android开发中如何利用listview实现一个悬浮topBar效果

package com.example.zwr.listviewfloatbardemo;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.ViewTreeObserver.OnGlobalLayoutListener;
import android.widget.ImageView;
import android.widget.LinearLayout;


/**
 * @author zhongwr
 */
public class MainActivity extends Activity implements FloatListView.OnScrollListener {
  protected static final String TAG = "FloatListView";
  /**
   * 自定义的listview
   */
  private FloatListView lvFloat;
  /**
   * listview中的headView中要悬浮的view
   */
  private LinearLayout mFloatTargetLayout;
  /**
   * 悬浮的view，跟headView的要一致
   */
  private LinearLayout mFloatTopLayout;
  private View head;

  @SuppressWarnings("deprecation")
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    lvFloat = (FloatListView) findViewById(R.id.scrollView);
    head = getLayoutInflater().inflate(R.layout.buy_layout_head, null);
    lvFloat.addHeaderView(head);
    mFloatTargetLayout = (LinearLayout) findViewById(R.id.buy);
    mFloatTopLayout = (LinearLayout) findViewById(R.id.top_buy_layout);

    lvFloat.setOnScrollListener(this);
    // 当布局的状态或者控件的可见性发生改变回调的接口:当布局都绘制好后会执行一次
    findViewById(R.id.parent_layout).getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {

      @Override
      public void onGlobalLayout() {
        // 这一步很重要，一开始让目标悬浮的view和要悬浮的view重合一起，之后悬浮view跟随一起目标view一起移动
        onScroll(lvFloat.getScrollY());
      }
    });
    lvFloat.setAdapter(new DataListAdapter(this));
  }

  @Override
  public void onScroll(int scrollY) {
    // SrcollView和这个Listview不同之处：scrolly是scrollview.getTop(),parent的坐标没变，只是手指向上滚动时就是scrollview滚出屏幕，但是top还是距离parent的距离，所以那里用max取最大值
    //listview手指向上滑动屏幕时会导致headRoot的top为负值，因为head是滚出屏幕的head部分并不是listview中item重用机制
    int headTop = head.getTop();
    if (headTop <= 0 && Math.abs(headTop) <= mFloatTargetLayout.getTop() && scrollY >= 0) {//手指向上滑动屏幕
      mFloatTopLayout.layout(0, mFloatTargetLayout.getTop() + headTop, mFloatTopLayout.getWidth(),
          mFloatTargetLayout.getTop() + headTop + mFloatTopLayout.getHeight());
    } else if (headTop == 0) {//当手指从上往下滑动屏幕到达最顶端时，但还有一段可滑行的距离放手后又回到起始位置,跟系统有关
      //此时这个listview的Top是负值所以要减去-scrolly：注这个scrollY=listview.getTop();让悬浮的Title跟随实际的title一起浮动
      mFloatTopLayout.layout(0, mFloatTargetLayout.getTop() - scrollY, mFloatTopLayout.getWidth(),
          mFloatTargetLayout.getTop() - scrollY + mFloatTopLayout.getHeight());
    } else if (headTop < 0) {//由于手指向上滑动屏幕的很快会导致title悬浮不到顶部，所以要强制其在顶部
      mFloatTopLayout.layout(0, 0, mFloatTopLayout.getWidth(),
          mFloatTopLayout.getHeight());
    }

    //这种方式会导致闪跳的现象，可以通过动画来实现
  }

}

public void onScroll(int scrollY) { 
    int mBuyLayout2ParentTop = Math.max(scrollY, mBuyLayout.getTop()); 
    mTopBuyLayout.layout(0, mBuyLayout2ParentTop, mTopBuyLayout.getWidth(), mBuyLayout2ParentTop + mTopBuyLayout.getHeight()); 
  } 

package com.example.zwr.listviewfloatbardemo;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.widget.ListView;
/**
 *
 * @author zhongwr
 *
 */
public class FloatListView extends ListView {
  private static final String TAG = "FloatListView";
  private OnScrollListener onScrollListener;
  
  public FloatListView(Context context) {
   this(context, null);
  }
  
  public FloatListView(Context context, AttributeSet attrs) {
   this(context, attrs, 0);
  }

  public FloatListView(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;
  }
 

  @Override
  protected void onSizeChanged(int w, int h, int oldw, int oldh) {
//  Log.d(TAG, "w = "+w);
//  Log.d(TAG, "h = "+h);
   super.onSizeChanged(w, h, oldw, oldh);
  }

  /**
  * 滚动时会执行
  * @param l 新的getLeft
  * @param t 新的getTop
  * @param oldl
  * @param oldt
  */
  @Override
  protected void onScrollChanged(int l, int t, int oldl, int oldt) {
   super.onScrollChanged(l, t, oldl, oldt);
//  Log.d(TAG, "onScrollChanged l = " + l + " t = " + t);
//  Log.d(TAG, "onScrollChanged oldl = " + oldl + " oldt = " + oldt);
   if (onScrollListener != null) {
     onScrollListener.onScroll(t);
   }
  }



  /**
  * 
  * 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);
  }
  
 

}