Android悬浮窗的简单实现

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"?>
<LinearLayoutxmlns: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"><FrameLayoutandroid:id="@+id/layout_drag"android:layout_width="match_parent"android:layout_height="15dp"android:background="#dddddd"><androidx.appcompat.widget.AppCompatImageViewandroid: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.AppCompatTextViewandroid: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WindowManagerwindowManager = getSystemService(WINDOW_SERVICE) as WindowManagerlayoutParams = 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.TOPflags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL or WindowManager.LayoutParams.FLAG_NOT_FOCUSABLEwidth = 600height = 600x = 300y = 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 = 0override 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 - xval offsetY = currentY - yx = currentXy = currentYlayoutParams.x = layoutParams.x + offsetXlayoutParams.y = layoutParams.y + offsetY// 更新floatingViewwindowManager.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UIval message = Message.obtain()message.what = 0message.obj = contenthandler.sendMessage(message)}
}val handler = Handler(this.mainLooper) { msg ->tvContent.text = msg.obj as Stringfalse
}

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: WindowManagerprivate lateinit var layoutParams: WindowManager.LayoutParamsprivate lateinit var tvContent: AppCompatTextViewprivate lateinit var handler: Handlerprivate var receiver: MyReceiver? = nullprivate var floatingView: View? = nullprivate val stringBuilder = StringBuilder()private var x = 0private 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 = falseoverride 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layoutParamswindowManager = getSystemService(WINDOW_SERVICE) as WindowManagerlayoutParams = 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.TRANSPARENTgravity = Gravity.START or Gravity.TOPflags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL or WindowManager.LayoutParams.FLAG_NOT_FOCUSABLEwidth = 600height = 600x = 300y = 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.lineHeightfloatingView?.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 - xval offsetY = currentY - yx = currentXy = currentYlayoutParams.x = layoutParams.x + offsetXlayoutParams.y = layoutParams.y + offsetYwindowManager.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 = nullif (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 = 0message.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。