Question

我正在尝试在我的片段中使用onBackPressed（），以便我可以允许用户回滚他在我的应用中导航的一堆片段。

问题在于，当我将下面的方法添加到我的片段时，它会给我错误：Method does not override method from its superclass。

@Override
public void onBackPressed() {

    android.support.v4.app.FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.popBackStack();

}

你知道为什么吗？

谢谢！

这是整个片段：

package it.bitrack.fabio.bitrack;

import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
//import android.app.Fragment;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;
import android.widget.ArrayAdapter;

import java.util.ArrayList;
import java.util.Arrays;
import android.view.KeyEvent;


/**
 * A simple {@link Fragment} subclass.
 * Activities that contain this fragment must implement the
 * {@link AssetMngtView.OnFragmentInteractionListener} interface
 * to handle interaction events.
 * Use the {@link AssetMngtView#newInstance} factory method to
 * create an instance of this fragment.
 */
public class AssetMngtView extends Fragment {
    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    View view;

    ListView assetMngtListView;
    ArrayAdapter<String> listAdapter;

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

    private OnFragmentInteractionListener mListener;

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

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment AssetMngtView.
     */
    // TODO: Rename and change types and number of parameters
    public static AssetMngtView newInstance(String param1, String param2) {
        AssetMngtView fragment = new AssetMngtView();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onBackPressed() {

        android.support.v4.app.FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.popBackStack();

    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment

        view = inflater.inflate(R.layout.fragment_asset_mngt_view, container, false);

        assetMngtListView = (ListView) view.findViewById(R.id.assetMngtListView);
        setListView();


        return view;
    }

    public void setListView() {

        String[] options = new String[]{"Bind tag & thing", "Create new thing", "Edit existent thing", "Maintain existent thing", "View things notifications"};

        ArrayList<String> optionsList = new ArrayList<String>();
        optionsList.addAll(Arrays.asList(options));

        listAdapter = new ArrayAdapter<>(getContext(), android.R.layout.simple_list_item_1, optionsList);

        assetMngtListView.setAdapter(listAdapter);
    }

    // TODO: Rename method, update argument and hook method into UI event
    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

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

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     * <p>
     * See the Android Training lesson <a href=
     * "http://developer.android.com/training/basics/fragments/communicating.html"
     * >Communicating with Other Fragments</a> for more information.
     */
    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }
}

Answer 1

要实现您想要的效果，您应该覆盖与之关联的onBackPressed()的{{1}}：

Activity

希望这会有所帮助。抱歉我的英文。

Answer 2

问题是Fragment没有public void onBackPressed()方法。

您收到错误是因为您的方法使用@Override进行了注释，但它实际上并没有覆盖超类中的任何方法。 @Override的目的恰恰就是这个目的，让你知道你认为自己超越了某些东西，但实际上，你并不是

在旁注中，你想要做的事情是不必要的。如果你按下后退按钮并且后面的堆栈中有碎片，它们将自动弹出。试试这个

public class FragmentsActivity extends AppCompatActivity {

    public static class FragmentA extends Fragment {
        @Nullable
        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
            View view = new TextView(getActivity());
            view.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
            view.setBackgroundColor(0xffff0000);    
            return view;
        }
    }

    public static class FragmentB extends Fragment {
        @Nullable
        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
            View view = new TextView(getActivity());
            view.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
            view.setBackgroundColor(0xff00ff00);    
            return view;
        }
    }

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fragments);

        FragmentManager fm = getSupportFragmentManager();
        fm.beginTransaction()
                .add(R.id.fragment_container, new FragmentA(), FragmentA.class.getSimpleName())
                .commit();

        // notice addToBackStack here
        fm.beginTransaction()
                .add(R.id.fragment_container, new FragmentB(), FragmentB.class.getSimpleName())
                .addToBackStack(FragmentB.class.getSimpleName())
                .commit();
    }
}

Answer 3

如果您想在片段中实现 onBackPressed 行为，您应该在片段的 onViewCreated 中执行此操作：

requireActivity().getOnBackPressedDispatcher().addCallback(new OnBackPressedCallback(true) {
    @Override
    public void handleOnBackPressed() {
        if (isHandlingBackPressInFragment()) {
            // Handle back press
        } else {
            // If you want to get default implementation of onBackPressed, use this
            this.remove();
            requireActivity().onBackPressed();
        }
    }
});

Answer 4

使用onBackPressed（）方法并在Activity类中调用popBackStack（），而不是在片段中调用

Answer 5

我很抱歉，如果我错过了解或者我错过了什么，但是你得到错误，因为onBackPressed（）不是超类的方法（在你的情况下是Fragment类）

Answer 6

如果您想返回上一个片段，可以使用它。 content_frame是您的FrameLayout的ID。您不能使用onBackPressed，因为如果没有Activity，该片段将无法独立存在。

FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
                        ft.replace(R.id.content_frame, new MainActivity());
                        ft.addToBackStack(null);
                        ft.commit();

onBackPressed（）和Fragments

6 个答案: