Android实现listview滑动时渐隐渐现顶部栏实例代码

private void initListener() { 
lvList.setOnScrollChangeListener(new View.OnScrollChangeListener() { 
@Override 
public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) { 
} 
}); 
lvList.setOnScrollListener(new AbsListView.OnScrollListener() { 
@Override 
public void onScrollStateChanged(AbsListView view, int scrollState) { 
} 
@Override 
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { 
// Logger.myLog("firstVisibleItem=" + firstVisibleItem + "visibleItemCount=" + visibleItemCount + "totalItemCount=" + totalItemCount); 
Logger.myLog(getScroolY()+"top=" + gettop()); 
tvText.setAlpha(getAlphaFloat(getScroolY())); 
} 
}); 
} 
/** 
* 获取渐变透明值 
* @param dis 
* @return 
*/ 
public float getAlphaFloat(int dis){ 
int step = 5000; 
if(dis == 0){ 
return 0.0f; 
} 
if(dis < step){ 
return (float)(dis * (1.0/step)); 
}else{ 
return 1.0f; 
} 
} 
/** 
* 获取上滑的距离 
* @return distance 
*/ 
public int getScroolY(){ 
View c = lvList.getChildAt(0); 
if(null == c){ 
return 0; 
} 
int firstVisiblePosition = lvList.getFirstVisiblePosition(); 
int top = c.getTop(); 
/** 
* 声明一下，这里测试得到的top值始终是listview条目中显示的第一条距离顶部的距离， 
* 而这个在坐标中的表示是一个负数，所以需要对其取一个绝对值 
*/ 
return firstVisiblePosition * c.getHeight() + Math.abs(top); 
} 
/** 
* 获取首条距离顶部的高度 
* @return distance top 
*/ 
private int gettop(){ 
View c = lvList.getChildAt(0); 
if(null == c){ 
return 0; 
} 
return c.getTop(); 
}