如何实现Android浮动窗口

 package com.spreadst.floatwindow;
 import android.app.Service;
 import android.content.Context;
 import android.content.Intent;
 import android.graphics.PixelFormat;
 import android.os.IBinder;
 import android.util.Log;
 import android.view.Gravity;
 import android.view.LayoutInflater;
 import android.view.MotionEvent;
 import android.view.View;
 import android.view.WindowManager;

 public class FloatWindowService extends Service {

  private static final TAG = "FloatWindowService";

  private WindowManager mWindowManager;
  private WindowManager.LayoutParams mLayoutParams;
  private LayoutInflater mLayoutInflater;
  private View mFloatView;
  private int mCurrentX;
  private int mCurrentY;
  private static int mFloatViewWidth = 50;
  private static int mFloatViewHeight = 80;
  @Override
  public void onCreate() {
    // TODO Auto-generated method stub
    super.onCreate();
    //初始化WindowManager对象和LayoutInflater对象
    mWindowManager = (WindowManager) getApplicationContext().getSystemService(Context.WINDOW_SERVICE);
    mLayoutInflater = LayoutInflater.from(this);
  }
  @Override
  public void onStart(Intent intent, int startId) {
    // TODO Auto-generated method stub
    super.onStart(intent, startId);
    Log.i(TAG, "onStart()");
    createView();
  }
  private void createView() {
    // TODO Auto-generated method stub
    //加载布局文件
    mFloatView = mLayoutInflater.inflate(R.layout.main, null);
    //为View设置监听，以便处理用户的点击和拖动
    mFloatView.setOnTouchListener(new OnFloatViewTouchListener());
    /*为View设置参数*/
    mLayoutParams = new WindowManager.LayoutParams();
    //设置View默认的摆放位置
    mLayoutParams.gravity = Gravity.LEFT | Gravity.TOP;
    //设置window type
    mLayoutParams.type = WindowManager.LayoutParams.TYPE_PHONE;
    //设置背景为透明
    mLayoutParams.format = PixelFormat.RGBA_8888;
    //注意该属性的设置很重要，FLAG_NOT_FOCUSABLE使浮动窗口不获取焦点,若不设置该属性，屏幕的其它位置点击无效，应为它们无法获取焦点
    mLayoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
    //设置视图的显示位置，通过WindowManager更新视图的位置其实就是改变(x,y)的值
    mCurrentX = mLayoutParams.x = 50;
    mCurrentY = mLayoutParams.y = 50;
    //设置视图的宽、高
    mLayoutParams.width = 100;
    mLayoutParams.height = 100;
    //将视图添加到Window中
    mWindowManager.addView(mFloatView, mLayoutParams);
  }
  /*由于直接startService(),因此该方法没用*/
  @Override
  public IBinder onBind(Intent intent) {
    // TODO Auto-generated method stub
    return null;
  }
  /*该方法用来更新视图的位置，其实就是改变(LayoutParams.x,LayoutParams.y)的值*/
  private void updateFloatView() {
    mLayoutParams.x = mCurrentX;
    mLayoutParams.y = mCurrentY;
    mWindowManager.updateViewLayout(mFloatView, mLayoutParams);
  }
  /*处理视图的拖动，这里只对Move事件做了处理，用户也可以对点击事件做处理，例如：点击浮动窗口时，启动应用的主Activity*/
  private class OnFloatViewTouchListener implements View.OnTouchListener {
    @Override
    public boolean onTouch(View v, MotionEvent event) {
      // TODO Auto-generated method stub
      Log.i(TAG, "mCurrentX: " + mCurrentX + ",mCurrentY: "
          + mCurrentY + ",mFloatViewWidth: " + mFloatViewWidth
          + ",mFloatViewHeight: " + mFloatViewHeight);
      /*
       * getRawX(),getRawY()这两个方法很重要。通常情况下，我们使用的是getX(),getY()来获得事件的触发点坐标，
       * 但getX(),getY()获得的是事件触发点相对与视图左上角的坐标；而getRawX(),getRawY()获得的是事件触发点
       * 相对与屏幕左上角的坐标。由于LayoutParams中的x,y是相对与屏幕的，所以需要使用getRawX(),getRawY()。
       */
      mCurrentX = (int) event.getRawX() - mFloatViewWidth;
      mCurrentY = (int) event.getRawY() - mFloatViewHeight;
      int action = event.getAction();
      switch (action) {
      case MotionEvent.ACTION_DOWN:
        break;
      case MotionEvent.ACTION_MOVE:
        updateFloatView();
        break;
      case MotionEvent.ACTION_UP:
        break;
      }
      return true;
    }
  }
 }

private String getTopActivity(Context context) {
   //获取ActivityManager对象
   ActivityManager manager = (ActivityManager)getSystemService(ACTIVITY_SERVICE) ;
   /*
   * 拿到当前正在运行的Task列表，该列表按照最近使用的时间顺序排列，其中的参数表示需要返回的最大列表项数目。
   * 这里我们只需要拿到处于onResume状态的Activity所在的Task。
   */
   List<RunningTaskInfo> runningTaskInfos = manager.getRunningTasks(1) ;
   if(runningTaskInfos != null) {
     //拿到该task中的栈顶Activity
     return (runningTaskInfos.get(0).topActivity).toString() ;
   } else {
     return null;
   }
 }