android 实现listview 的item 出现在屏幕有个动画效果 类似于知乎的那个app

这个是知乎1.80版本上面的一个效果，后面的版本好像砍掉了

先上图：

，很难直观的看出来，因为录gif效果比较差，listview每一个item出现在屏幕的可见范围内的时候会有一个从上而下或者从下而上的动画效果。

原理很简单的，这里也只是简单说下原理实现。

步骤：

1、复写listview

2、实现OnScrollListener接口

3、关键在这个实现函数里面public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount)

onScroll（）后面的参数

/**
	 * 当ListView滚动时触发
	 * firstVisibleItem 屏幕上显示的第一个Item的position
	 * visibleItemCount 当前屏幕显示的总个数
	 * totalItemCount   ListView的总条数
	 */
	int i=0;
	int j=0;
	@Override
	public void onScroll(AbsListView view, int firstVisibleItem,
			int visibleItemCount, int totalItemCount) {
		firstVisibleItemPosition = firstVisibleItem;
		Log.i("RefreshListView", "onScroll: " + firstVisibleItem + ", " + visibleItemCount + ", " + totalItemCount+"|_--");
		
		if(mOnRefreshListener != null && (i!=firstVisibleItem+visibleItemCount-1 || j!=firstVisibleItem)) {
			if(i<(firstVisibleItem+visibleItemCount-1)){
				mOnRefreshListener.onOutitem(firstVisibleItem+visibleItemCount-1,1);
				
				}else if(j>firstVisibleItem || j==0)
				{
					mOnRefreshListener.onOutitem(firstVisibleItem,0);//这是回调函数，当屏幕出现listview新的item，会将出的item传给activity
				
				}
		}
		j=firstVisibleItem;//保存上一次滑动可视的第一个item的position
		i=firstVisibleItem+visibleItemCount-1;//保存上一次滑动可视的最后item的position
		
		
		if((firstVisibleItem + visibleItemCount) >= totalItemCount
				&& totalItemCount > 0) {
//			Log.i("RefreshListView", "加载更多");
			isScroll2Bottom = true;
		} else {
			isScroll2Bottom = false;
		}
	}

activity 的回调函数收到这个position之后，就可以实现动画效果了

mPullRefreshListView.setOnRefreshListener(new OnRefreshListener() {

			public void onRefresh() {
				// Do work to refresh the list here.
				getSpilts(Contacts.GetSpiltTypeUp);
			}

			@Override
			public void onLoadMoring() {
				// TODO Auto-generated method stub
				getSpilts(Contacts.GetSpiltTypeDown);
			}

			@Override
			public void onOutitem(int itemNum, int from) {
				// TODO Auto-generated method stub
				System.out.println(itemNum);
				int wantedPosition = itemNum; // Whatever position you're looking for
				int firstPosition = mPullRefreshListView.getFirstVisiblePosition() ; // - mPullRefreshListView.getHeaderViewsCount() This is the same as child #0
				int wantedChild = wantedPosition - firstPosition;
				if (wantedChild < 0 || wantedChild >= mPullRefreshListView.getChildCount()) {
				  Log.w("tag", "Unable to get view for desired position, because it's not being displayed on screen.");
				  return;
				}
				// Could also check if wantedPosition is between listView.getFirstVisiblePosition() and listView.getLastVisiblePosition() instead.
				View view = mPullRefreshListView.getChildAt(wantedChild);
				
				Animation procAnim = null;
				if(from == 1)
				{
					procAnim=new TranslateAnimation(0, 0,20,0);
				}else
				{
					procAnim=new TranslateAnimation(0, 0,-20,0);
				}
				procAnim.setDuration(700);
				procAnim.setFillAfter(true);
				view.startAnimation(procAnim);
				
			}
		});