Android悬浮窗及其拖动事件

主页面布局很简单，只有一个RelativelyLayout

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    android:id="@+id/rl_content"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="example.floatingviewtest.MainActivity">
</RelativeLayout>

悬浮窗中只有一个TextView

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content">

    <TextView
        android:id="@+id/tv_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="这是一个悬浮TextView"
        android:paddingTop="30dp"
        android:paddingBottom="30dp"
        android:background="@color/colorPrimary"
        android:textSize="15sp"/>

</LinearLayout>

主界面代码

public class MainActivity extends AppCompatActivity {
	private static final String TAG = "MainActivity";
	/**
	 * 获取sdk版本号
	 */
	private static final int SDKVERSION = Build.VERSION.SDK_INT;
	/**
	 * 窗口管理器
	 */
	private WindowManager windowManager;
	/**
	 * 浮动按钮布局
	 */
	private View floatingButtonView;
	/**
	 * 浮动按钮布局参数
	 */
	private WindowManager.LayoutParams floatingButtonParams;
	/**
	 * 顶部状态栏高度
	 */
	private int top;
	/**
	 * 浮动窗原始位置
	 */
	private float startPositionX = 0;
	private float startPositionY = 0;
	/**
	 * 屏幕宽高
	 */
	private int contentWidth;
	private int contentHeight;

	private float lastX;
	private float lastY;
	private float mTouchStartX;
	private float mTouchStartY;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);

		initFloatingButton();
	}

	private void initFloatingButton() {
		//浮动按钮布局
		floatingButtonView = LayoutInflater.from(this).inflate(R.layout.floating_view, null);

		floatingButtonParams = new WindowManager.LayoutParams();
		if (SDKVERSION >= 19) {
			floatingButtonParams.type = WindowManager.LayoutParams.TYPE_TOAST;
		} else {
			floatingButtonParams.type = WindowManager.LayoutParams.TYPE_SYSTEM_ALERT;
		}
		floatingButtonParams.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL | WindowManager.LayoutParams
				.FLAG_NOT_FOCUSABLE;
		floatingButtonParams.format = PixelFormat.TRANSLUCENT;
		floatingButtonParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
		floatingButtonParams.height = WindowManager.LayoutParams.WRAP_CONTENT;

		floatingButtonParams.gravity = Gravity.TOP| Gravity.LEFT;
		floatingButtonParams.x = 0;
		floatingButtonParams.y = 0;

		Log.d(TAG, "initFloatingButton: " + floatingButtonParams.x + "  " + floatingButtonParams.y);
		windowManager.addView(floatingButtonView, floatingButtonParams);
		floatingButtonView.setOnTouchListener(new View.OnTouchListener() {

			@Override
			public boolean onTouch(View v, MotionEvent event) {
				lastX = event.getRawX();
				lastY = event.getRawY() - top;
				switch (event.getActionMasked()) {
					case MotionEvent.ACTION_DOWN:
						mTouchStartX = event.getX();
						mTouchStartY = event.getY();
						//记录悬浮窗原始位置
						startPositionX = floatingButtonParams.x;
						startPositionY = floatingButtonParams.y;
						Log.d(TAG, "onTouch  down  : m  " + mTouchStartX + "   " + mTouchStartY);
						Log.d(TAG, "onTouch  down  : last  " + lastX + "   " + lastY);
						Log.d(TAG, "onTouch  down  : start  " + startPositionX + "   " + startPositionY);
						Log.d(TAG, "onTouch  down  : Params  " + floatingButtonParams.x + "  " + floatingButtonParams
								.y);
						break;
					case MotionEvent.ACTION_MOVE:
						//计算新的位置
						floatingButtonParams.x = (int) (lastX - mTouchStartX);
						floatingButtonParams.y = (int) (lastY - mTouchStartY);

						//如果原始位置在中间，所以需要减去屏幕宽高的一半
//						floatingButtonParams.x = (int) (lastX - mTouchStartX - contentWidth / 2);
//						floatingButtonParams.y = (int) (lastY - mTouchStartY - contentHeight / 2);

