Android 开启悬浮窗
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开启全局的悬浮窗（即覆盖在所有 Activity 上的悬浮窗）需要使用 Application 的 Window ，即使用 Application Context获取 WindowManager。
WindowManager manager = (WindowManager) applicationContext.getSystemService(WINDOW_SERVICE);
如果使用 Activity Context 获取 WindowManager，则悬浮窗只能显示在当前 Activity。
WindowManager manager = (WindowManager) activityContext.getSystemService(WINDOW_SERVICE);
申请权限方式开启悬浮窗:
WindowManager manager = (WindowManager) context.getSystemService(WINDOW_SERVICE);
TextView textView = new TextView(MainActivity.this);
textView.setText("悬浮窗测试");
WindowManager.LayoutParams lp = new WindowManager.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT,
WindowManager.LayoutParams.TYPE_SYSTEM_ALERT,
WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
| WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON,
PixelFormat.TRANSLUCENT
| WindowManager.LayoutParams.FIRST_SYSTEM_WINDOW);
manager.addView(textView, lp);
添加权限：
<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
不需权限开启悬浮窗
将上面代码中的 WindowManager.LayoutParams.TYPE_SYSTEM_ALERT 改成 WindowManager.LayoutParams.TYPE_TOAST 即可。
WindowManager manager = (WindowManager) context.getSystemService(WINDOW_SERVICE);
TextView textView = new TextView(MainActivity.this);
textView.setText("悬浮窗测试");
WindowManager.LayoutParams lp = new WindowManager.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT,
WindowManager.LayoutParams.TYPE_TOAST,
WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
| WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON,
PixelFormat.TRANSLUCENT
| WindowManager.LayoutParams.FIRST_SYSTEM_WINDOW);
manager.addView(textView, lp);