有些项目在列表视图onScroll方法无效 [英] Some items are null in listview onScroll method

问题描述

我有一个ListView和我重写它的onScroll事件，以便我可以在列表视图中第一个可见项目的文本的第一个字符。我的code是如下：

I have a listview and I override the onScroll event for it so that I can get the first character of the text on the first visible item of the listview. My code is as follows:

@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
    //
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
           int visibleItemCount, int totalItemCount) {
    ListView caller = (ListView) view;
    View v = caller.getChildAt(firstVisibleItem);
    if(v instanceof TextView){
        TextView tv = (TextView) v;
        if(tv != null){
            String sInitial = tv.getText().toString(); 
            sInitial = Character.toString(sInitial.charAt(0));

            TextView tvPager = (TextView) findViewById(R.id.tvPager);
            tvPager.setText(sInitial);
        }
    }
}

在该FirstVisibleItem变量是从0到12（以precise），我的视图V不为空，我可以得到它的文本。但是，当它超过12，我的v是已空。我的项目是不是12路多，因此不能为空。

When the FirstVisibleItem variable is from 0 to 12(to be precise), my View v is not null and I can get the text of it. But when it goes beyond 12, my v is already null. My items are way more than 12 so it shouldn't be null.

是不是有什么毛病我code？还是有更好的方法做我想要什么？
在此先感谢！

Is there something wrong with my code? Or are there better way doing what I want? Thanks in advance!

推荐答案

在Android的ListView回收列表中的项目的时候都没有显示在屏幕上。因此，任何不可见为null。

An android listview recycles "items" in the list when they are not visible on the screen. So anything that is not visible will be null.

http://commonsware.com/Android/excerpt.pdf

这篇关于有些项目在列表视图onScroll方法无效的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！