WindowManager 实现悬浮窗-拖拽！

声明权限：
获得 WindowManager
mWindowManager = (WindowManager) getApplicationContext().getSystemService(Context.WINDOW_SERVICE);
生成LayoutParams

mLayoutParams = new WindowManager.LayoutParams(
WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.WRAP_CONTENT, 2099,
WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
        | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
        | WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED,
PixelFormat.TRANSPARENT);

WindowManager.LayoutParams 构参

构造参数：LayoutParams(int w, int h, int _type, int _flags, int _format)
_type：

• 应用window的层级范围：1-99
• 子window的层级范围：1000-1999
• 系统window的层级范围：2000-2999

_flags：

• FLAG_NOT_TOUCH_MODAL：自己区域内事件自己处理，区域外事件传递给底层window处理。一般默认开启。否则其他window无法获得事件
• FLAG_NOT_FOCUSABLE：window不需要获取焦点，把焦点传递给下层window。
• FLAG_SHOW_WHEN_LOCKED：可以显示在锁屏界面上。

示例代码

public class MainActivity extends AppCompatActivity implements View.OnTouchListener {

    private WindowManager mWindowManager;
    private ImageView mImageView;
    private WindowManager.LayoutParams mLayoutParams;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        mWindowManager = (WindowManager) getApplicationContext().getSystemService(Context.WINDOW_SERVICE);
        mImageView = new ImageView(this);
        mImageView.setBackgroundResource(R.mipmap.ic_launcher);
        mLayoutParams = new WindowManager.LayoutParams(
                WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.WRAP_CONTENT, 2099,
                WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL
                        | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
                        | WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED,
                PixelFormat.TRANSPARENT);
        mLayoutParams.type = WindowManager.LayoutParams.TYPE_SYSTEM_ERROR;
        mLayoutParams.gravity = Gravity.TOP | Gravity.LEFT;
        mLayoutParams.x = 0;
        mLayoutParams.y = 300;
        mImageView.setOnTouchListener(this);
        mWindowManager.addView(mImageView, mLayoutParams);
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        int rawX = (int) event.getRawX();
        int rawY = (int) event.getRawY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_MOVE: {
                mLayoutParams.x = rawX;
                mLayoutParams.y = rawY;
                mWindowManager.updateViewLayout(mImageView, mLayoutParams);
                break;
            }
            default:
                break;
        }
        return false;
    }

    @Override
    protected void onDestroy() {
        try {
            mWindowManager.removeView(mImageView);
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        }
        super.onDestroy();
    }

}