Question

在Activity中，如何访问Expandable ListView的第一个组视图？

这是我正在做的事情：

public int getFirstVisibleGroup() {
        LogUtil.i(TAG, "getFirstVisibleGroup called");
        int firstVis = listView.getFirstVisiblePosition();
        LogUtil.i(TAG, "firstVis = " + firstVis);
        long packedPosition = listView.getExpandableListPosition(firstVis);
        LogUtil.i(TAG, "packedPosition = " + packedPosition);
        LogUtil.i(TAG, "firstVisibleGroup = " + ExpandableListView.getPackedPositionGroup(packedPosition));
        return ExpandableListView.getPackedPositionGroup(packedPosition);
    }

    public View getGroupView(ExpandableListView listView, int groupPosition) {
        LogUtil.i(TAG, "getGroupView called");
        int flatPosition = listView.getFlatListPosition(groupPosition);
        LogUtil.i(TAG, "flatPosition = " + flatPosition);
        int first = getFirstVisibleGroup();
        LogUtil.i(TAG, "first = " + first);
        LogUtil.i(TAG, "returning child at position " + (flatPosition - first));
        return listView.getChildAt(flatPosition - first);
    }

我称之为：

View view = getGroupView(listView, 0);

最终它变为listView.getChildAt(0)。返回的view为空。

这样做的正确方法是什么？

Answer 1

所有基于适配器的视图（ListView，GridView，RecyclerView）仅在将视图布置在屏幕上后才将视图添加到自身。这样他们就可以计算出适当的大小并查询足够的子视图。

因此，在onCreate期间，您永远不会有任何观点。这意味着，如果您想要与其某些子视图进行交互，则必须在以后进行。

一种合适的方法是使用OnPreDraw侦听器。这是在系统在视图上调用draw(canvas)之前。例如：

public MyActivity extends Activity implements ViewTreeObserver.OnPreDrawListener {

    @Override
    public void onCreate(bundle){
        ... build your layout and your listview

        // during onCreate you add a PreDrawListener
        rootView.getViewTreeObserver().addOnPreDrawListener(this);
    }

    @Override
    public void onPreDraw() {

        ... do your logic here !!!


        rootView.getViewTreeObserver().removeOnPreDrawListener(this); // remove itself, you only need the fist pass
        return true; // must return true, or else the system won't draw anything.
    }

}

获取第一组可扩展ListView的视图句柄

1 个答案: