如何在CustomAdapter中对回收器视图实现LongPress？

Question

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.MenuInflater android.support.v4.app.FragmentActivity.getMenuInflater()' on a null object reference 
at onCreateActionMode

public ModalMultiSelectorCallback mDeleteMode = new ModalMultiSelectorCallback(mMultiSelector) {

        @Override
        public boolean onCreateActionMode(ActionMode actionMode, Menu menu) {
            super.onCreateActionMode(actionMode, menu);
            getActivity().getMenuInflater().inflate(R.menu.list_item_delete, menu);
            return true;
        }

context = getActivity();

customAdapter = new MyCustomAdapter(context, myArrayList);

public MyCustomAdapter(Context context, ArrayList<myArrayList> myArrayList) {
        mContext = context;
        this.myArrayList= myArrayList;
    }

@Override
        public boolean onLongClick(View v) {

            ((AppCompatActivity) mContext).startSupportActionMode(myFragment.mDeleteMode);
            myFragment.mMultiSelector.setSelected(this, true);
            return true;
        }

这将在上面的NullPointerException中结束。你知道为什么吗？

Answer 1

我猜您正在使用Big Nerd Ranch的RecycerView-MultiSelect库，并将此示例代码作为项目的基础。在此示例项目中，ModalMultiSelectorCallback对象在全局范围内被实例化。

考虑到您试图调用getactivity()，在调用片段的oncreate()方法之前，null可以是null。我将遵循以下步骤来解决此问题。

首先，使用actionmode.getmenuflater()而不是getactivity()，因为actionmode将提供上下文。接下来，创建一个用实现扩展ModalMultiSelectorCallback的类：

public class CustomMultiSelectorCallback extends ModalMultiSelectorCallback {

    public CustomMultiSelectorCallback(MultiSelector multiSelector) {
        super(multiSelector);
    }

    @Override
    public boolean onCreateActionMode(ActionMode actionMode, Menu menu) {
        super.onCreateActionMode(actionMode, menu);
        actionMode.getMenuInflater().inflate(R.menu.crime_list_item_context, menu);
        return true;
    }

    @Override
    public boolean onActionItemClicked(ActionMode actionMode, MenuItem menuItem) {
        ...
    }
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    mMultiSelector = new MultiSelector();
    mDeleteMode = new CustomMultiSelectorCallback(mMultiSelector);
}