						Log.d(TAG, "onTouch  move  : m  " + mTouchStartX + "   " + mTouchStartY);
						Log.d(TAG, "onTouch  move  : last  " + lastX + "   " + lastY);
						Log.d(TAG, "onTouch  move  : start  " + startPositionX + "   " + startPositionY);
						Log.d(TAG, "onTouch  move  : Params  " + floatingButtonParams.x + "  " + floatingButtonParams
								.y);
//
						windowManager.updateViewLayout(floatingButtonView, floatingButtonParams);
						break;
					case MotionEvent.ACTION_UP:
						Log.d(TAG, "onTouch  up  : m  " + mTouchStartX + "   " + mTouchStartY);
						Log.d(TAG, "onTouch  up  : last  " + lastX + "   " + lastY);
						Log.d(TAG, "onTouch  up  : start  " + startPositionX + "   " + startPositionY);
						Log.d(TAG, "onTouch  up  : Params  " + floatingButtonParams.x + "  " + floatingButtonParams.y);
						if (Math.abs(floatingButtonParams.x - startPositionX) < 20 && Math.abs(floatingButtonParams.y
								- startPositionY) < 20) {
							Toast.makeText(MainActivity.this, "click", Toast.LENGTH_LONG);
						}
						break;
				}
				return false;
			}
		});
	}

	@Override
	public void onWindowFocusChanged(boolean hasFocus) {
		super.onWindowFocusChanged(hasFocus);

		//获取整个布局的宽高
		Point size = new Point();
		windowManager.getDefaultDisplay().getSize(size);
		contentWidth = size.x;
		contentHeight = size.y;
		//下面这两个方法已经不建议使用了
//		windowManager.getDefaultDisplay().getWidth();
//		windowManager.getDefaultDisplay().getHeight();
		Rect rect = new Rect();
		// /取得整个视图部分,注意，如果你要设置标题样式，这个必须出现在标题样式之后，否则会出错
		getWindow().getDecorView().getWindowVisibleDisplayFrame(rect);
		top = rect.top;//状态栏的高度，所以rect.height,rect.width分别是系统的高度的宽度
		Log.d(TAG, "onWindowFocusChanged: " + contentWidth + "   " + contentHeight + "   " + top);
	}
}

以上代码主要参考了这篇博客
【【Android Demo】悬浮窗体实现】http://www.cnblogs.com/yc-755909659/p/4281214.html。
这篇博客【android悬浮窗口的实现】http://blog.csdn.net/stevenhu_223/article/details/8504058也是关于悬浮窗的，里面有源码分析，讲的更深入一些，还没来得及学习。

但是上述代码有点问题，如果将悬浮窗的初始位置设为Gravity.CENTER，在拖动的最开始会有个抖动。如果将主题设为没有title的主题，然后出去界面的宽高，在拖动的时候减去宽高的一半，则没有抖动。可是加上有title的主题后，会有微小的抖动。这一bug暂未修复。

为什么悬浮窗的属性要设置成TYPE_TOAST，请看这里

1、使用 type 值为 WindowManager.LayoutParams.TYPE_PHONE 和 WindowManager.LayoutParams.TYPE_SYSTEM_ALERT 需要申请 android.permission.SYSTEM_ALERT_WINDOW 权限，否则无法显示，报错：

E/AndroidRuntime: android.view.WindowManager$BadTokenException: Unable to add window android.view.ViewRoot$W@b64b5458 -- permission denied for this window type

2、type 值为 WindowManager.LayoutParams.TYPE_TOAST 显示的 System overlay view 不需要权限，即可在任何平台显示。

但仅在 API level >= 19 时可以达到目的。API level 19 以下因无法接收无法接收触摸（点击)和按键事件，故无法达到目的。

3、对于 API level < 19 的机器（MIUI除外），想要达到目的，需要:

要有 android.permission.SYSTEM_ALERT_WINDOW 权限
将 type 设置为 WindowManager.LayoutParams.TYPE_PHONE 或者 WindowManager.LayoutParams.TYPE_SYSTEM_ALERT

具体参考如下两篇博客
Android悬浮窗的小结：http://liaohuqiu.net/cn/posts/android-windows-manager/
Android悬浮窗TYPE_TOAST小结: 源码分析：http://www.jianshu.com/p/634cd056b90c