android 實現listview 的item 出現在屏幕有個動畫效果 類似於知乎的那個app

這個是知乎1.80版本上面的一個效果，後面的版本好像砍掉了

先上圖：

，很難直觀的看出來，因爲錄gif效果比較差，listview每一個item出現在屏幕的可見範圍內的時候會有一個從上而下或者從下而上的動畫效果。

原理很簡單的，這裏也只是簡單說下原理實現。

步驟：

1、複寫listview

2、實現OnScrollListener接口

3、關鍵在這個實現函數裏面public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount)

onScroll（）後面的參數

/**
	 * 當ListView滾動時觸發
	 * firstVisibleItem 屏幕上顯示的第一個Item的position
	 * visibleItemCount 當前屏幕顯示的總個數
	 * totalItemCount   ListView的總條數
	 */
	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);//這是回調函數，當屏幕出現listview新的item，會將出的item傳給activity
				
				}
		}
		j=firstVisibleItem;//保存上一次滑動可視的第一個item的position
		i=firstVisibleItem+visibleItemCount-1;//保存上一次滑動可視的最後item的position
		
		
		if((firstVisibleItem + visibleItemCount) >= totalItemCount
				&& totalItemCount > 0) {
//			Log.i("RefreshListView", "加載更多");
			isScroll2Bottom = true;
		} else {
			isScroll2Bottom = false;
		}
	}

activity 的回調函數收到這個position之後，就可以實現動畫效果了

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);
				
			}
		});