java - 当到达 GridView 末尾时无限调用 "onScroll"

Question

我发现以下代码可以在到达 gridview 末尾时执行某些操作:

    GridView gridview = (YMAnimatedGridview) v.findViewById(R.id.my_gridview);
    gridview.setAdapter(adapter);
    final View footerView = mainView
            .findViewById(R.id.my_grid_footer_view);
    gridview.setOnScrollListener(new GridView.OnScrollListener() {

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {

            if (firstVisibleItem + visibleItemCount == totalItemCount) {

                // last item in grid is on the screen, show footer:
                fetchMoreItems();

            } 
        }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
    }

问题是，当我到达 gridView 的末尾时，会连续调用此方法。

private void fetchMoreItems() {
    Log.i(LOG_TAG, "Reached the end of grid view"); //for debbug purposes
    Integer lastIndex = thumbnails.length; //This is a Bitmap array with the data I'm alredy showing
    Cursor cursor = getData();
    thumbnails = concat(thumbnails, new Bitmap[30]);
    Integer lastIndexToRun = Math.min(30, cursor.getCount() - lastIndex);
    for(int j = 0; j < lastIndexToRun; j++) {
        Integer i = j + lastIndex;
        cursor.moveToPosition(i);
        thumbnails[i] = getThumbnail(i);
    }
    adapter.notifyDataSetChanged(); //This is the adapter used to fill the gridview
    cursor.close();
}

我认为我的错误应该是在 fetchMoreItems() 方法中，但由于这是我第一次使用 GridView，所以我不确定

Answer 1

您需要避免多次调用该方法，如下所示:

private int beforeLastItem;

@Override
public void onScroll(AbsListView view, int firstVisibleItem,
                     int visibleItemCount, int totalItemCount) {
    final int lastItem = firstVisibleItem + visibleItemCount;
    if (lastItem == totalItemCount) {
        // last item in grid is on the screen, show footer:
        if (beforeLastItem != lastItem){ //to avoid multiple calls for the last item
            fetchMoreItems();
            beforeLastItem = lastItem;
        }
    } else {
        beforeLastItem = lastItem;
    }
}