今天想做個導航欄漸變的效果，原來這種效果是通過監聽ScrollView的滾動距離實現的。由於首頁圖片較多，而且裡面還嵌套了ListView，大家都知道ListView巢狀在ScrollView中是需要計算高度然後全部顯示出來的，這樣ListView中的所有圖片就需要全部加載出來。在圖片做了快取的情況下，進入頁面還是會有明顯的卡頓。這時我就去掉了ScrollView，這個頁面只用ListView實現。

ScrollView滾動距離監控：

scrollView.setScrollViewListener(new ScrollViewListener() {
	
	@Override
	public void onScrollChanged(CustomScrollView scrollView, int x, int y,
			int oldx, int oldy) {
		// TODO Auto-generated method st
	}
});
 

http://blog.csdn.net/dacainiao007/article/details/28268395

http://my.oschina.net/u/1177694/blog/504992

這都試過了，基本都不好用。最後終於找到下面的文章：

http://www.2cto.com/kf/201507/416142.html

實現程式碼：

listview.setOnScrollListener(new OnScrollListener() {
	private SparseArray recordSp = new SparseArray(0);
	private int mCurrentfirstVisibleItem = 0;
	
	@Override
	public void onScrollStateChanged(AbsListView arg0, int arg1) {
		// TODO Auto-generated method stub
	}
	
	@Override
	public void onScroll(AbsListView arg0, int arg1, int arg2, int arg3) {
		// TODO Auto-generated method stub
		mCurrentfirstVisibleItem = arg1;
		View firstView = arg0.getChildAt(0);
		if (null != firstView) {
			ItemRecod itemRecord = (ItemRecod) recordSp.get(arg1);
			if (null == itemRecord) {
				itemRecord = new ItemRecod();
			}
			itemRecord.height = firstView.getHeight();
			itemRecord.top = firstView.getTop();
			recordSp.append(arg1, itemRecord);
			int h = getScrollY();//滾動距離
			}
		}
	}
	
	private int getScrollY() {
		int height = 0;
		for (int i = 0; i < mCurrentfirstVisibleItem; i++) {
			ItemRecod itemRecod = (ItemRecod) recordSp.get(i);
			height += itemRecod.height;
		}
		ItemRecod itemRecod = (ItemRecod) recordSp.get(mCurrentfirstVisibleItem);
		if (null == itemRecod) {
			itemRecod = new ItemRecod();
		}
		return height - itemRecod.top;
	}


	class ItemRecod {
		int height = 0;
		int top = 0;
	}
});
 

二、獲取滾動高度

public int getScrollY() {
    View c = listview.getChildAt(0);
    if (c == null) {
        return 0;
    }
    int firstVisiblePosition = listview.getFirstVisiblePosition();
    int top = c.getTop();
    return -top + firstVisiblePosition * c.getHeight() ;
}

ListView.smoothScrollBy(h, t);