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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