手机悬浮窗

全局悬浮窗在许多应用中都能见到，点击Home键，小窗口仍然会在屏幕上显示。如微信视频，360软件清理等等

添加权限

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"
        tools:ignore="ProtectedPermissions" />

当API Level>=23的时候就要动态的申请权限了，判断是否能够绘制悬浮窗：

Settings.canDrawOverlays(this)

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && !Settings.canDrawOverlays(this)) {
    Toast.makeText(this, "当前无权限，请授权", Toast.LENGTH_SHORT);
    Intent intent = new Intent();
    intent.setAction(Settings.ACTION_MANAGE_OVERLAY_PERMISSION);
    intent.setData(Uri.parse("package:" + getPackageName()));
    startActivityForResult(intent, 0);
}

全局的悬浮窗是通过WindowManager来绘制已达到能够全局显示的效果，而WindowManager的addView方法还需要一个WindowManager.LayoutParam对象作为参数，此处Android 8.0之后的需要适配一下：

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
      layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
   } else {
      layoutParams.type = WindowManager.LayoutParams.TYPE_PHONE;
   }

为了能够使悬浮窗脱离activity全局显示，因此这里使用Service来启动悬浮窗。 界面触发悬浮窗代码如下：

public class MainActivity extends AppCompatActivity {
    public static boolean isStart = false;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btFloatingWindow = findViewById(R.id.bt_floating_window);
        btFloatingWindow.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startFloatingService();
            }
        });
    }
    @SuppressLint("ShowToast")
    public void startFloatingService() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && !Settings.canDrawOverlays(this)) {
            Toast.makeText(this, "当前无权限，请授权", Toast.LENGTH_SHORT);
            Intent intent = new Intent();
            intent.setAction(Settings.ACTION_MANAGE_OVERLAY_PERMISSION);
            intent.setData(Uri.parse("package:" + getPackageName()));
            startActivityForResult(intent, 0);
            return;
        }
        if (!isStart) {
            startService(new Intent(MainActivity.this, FloatingService.class));
        }
    }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == 0) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && !Settings.canDrawOverlays(this)) {
                Toast.makeText(this, "授权失败", Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(this, "授权成功", Toast.LENGTH_SHORT).show();
                if (!isStart)
                    startService(new Intent(MainActivity.this, FloatingService.class));
            }
        }
    }
}

创建悬浮窗权限

public class FloatingService extends Service {
    private WindowManager windowManager;
    private WindowManager.LayoutParams layoutParams;
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        showFloatingWindow();
        return super.onStartCommand(intent, flags, startId);
    }
    @SuppressLint("InflateParams")
    private void showFloatingWindow() {
        MainActivity.isStart = true;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && Settings.canDrawOverlays(this)) {
            // 获取WindowManager服务
            windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
            // 设置LayoutParam
            layoutParams = new WindowManager.LayoutParams();
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
            } else {
                layoutParams.type = WindowManager.LayoutParams.TYPE_PHONE;
            }
            layoutParams.format = PixelFormat.RGBA_8888;
            layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
            //宽高自适应
            layoutParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
            layoutParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
            //显示的位置
            layoutParams.x = 300;
            layoutParams.y = 300;
            // 新建悬浮窗控件
            View view = LayoutInflater.from(this).inflate(R.layout.float_window, null);
            view.setOnTouchListener(new FloatingOnTouchListener());
            // 将悬浮窗控件添加到WindowManager
            windowManager.addView(view, layoutParams);
        }
    }
    private class FloatingOnTouchListener implements View.OnTouchListener {
        private int x;
        private int y;
        @SuppressLint("ClickableViewAccessibility")
        @Override
        public boolean onTouch(View view, MotionEvent event) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    x = (int) event.getRawX();
                    y = (int) event.getRawY();
                    break;
                case MotionEvent.ACTION_MOVE:
                    int nowX = (int) event.getRawX();
                    int nowY = (int) event.getRawY();
                    int movedX = nowX - x;
                    int movedY = nowY - y;
                    x = nowX;
                    y = nowY;
                    layoutParams.x = layoutParams.x + movedX;
                    layoutParams.y = layoutParams.y + movedY;
                    // 更新悬浮窗控件布局
                    windowManager.updateViewLayout(view, layoutParams);
                    break;
                default:
                    break;
            }
            return false;
        }
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        MainActivity.isStart = false;
    }
}