onBackPressed() 和片段

Question

我正在尝试在我的 Fragment 中使用 onBackPressed()，这样我就可以允许用户在他在我的应用程序中导航的一堆片段中回滚。

问题是，当我将下面的方法添加到我的 Fragment 时，它给我错误：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

在 Activity class 中使用方法 onBackPressed() 并调用 popBackStack()，而不是在片段

中

Answer 2

如果我误解了或者遗漏了什么，我很抱歉，但是你会收到错误消息，因为 onBackPressed() 不是 super class 的方法（在你的情况下是片段 class）

Answer 3

问题是 Fragment 没有 public void onBackPressed() 方法。

你收到错误是因为你的方法用 @Override 注释，但它实际上并没有覆盖超类中的任何方法。 @Override 的目的正是这个，让你知道你认为你正在压倒某些东西，但实际上你没有

附带说明一下，您尝试做的事情是不必要的。如果你按下后退按钮并且你在后退堆栈中有片段，它们将被自动弹出。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 4

为了达到你想要的效果，你应该像这样覆盖 Activity 关联的 onBackPressed()：

@Override
public void onBackPressed() {
    if (getSupportFragmentManager().getBackStackEntryCount() > 1) {
        getSupportFragmentManager().popBackStack();
    } else {
      finish();
    }
}

希望这对您有所帮助。对不起我的英语。

Answer 5

如果你想回到之前的片段，你可以使用这个。 content_frame 是您的 FrameLayout 的 ID。您不能使用 onBackPressed，因为没有 Activity.

片段就无法独立存在

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

Answer 6

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();
        }
    }
});

onBackPressed() 和片段

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