Android实现美团、大众点评的购买悬浮效果（ScrollView滚动监听）

<&＃63;xml version="1.0" encoding="UTF-8"&＃63;> 
 
 
  
 
 

package com.example.meituandemo; 
 
import android.content.Context; 
import android.os.Handler; 
import android.util.AttributeSet; 
import android.view.MotionEvent; 
import android.widget.ScrollView; 
/** 
 * 博客地址:http://blog.csdn.net/xiaanming 
 * 
 * @author xiaanming 
 * 
 */ 
public class MyScrollView extends ScrollView { 
 private OnScrollListener onScrollListener; 
 /** 
  * 主要是用在用户手指离开MyScrollView，MyScrollView还在继续滑动，我们用来保存Y的距离，然后做比较 
  */ 
 private int lastScrollY; 
  
 public MyScrollView(Context context) { 
  this(context, null); 
 } 
  
 public MyScrollView(Context context, AttributeSet attrs) { 
  this(context, attrs, 0); 
 } 
 
 public MyScrollView(Context context, AttributeSet attrs, int defStyle) { 
  super(context, attrs, defStyle); 
 } 
  
 /** 
  * 设置滚动接口 
  * @param onScrollListener 
  */ 
 public void setOnScrollListener(OnScrollListener onScrollListener) { 
  this.OnScrollListener= onScrollListener; 
 } 
 
 
 /** 
  * 用于用户手指离开MyScrollView的时候获取MyScrollView滚动的Y距离，然后回调给onScroll方法中 
  */ 
 private Handler handler = new Handler() { 
 
  public void handleMessage(android.os.Message msg) { 
   int scrollY = MyScrollView.this.getScrollY(); 
    
   //此时的距离和记录下的距离不相等，在隔5毫秒给handler发送消息 
   if(lastScrollY != scrollY){ 
    lastScrollY = scrollY; 
    handler.sendMessageDelayed(handler.obtainMessage(), 5); 
   } 
   if(onScrollListener != null){ 
    onScrollListener.onScroll(scrollY); 
   } 
    
  }; 
 
 }; 
 
 /** 
  * 重写onTouchEvent， 当用户的手在MyScrollView上面的时候， 
  * 直接将MyScrollView滑动的Y方向距离回调给onScroll方法中，当用户抬起手的时候， 
  * MyScrollView可能还在滑动，所以当用户抬起手我们隔5毫秒给handler发送消息，在handler处理 
  * MyScrollView滑动的距离 
  */ 
 @Override 
 public boolean onTouchEvent(MotionEvent ev) { 
  if(onScrollListener != null){ 
   onScrollListener.onScroll(lastScrollY = this.getScrollY()); 
  } 
  switch(ev.getAction()){ 
  case MotionEvent.ACTION_UP: 
    handler.sendMessageDelayed(handler.obtainMessage(), 5); 
   break; 
  } 
  return super.onTouchEvent(ev); 
 } 
 
 
 /** 
  * 
  * 滚动的回调接口 
  * 
  * @author xiaanming 
  * 
  */ 
 public interface OnScrollListener{ 
  /** 
   * 回调方法， 返回MyScrollView滑动的Y方向距离 
   * @param scrollY 
   *    、 
   */ 
  public void onScroll(int scrollY); 
 } 
  
  
 
} 

package com.example.meituandemo; 
 
import android.app.Activity; 
import android.content.Context; 
import android.graphics.PixelFormat; 
import android.os.Bundle; 
import android.view.Gravity; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.WindowManager; 
import android.view.WindowManager.LayoutParams; 
import android.widget.LinearLayout; 
import com.example.meituandemo.MyScrollView.OnScrollListener; 
/** 
 * 博客地址:http://blog.csdn.net/xiaanming 
 * 
 * @author xiaanming 
 * 
 */ 
public class MainActivity extends Activity implements OnScrollListener{ 
 private MyScrollView myScrollView; 
 private LinearLayout mBuyLayout; 
 private WindowManager mWindowManager; 
 /** 
  * 手机屏幕宽度 
  */ 
 private int screenWidth; 
 /** 
  * 悬浮框View 
  */ 
 private static View suspendView; 
 /** 
  * 悬浮框的参数 
  */ 
 private static WindowManager.LayoutParams suspendLayoutParams; 
 /** 
  * 购买布局的高度 
  */ 
 private int buyLayoutHeight; 
 /** 
  * myScrollView与其父类布局的顶部距离 
  */ 
 private int myScrollViewTop; 
 
