java - 接口(interface) java/Android 不能从子 fragment 到父 fragment

Question

我试图在两个 fragment 中进行交流，主要 fragment 和子 fragment 。但是，当我在子 fragment 中声明接口(interface)以将值传递给主 fragment 时，它工作正常，但是当我想从主 fragment 传递给子 fragment 时，它不起作用。顺便说一句， fragment 在我的 MainActivity 中。感谢您的帮助。

错误信息是:

Caused by: java.lang.IllegalArgumentException: com.example.example.example.MainActivity must implement interface NotifyOnTutorialPageSelected

那么有没有办法不用直接使用静态函数就可以传值呢？因为我注意到只有父级才能实现接口(interface)，所以如果我想用接口(interface)实现它该怎么办？顺便说一句，它是为了学习目的。

代码:

//MAin activity is something that calls only the mainfragment
public class MainActivity extends ActionBarActivity {

    FragmentManager fragmentManager;
    TutorialFragment tutorialFragment;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ActionBar actionBar = getSupportActionBar();
        actionBar.hide();


        fragmentManager = getSupportFragmentManager();    
        fragmentManager.findFragmentById(R.id.card_message_frag);
        tutorialFragment = (TutorialFragment) fragmentManager.findFragmentById(R.id.tutorial_frag);

    }
}

FIRST CLASS(由 MainActivity 调用)

public class TutorialFragment extends Fragment implements ViewPager.OnPageChangeListener, OnTabSelected {

    FragmentManager fragmentManager;
    MultiTabFragment multiTabFragment;
    NotifyOnTutorialPageSelected notifyOnTutorialPageSelected;
    View tab ;
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        final View view = inflater.inflate(R.layout.fragment_tutorial, container, false);
        fragmentManager = getChildFragmentManager();
        multiTabFragment = (MultiTabFragment) fragmentManager.findFragmentById(R.id.multi_tabs_frag);
        tab.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        //Log.e("clicked tab# ", "" + tabIndex);
                        onTabSelected.onTabSelected(tabIndex);
                    }
                });
        return view;
    }

    @Override
    public void onPageSelected(int position) {  
        notifyOnTutorialPageSelected.notifyOnTutorialPageSelected(position); // do something so can communicate with the child fragment
    }


    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        if (getActivity() instanceof NotifyOnTutorialPageSelected) {
            notifyOnTutorialPageSelected = (NotifyOnTutorialPageSelected) getActivity();
        } else if (getParentFragment() instanceof OnTabSelected) {
            notifyOnTutorialPageSelected = (NotifyOnTutorialPageSelected) getParentFragment();
        } else {
            throw new IllegalArgumentException(activity + " must implement interface " + NotifyOnTutorialPageSelected.class.getSimpleName());
        }

    }

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

    @Override
    public void onTabSelected(int index) {
        Log.e("INDEX_PASSED", "" + index);
        pager.setCurrentItem(index);
    }
}

SECOND CLASS(由 TutorialFragment 调用)

public class MultiTabFragment extends Fragment implements NotifyOnTutorialPageSelected{
    private OnTabSelected onTabSelected;

    final int totalTabs = 4;

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


    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        if (getActivity() instanceof OnTabSelected) {
            onTabSelected = (OnTabSelected) getActivity();
        } else if (getParentFragment() instanceof OnTabSelected) {
            onTabSelected = (OnTabSelected) getParentFragment();
        } else {
            throw new IllegalArgumentException(activity + " must implement interface " + OnTabSelected.class.getSimpleName());
        }
    }

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

    @Override
    public void notifyOnTutorialPageSelected(int index) {
        deselectPreviousTab(index);
    }

解决方案:

由于没有人回答这个问题，如果有人有类似的困难，我会把答案留在这里。我通过实现 MainActivity 的接口(interface)解决了这个问题，这样主 Activity 将调用子类并调用方法:

//MAin activity is something that calls only the mainfragment
public class MainActivity extends ActionBarActivity implements NotifyOnTutorialPageSelected{

    FragmentManager fragmentManager;
    TutorialFragment tutorialFragment;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ActionBar actionBar = getSupportActionBar();
        actionBar.hide();


        fragmentManager = getSupportFragmentManager();    
        fragmentManager.findFragmentById(R.id.card_message_frag);
        tutorialFragment = (TutorialFragment) fragmentManager.findFragmentById(R.id.tutorial_frag);

    }

@Override
    public void notifyOnTutorialPageSelected(int index) {
        FragmentManager fragmentChildManager = tutorialFragment.getChildFragmentManager();
        MultiTabFragment multiTabFragment = (MultiTabFragment) fragmentChildManager.findFragmentById(R.id.multi_tabs_frag);
        multiTabFragment.deselectPreviousTab(index);
    }
}

它对我有用，或者至少对我想要的有用，如果有人有不同的解决方案，请告诉我，谢谢。

Answer 1

您自己抛出了异常，因为您的 Activity 未实现 NotifyOnTutorialPageSelected 接口(interface)，并且您的父 fragment 不得实现 OnTabSelected 接口(interface)。

以下代码需要固定为前两个条件之一为真。顺便说一句，你的 else if 语句中有一个潜在的错误，因为你只是检查它是否是 instanceOf OnTabSelected 但随后将父 fragment 转换为 NotifyOnTutorialPageSelected :

@Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        if (getActivity() instanceof NotifyOnTutorialPageSelected) {
            notifyOnTutorialPageSelected = (NotifyOnTutorialPageSelected) getActivity();
        } else if (getParentFragment() instanceof OnTabSelected) {
            notifyOnTutorialPageSelected = (NotifyOnTutorialPageSelected) getParentFragment();
        } else {
            throw new IllegalArgumentException(activity + " must implement interface " + NotifyOnTutorialPageSelected.class.getSimpleName());
        }

    }

查看您的代码，我看不出您是如何拥有子 fragment 的，因为您的教程 fragment 并未创建子 fragment 。

您是否尝试让一个 Activity 显示两个相互通信的 fragment ？

如果是，请查看 Android Documentation了解如何使用界面来做到这一点。

编辑:

通过这次学习经历，您可能会发现您的代码存在更多错误。但是为了让您继续前进并远离当前错误，请删除 TutorialFragment fragment 中的 onAttach 方法，因为无论如何它都是错误的。如果您要让您的 Activity 类实现回调接口(interface)，那么它就会去那里。由于您没有那样做，因此检查您的 Activity 是否实现了该特定接口(interface)是没有意义的。

您的 MultiTabFragment.onAttach 方法只需要以下内容，除非您有时要将 fragment 直接放入 Activity 中:

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);

    if (getParentFragment() instanceof OnTabSelected) {
        onTabSelected = (OnTabSelected) getParentFragment();
    } else {
        throw new IllegalArgumentException("Parent Fragment must implement interface " + OnTabSelected.class.getSimpleName());
    }
}

最后，由于您已经在 TutorialFragment 中保留对 MultiTabFragment 的引用，因此请删除 NotifyOnTutorialPageSelected notifyOnTutorialPageSelected; 并直接调用该 fragment 。

@Override
public void onPageSelected(int position) {  
    multiTabFragment.notifyOnTutorialPageSelected(position); // do something so can communicate with the child fragment
}