片段：尽管使用 onAttach()，但方向改变后 onTextChanged null 内的回调

Question

我的片段总是抛出

java.lang.NullPointerException: Attempt to invoke interface method 'void FragmentClass$InputCallbacks.OnTextChanged(java.lang.CharSequence)' on a null object reference

因为行：

UserInput.addTextChangedListener(new TextWatcher() {
            @Override
            public void afterTextChanged(Editable s) {
            }

            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                mListener.OnTextChanged(s);
            }
        });

我对 mListener 的其他用途不是抛出任何东西。我想这是因为使用了 new Textwatcher(){....} 但我没有足够的经验自己解决这个问题:-/

整个class抛出错误：

public class ToolbarInputOneAddress extends Fragment {
    private InputCallbacks mListener;

    public ToolbarInputOneAddress() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View v = inflater.inflate(R.layout.toolbar_input_one_address, container, false);
        Address address = mListener.getAddress();
        EditText UserInput = (EditText) v.findViewById(R.id.InputField);

        if (address != null) {
            StringBuilder Sb = new StringBuilder();
            UserInput.setText(SuggestAddresses.createFormattedAddressFromAddress(address, Sb));
        }
        UserInput.addTextChangedListener(new TextWatcher() {
            @Override
            public void afterTextChanged(Editable s) {
            }

            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                mListener.OnTextChanged(s);
            }
        });

        ImageButton ReturnButton = (ImageButton) v.findViewById(R.id.btn_navigation_drawer_back);
        ReturnButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mListener.onReturnButtonClicked();
            }
        });

        return v;
    }


    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            mListener = (InputCallbacks) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement InputCallbacks");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public interface InputCallbacks {
        void OnTextChanged(CharSequence s);

        void onReturnButtonClicked();

        Address getAddress();
    }
}

Answer 1

我想我解决了。我在像这样的组中的片段中声明我的回调

public interface $Callbacks {
        void $Callback1(String s);
        void $Callback2();
        Address $Callback2();
    }

原来我定义了多个同名的回调组。我认为这没问题，因为我在 activity.

中用 implements 明确说明了这一点

自从我将回调组名称更改为不同的名称后，我不再获得 NPE：

长话短说：

我变了

implements $fragment1.callbacks $fragment2.callbacks $fragment3.callbacks

到

implements $fragment1.f1callbacks $fragment2.f2callbacks $fragment3.f3callbacks

在我的 activity 实现所述片段回调中

片段：尽管使用 onAttach()，但方向改变后 onTextChanged null 内的回调

Fragment: Callback inside onTextChanged null after orientation change despite using onAttach()

android

callback

nullpointerexception

orientation-changes

android-fragments