Java 无限呼唤；onScroll“；当到达栅格视图的末尾时

我发现以下代码可以在我到达gridview的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，这个方法被连续调用

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();
}

private void fetchMoreItems（）{
Log.i（Log_标记，“到达网格视图的末尾”）；//用于debbug
Integer lastIndex=thumbnails.length；//这是一个位图数组，其中包含我一直显示的数据
Cursor=getData（）；
缩略图=concat（缩略图，新位图[30]）；
整数lastIndexToRun=Math.min（30，cursor.getCount（）-lastIndex）；
对于（int j=0；j

---

我认为我的错误应该在fetchMoreItems（）方法中，但由于这是我第一次使用GridView，我不确定是否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;
    }
}

    private final boolean isFetching = false;
    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 && !isFetching) {
                isFetching = true;
                // last item in grid is on the screen, show footer:
                fetchMoreItems();

            }else{
                if(isFetching){
                    isFetching = false;
                }
            }
        }

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

---

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;
    }
}

    private final boolean isFetching = false;
    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 && !isFetching) {
                isFetching = true;
                // last item in grid is on the screen, show footer:
                fetchMoreItems();

            }else{
                if(isFetching){
                    isFetching = false;
                }
            }
        }

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

---

可以使用布尔值来防止多次调用，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;
    }
}

    private final boolean isFetching = false;
    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 && !isFetching) {
                isFetching = true;
                // last item in grid is on the screen, show footer:
                fetchMoreItems();

            }else{
                if(isFetching){
                    isFetching = false;
                }
            }
        }

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

---

您还可以在获取完成后将isFetching设置为false。

您可以使用布尔值来防止类似以下情况的多次调用：

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;
    }
}

    private final boolean isFetching = false;
    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 && !isFetching) {
                isFetching = true;
                // last item in grid is on the screen, show footer:
                fetchMoreItems();

            }else{
                if(isFetching){
                    isFetching = false;
                }
            }
        }

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

您还可以在提取完成后将isFetching设置为false