ListView控件（适配器）项目可见监听器 [英] ListView (Adapter) item visibility listener

问题描述

是否有可能对每个ListView的项目可视性监听器？这样的：用户看到的项目，做一些事情。在项目被隐藏，做别的事情。

我要检查时，项进入和退出滚动以便更新第二列表。

Additionaly我的ListView可能会扩大，如：

  adapter.addAll（（收集和LT ;?延伸DBOBJECT＆GT;）事件）;
adapter.notifyDataSetChanged（）;
 

我想办法可能是使用一个全球性的监听器，检查项目，但恐怕它会被搞砸如果我添加更多的项目到ListView（上图）。我还没有与一事无成尚未

  eventList.setOnScrollListener（新OnScrollListener（）{        公共无效onScroll（AbsListView观点，诠释firstVisibleItem，诠释visibleItemCount，诠释totalItemCount）{        }        @覆盖
        公共无效onScrollStateChanged（AbsListView观点，诠释scrollState）{}
}）;
 

解决方案

您可以使用onScroll功能来计算。

  eventList.setOnScrollListener（新OnScrollListener（）{
    INT oldFirstVisibleItem = 0;
    INT oldLastVisibleItem = 0;    公共无效onScroll（AbsListView观点，诠释firstVisibleItem，诠释visibleItemCount，诠释totalItemCount）{
        如果（firstVisibleItem＆GT; oldFirstVisibleItem）{
            的for（int i = oldFirstVisibleItem; I＆LT; firstVisibleItem;我++）{
                onExit（ⅰ）;
            }
        }
        如果（firstVisibleItem＆LT; oldFirstVisibleItem）{
            的for（int i = firstVisibleItem; I＆LT; oldFirstVisibleItem;我++）{
                的OnEnter（ⅰ）;
            }
        }        INT lastVisibleItem = firstVisibleItem + visibleItemCount  -  1;
        如果（lastVisibleItem＆LT; oldLastVisibleItem）{
            的for（int i = oldLastVisibleItem + 1; I＆LT; = lastVisibleItem;我++）{
                onExit（ⅰ）;
            }
        }
        如果（lastVisibleItem＆GT; oldLastVisibleItem）{
            的for（int i = oldLastVisibleItem + 1; I＆LT; = lastVisibleItem;我++）{
                的OnEnter（ⅰ）;
            }
        }        oldFirstVisibleItem = firstVisibleItem;
        oldLastVisibleItem = lastVisibleItem;
    }    @覆盖
    公共无效onScrollStateChanged（AbsListView观点，诠释scrollState）{}
}）;公共无效的OnEnter（INT位置）{
    //处理项目进入人们的视野。
}公共无效onExit（INT位置）{
    //处理走出去的观点的项目。
}
 

Is it possible to have a visibility listener on each listview's item? Like: on user sees the item, do something. On item is hidden, do something else.

I want to check when a item "enters" or "exits" the scroll so as to update a second list.

Additionaly my ListView might expand like:

adapter.addAll(  (Collection<? extends DBObject>) events);
adapter.notifyDataSetChanged();

I think a way might be to use a global listener to check the items but I am afraid it will get messed up if I add more items to the ListView (above). I have not accomplished anything with that yet

eventList.setOnScrollListener(new OnScrollListener() {

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

        }

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

解决方案

You can use the onScroll function to calculate that.

eventList.setOnScrollListener(new OnScrollListener() {
    int oldFirstVisibleItem = 0;
    int oldLastVisibleItem = 0;

    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        if (firstVisibleItem > oldFirstVisibleItem) {
            for(int i = oldFirstVisibleItem; i < firstVisibleItem; i++) {
                onExit(i);
            }
        }
        if (firstVisibleItem < oldFirstVisibleItem) {
            for(int i = firstVisibleItem; i < oldFirstVisibleItem; i++) {
                onEnter(i);
            }
        }

        int lastVisibleItem = firstVisibleItem + visibleItemCount - 1;
        if (lastVisibleItem < oldLastVisibleItem) {
            for(int i = oldLastVisibleItem+1; i <= lastVisibleItem; i++) {
                onExit(i);
            }
        } 
        if (lastVisibleItem > oldLastVisibleItem) {
            for(int i = oldLastVisibleItem+1; i <= lastVisibleItem; i++) {
                onEnter(i);
            }
        } 

        oldFirstVisibleItem = firstVisibleItem;
        oldLastVisibleItem = lastVisibleItem;
    }

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

public void onEnter(int position) {
    // Handle an item coming into view.
}

public void onExit(int position) {
    // Handle an item going out of view.
}

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