Android:AbsListView.setItemChecked() 导致 ActionMode 销毁并重新创建？

Question

如果您直接调用 AbsListView.setItemChecked()，效果很好，ActionMode 将激活并创建。

mGridView.setItemChecked(pPosition, true);

但是当你先调用View.startActionMode()，再调用AbsListView.setItemChecked()时，创建的ActionMode startActionMode() 将销毁，并通过 setItemChecked() 重新创建一个新的。

我的问题是:如何在调用 View.startActionMode() 时避免这个问题？

期待您的回复!谢谢!

Answer 1

为什么要重新创建一个新的？查看AbsListView.setItemChecked(int position, boolean value)方法的源码，可以看到如下代码:

    // Start selection mode if needed. We don't need to if we're unchecking something.
    if (value && mChoiceMode == CHOICE_MODE_MULTIPLE_MODAL && mChoiceActionMode == null) {
        if (mMultiChoiceModeCallback == null ||
                !mMultiChoiceModeCallback.hasWrappedCallback()) {
            throw new IllegalStateException("AbsListView: attempted to start selection mode " +
                    "for CHOICE_MODE_MULTIPLE_MODAL but no choice mode callback was " +
                    "supplied. Call setMultiChoiceModeListener to set a callback.");
        }
        mChoiceActionMode = startActionMode(mMultiChoiceModeCallback);
    }

这意味着如果 mChoiceActionMode == null，它将调用 startActionMode(mMultiChoiceModeCallback)，因此将重新创建一个新的 ActionMode。

如何修复？这里有一个简单的方法:使用reflect将startActionMode()创建的ActionMode赋值给AbsListView中的私有(private)字段mChoiceActionMode。

private void startActionMode() {
    // Get the field "mMultiChoiceModeCallback" instance by reflect
    AbsListView.MultiChoiceModeListener wrapperIns = null;
    try {
        Field wrapper = null;
        wrapper = AbsListView.class.getDeclaredField("mMultiChoiceModeCallback");
        wrapper.setAccessible(true);
        wrapperIns = (AbsListView.MultiChoiceModeListener) wrapper.get(mMessageGridView);
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    }
    // Start the ActionMode, but not select any item. 
    ActionMode actionMode = mMessageGridView.startActionMode(wrapperIns);
    // Assign actionMode to field "mChoiceActionMode" by reflect 
    try {
        Field mChoiceActionMode = null;
        mChoiceActionMode = AbsListView.class.getDeclaredField("mChoiceActionMode");
        mChoiceActionMode.setAccessible(true);
        mChoiceActionMode.set(mMessageGridView, actionMode);
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    }
}

为什么我们在这里使用包装器？因为 AbsListView.setMultiChoiceModeListener(MultiChoiceModeListener listener) 会把我们的 mMultiChoiceModeListener 包裹起来，所以我们不能不直接使用。