 /** 
  * 购买布局与其父类布局的顶部距离 
  */ 
 private int buyLayoutTop; 
  
 
 @Override 
 protected void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.activity_main); 
   
  myScrollView = (MyScrollView) findViewById(R.id.scrollView); 
  mBuyLayout = (LinearLayout) findViewById(R.id.buy); 
   
  myScrollView.setOnScrollListener(this); 
  mWindowManager = (WindowManager) getSystemService(Context.WINDOW_SERVICE); 
  screenWidth = mWindowManager.getDefaultDisplay().getWidth(); 
 } 
 
 /** 
  * 窗口有焦点的时候，即所有的布局绘制完毕的时候，我们来获取购买布局的高度和myScrollView距离父类布局的顶部位置 
  */ 
 @Override 
 public void onWindowFocusChanged(boolean hasFocus) { 
  super.onWindowFocusChanged(hasFocus); 
  if(hasFocus){ 
   buyLayoutHeight = mBuyLayout.getHeight(); 
   buyLayoutTop = mBuyLayout.getTop(); 
    
   myScrollViewTop = myScrollView.getTop(); 
  } 
 } 
 
 
 
 /** 
  * 滚动的回调方法，当滚动的Y距离大于或者等于 购买布局距离父类布局顶部的位置，就显示购买的悬浮框 
  * 当滚动的Y的距离小于 购买布局距离父类布局顶部的位置加上购买布局的高度就移除购买的悬浮框 
  * 
  */ 
 @Override 
 public void onScroll(int scrollY) { 
  if(scrollY >= buyLayoutTop){ 
   if(suspendView == null){ 
    showSuspend(); 
   } 
  }else if(scrollY <= buyLayoutTop + buyLayoutHeight){ 
   if(suspendView != null){ 
    removeSuspend(); 
   } 
  } 
 } 
 
 
 /** 
  * 显示购买的悬浮框 
  */ 
 private void showSuspend(){ 
  if(suspendView == null){ 
   suspendView = LayoutInflater.from(this).inflate(R.layout.buy_layout, null); 
   if(suspendLayoutParams == null){ 
    suspendLayoutParams = new LayoutParams(); 
    suspendLayoutParams.type = LayoutParams.TYPE_PHONE; //悬浮窗的类型，一般设为2002，表示在所有应用程序之上，但在状态栏之下 
    suspendLayoutParams.format = PixelFormat.RGBA_8888; 
    suspendLayoutParams.flags = LayoutParams.FLAG_NOT_TOUCH_MODAL 
       | LayoutParams.FLAG_NOT_FOCUSABLE; //悬浮窗的行为，比如说不可聚焦，非模态对话框等等 
    suspendLayoutParams.gravity = Gravity.TOP; //悬浮窗的对齐方式 
    suspendLayoutParams.width = screenWidth; 
    suspendLayoutParams.height = buyLayoutHeight; 
    suspendLayoutParams.x = 0; //悬浮窗X的位置 
    suspendLayoutParams.y = myScrollViewTop; ////悬浮窗Y的位置 
   } 
  } 
   
  mWindowManager.addView(suspendView, suspendLayoutParams); 
 } 
  
  
 /** 
  * 移除购买的悬浮框 
  */ 
 private void removeSuspend(){ 
  if(suspendView != null){ 
   mWindowManager.removeView(suspendView); 
   suspendView = null; 
  } 
 } 
 
}