android - 有人可以解释 descendantFocusability = afterDescendants 吗？

Question

我很难理解 descendantFocusability。非常特别afterDescendants。

有人可以给我举个例子说明什么时候有用吗？

Answer 1

在寻找 View 以获取焦点时，定义 ViewGroup 与其后代之间的关系。

必须是以下常量值之一。

+------------------------------------------------------------------------------------------+|      Constant            Value            Description                                    |+------------------------------------------------------------------------------------------+| afterDescendants           1          The ViewGroup will get focus only if               ||                                       none of its descendants want it.                   |+------------------------------------------------------------------------------------------+| beforeDescendants          0          The ViewGroup will get focus before                ||                                       any of its descendants.                            |+------------------------------------------------------------------------------------------+| blocksDescendants          2          The ViewGroup will block its descendants from      ||                                       receiving focus.                                   |+------------------------------------------------------------------------------------------+

You can check the complete example here.

The snippet is :

public void onItemSelected(AdapterView<?> parent, View view,
        int position, long id) {
    ListView listView = getListView();
    Log.d(TAG, "onItemSelected gave us " + view.toString());
    Button b = (Button) view.findViewById(R.id.button);
    EditText et = (EditText) view.findViewById(R.id.editor);
    if (b != null || et != null) {
        // Use afterDescendants to keep ListView from getting focus
        listView.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
        if(et!=null) et.requestFocus();
        else if(b!=null) b.requestFocus();
    } else {
        if (!listView.isFocused()) {
            // Use beforeDescendants so that previous selections don't re-take focus
            listView.setDescendantFocusability(ViewGroup.FOCUS_BEFORE_DESCENDANTS);
            listView.requestFocus();
        }
    }

}

根据上述代码段，afterDescendants 用于防止 listview 获得焦点，因此 EditText 或 Button 可以请求焦点。

注意:上面提供的链接已损坏。请引用我的Gist代码