java - 方向改变时处理多个 fragment

Question

我有一个 MainActivity，我想将一个包含 3 个按钮的 fragment 附加到该 Activity 。单击按钮 1 时，它应将此 fragment 替换为另一个 fragment 。但是当我改变方向时，当前 fragment 和旧 fragment 都被附加了。有人可以帮我解决这个问题吗？

以下是我的MainActivity.java:

public class MainActivity extends AppCompatActivity implements OnButtonsClickListener {

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


        getSupportFragmentManager().beginTransaction()
                .add(R.id.mainactivity, new FragmentHomepage(), "aboutMe")
                .commit();

    }




    @Override
    public void button1Action() {
        FragmentAboutMe fragmentAboutMe=new FragmentAboutMe();
        getSupportFragmentManager().beginTransaction()
                .add(R.id.mainactivity,fragmentAboutMe)
                .commit();
    }

    @Override
    public void button2Action() {
        Intent intent =new Intent(this,ActivityMasterDetail.class);
        startActivity(intent);
    }

    @Override
    public void button3Action() {
        Intent intent =new Intent(this,ActivityViewPager.class);
        startActivity(intent);
    }
}

这是我的FragmentHomepage.java:

public  class FragmentHomepage extends Fragment {
    private static final String ARG_SECTION_NUMBER ="section number";
    OnButtonsClickListener onButtonsClickListener;
    public static FragmentHomepage newInstance(int sectionNumber){
        FragmentHomepage fragmentHomepage=new FragmentHomepage();
        Bundle args=new Bundle();
        args.putInt(ARG_SECTION_NUMBER,sectionNumber);
        fragmentHomepage.setArguments(args);
        return fragmentHomepage;
    }
    public FragmentHomepage(){}

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        try {
            onButtonsClickListener= (OnButtonsClickListener) context;
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        final Button button1= (Button) getActivity().findViewById(R.id.aboutMe);
        final Button button2= (Button) getActivity().findViewById(R.id.task2);
        final Button button3= (Button) getActivity().findViewById(R.id.task3);
        button1.setOnClickListener(new Button.OnClickListener() {
            @Override
            public void onClick(View v) {
                onButtonsClickListener.button1Action();
            }
        });
        button2.setOnClickListener(new Button.OnClickListener() {
            @Override
            public void onClick(View v) {
                onButtonsClickListener.button2Action();
            }
        });
        button3.setOnClickListener(new Button.OnClickListener() {
            @Override
            public void onClick(View v) {
                onButtonsClickListener.button3Action();
            }
        });

    }

    @Nullable
    @Override
    public View onCreateView(final LayoutInflater inflater,
                             ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView=null;
        rootView =inflater.inflate(R.layout.fragment_homepage,container,false);
        return rootView;
    }
}

我的第二个 Activity 如下(在 FragmentAboutMe.java 中):

public class FragmentAboutMe extends Fragment {
    int counters=0;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if(savedInstanceState==null)counters=0;
        else counters=savedInstanceState.getInt("count");

    }

    @Override

    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putInt("count",13);

    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater,
                             ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_aboutme,container,false);
    }
}

Answer 1

在您的 onCreate() 方法中检查 fragment 是否已经存在。 Android 会在方向更改时自动恢复 fragment 管理器状态，因此在方向更改时，您在单击按钮时添加的 fragment 将自动添加。因此，如果您未经检查就在 onCreate() 中添加新 fragment ，这将导致添加 2 个 fragment 。这是导致问题的原因。

FragmentManager fm = getSupportFragmentManager();

if (fm.findfragmentById(R.id.mainactivity) == null) {
     FragmentHomepage fragment = new FragmentHomepage ();
     fm.beginTransaction().add (R.id.mainactivity, fragment).commit();
}