 0
    private var y = 0

    // 用来判断floatingView是否attached 到 window manager，防止二次removeView导致崩溃
    private var attached = false

    override fun onCreate() {
        super.onCreate()
        // 注册广播
        receiver = MyReceiver()
        val filter = IntentFilter()
        filter.addAction("android.intent.action.MyReceiver")
        registerReceiver(receiver, filter);

        // 获取windowManager并设置layoutParams
        windowManager = getSystemService(WINDOW_SERVICE) as WindowManager
        layoutParams = WindowManager.LayoutParams().apply {
            type = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY
            } else {
                WindowManager.LayoutParams.TYPE_PHONE
            }
            format = PixelFormat.RGBA_8888
//            format = PixelFormat.TRANSPARENT
            gravity = Gravity.START or Gravity.TOP
            flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL or WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
            width = 600
            height = 600
            x = 300
            y = 300
        }
        handler = Handler(this.mainLooper) { msg ->
            tvContent.text = msg.obj as String
            // 当文本超出屏幕自动滚动，保证文本处于最底部
            val offset = tvContent.lineCount * tvContent.lineHeight
            floatingView?.apply {
                if (offset > height) {
                    tvContent.scrollTo(0, offset - height)
                }
            }
            false
        }
    }

    override fun onBind(intent: Intent?): IBinder? {
        return null
    }

    @SuppressLint("ClickableViewAccessibility")
    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        if (Settings.canDrawOverlays(this)) {
            floatingView = LayoutInflater.from(this).inflate(R.layout.layout_show_log, null)
            tvContent = floatingView!!.findViewById(R.id.tv_log)
            floatingView!!.findViewById<AppCompatImageView>(R.id.iv_close).setOnClickListener {
                stringBuilder.clear()
                windowManager.removeView(floatingView)
                attached = false
            }
            // 设置TextView滚动
            tvContent.movementMethod = ScrollingMovementMethod.getInstance()

            floatingView!!.findViewById<FrameLayout>(R.id.layout_drag).setOnTouchListener { v, event ->
                when (event.action) {
                    MotionEvent.ACTION_DOWN -> {
                        x = event.rawX.toInt()
                        y = event.rawY.toInt()
                    }
                    MotionEvent.ACTION_MOVE -> {
                        val currentX = event.rawX.toInt()
                        val currentY = event.rawY.toInt()
                        val offsetX = currentX - x
                        val offsetY = currentY - y
                        x = currentX
                        y = currentY
                        layoutParams.x = layoutParams.x + offsetX
                        layoutParams.y = layoutParams.y + offsetY
                        windowManager.updateViewLayout(floatingView, layoutParams)
                    }
                }
                true
            }

            windowManager.addView(floatingView, layoutParams)
            attached = true
        }
        return super.onStartCommand(intent, flags, startId)
    }

    override fun onDestroy() {
        // 注销广播并删除浮窗
        unregisterReceiver(receiver)
        receiver = null
        if (attached) {
            windowManager.removeView(floatingView)
        }
    }

    inner class MyReceiver : BroadcastReceiver() {
        override fun onReceive(context: Context, intent: Intent) {
            val content = intent.getStringExtra("content") ?: ""
            stringBuilder.append(content).append("\n")
            val message = Message.obtain()
            message.what = 0
            message.obj = stringBuilder.toString()
            handler.sendMessage(message)
        }
    }
}

4. 总结

以上就是Android悬浮窗的一个简单实现方式。如果需要实现其他复杂一点的功能，比如播放视频，也可以在此基础上完成。

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