如何实现OnFragmentInteractionListener

Question

我在android studio 0.8.2中有一个带导航抽屉的向导生成应用程序

我创建了一个片段并使用newInstance()添加它,我收到此错误:

com.domain.myapp E/AndroidRuntime:FATAL EXCEPTION:main java.lang.ClassCastException:com.domain.myapp.MainActivity@422fb8f0必须实现OnFragmentInteractionListener

我找不到任何地方如何实现这个OnFragmentInteractionListener？即使在android sdk文档中也找不到它!

MainActivity.java

import android.app.Activity;

import android.app.ActionBar;
import android.app.Fragment;
import android.app.FragmentManager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;


public class MainActivity extends Activity
    implements NavigationDrawerFragment.NavigationDrawerCallbacks {

/**
 * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
 */
private NavigationDrawerFragment mNavigationDrawerFragment;

/**
 * Used to store the last screen title. For use in {@link #restoreActionBar()}.
 */
private CharSequence mTitle;

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

    mNavigationDrawerFragment = (NavigationDrawerFragment)
            getFragmentManager().findFragmentById(R.id.navigation_drawer);
    mTitle = getTitle();

    // Set up the drawer.
    mNavigationDrawerFragment.setUp(
            R.id.navigation_drawer,
            (DrawerLayout) findViewById(R.id.drawer_layout));
}

@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    FragmentManager fragmentManager = getFragmentManager();

    switch (position) {
        case 0: fragmentManager.beginTransaction()
                .replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
                .commit(); break; 
        case 1: fragmentManager.beginTransaction() 
                .replace(R.id.container, AboutFragment.newInstance("test1", "test2"))
                .commit(); break; // this crashes the app
        case 2: fragmentManager.beginTransaction()
                .replace(R.id.container, BrowseQuotesFragment.newInstance("test1", "test2"))
                .commit(); break; // this crashes the app
    }
}


public void onSectionAttached(int number) {
    switch (number) {
        case 1:
            mTitle = getString(R.string.title_section1);
            break;
        case 2:
            mTitle = getString(R.string.title_section2);
            break;
        case 3:
            mTitle = getString(R.string.title_section3);
            break;
    }
}

public void restoreActionBar() {
    ActionBar actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
    actionBar.setDisplayShowTitleEnabled(true);
    actionBar.setTitle(mTitle);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    if (!mNavigationDrawerFragment.isDrawerOpen()) {
        // Only show items in the action bar relevant to this screen
        // if the drawer is not showing. Otherwise, let the drawer
        // decide what to show in the action bar.
        getMenuInflater().inflate(R.menu.main, menu);
        restoreActionBar();
        return true;
    }
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    private static final String ARG_SECTION_NUMBER = "section_number";

    /**
     * Returns a new instance of this fragment for the given section
     * number.
     */
    public static PlaceholderFragment newInstance(int sectionNumber) {
        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    public PlaceholderFragment() {
    }

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

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((MainActivity) activity).onSectionAttached(
                getArguments().getInt(ARG_SECTION_NUMBER));
    }
}

}

Answer 1

对于那些在阅读@meda答案后仍然不理解的人,这里是我对这个问题的简明扼要的完整解释:

比方说,你有2个片段,Fragment_A以及Fragment_B它们是自动生成的,从应用程序.在生成的片段的底部,您将找到此代码:

public class Fragment_A extends Fragment {

    //rest of the code is omitted

    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        public void onFragmentInteraction(Uri uri);
    }
}

public class Fragment_B extends Fragment {

    //rest of the code is omitted

    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        public void onFragmentInteraction(Uri uri);
    }
}

要解决此问题,您必须在onFragmentInteraction您的活动中添加方法,在我的案例中,该方法已命名MainActivity2.之后,您需要实现如下所示的所有片段implements:

public class MainActivity2 extends ActionBarActivity
        implements Fragment_A.OnFragmentInteractionListener, 
                   Fragment_B.OnFragmentInteractionListener, 
                   NavigationDrawerFragment.NavigationDrawerCallbacks {
    //rest code is omitted

    @Override
    public void onFragmentInteraction(Uri uri){
        //you can leave it empty
    }
}

PS:简而言之,这种方法可用于片段之间的通信.对于那些想要了解更多有关此方法的人,请参阅此链接.

Answer 2

这里发布的答案没有帮助,但以下链接做了:

http://developer.android.com/training/basics/fragments/communicating.html

定义接口

public class HeadlinesFragment extends ListFragment {
    OnHeadlineSelectedListener mCallback;

    // Container Activity must implement this interface
    public interface OnHeadlineSelectedListener {
        public void onArticleSelected(int position);
    }

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

        // This makes sure that the container activity has implemented
        // the callback interface. If not, it throws an exception
        try {
            mCallback = (OnHeadlineSelectedListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement OnHeadlineSelectedListener");
        }
    }

    ...
}

例如,当用户单击列表项时,将调用片段中的以下方法.该片段使用回调接口将事件传递给父活动.

@Override
public void onListItemClick(ListView l, View v, int position, long id) {
    // Send the event to the host activity
    mCallback.onArticleSelected(position);
}

实现接口

例如,以下活动实现了上面示例中的接口.

public static class MainActivity extends Activity
        implements HeadlinesFragment.OnHeadlineSelectedListener{
    ...

    public void onArticleSelected(int position) {
        // The user selected the headline of an article from the HeadlinesFragment
        // Do something here to display that article
    }
}

API 23更新:2015年8月31日

onAttach(Activity activity)现在不推荐使用覆盖方法android.app.Fragment,代码应该升级到onAttach(Context context)

@Override
public void onAttach(Context context) {
    super.onAttach(context);
}


@Override
public void onStart() {
    super.onStart();
    try {
        mListener = (OnFragmentInteractionListener) getActivity();
    } catch (ClassCastException e) {
        throw new ClassCastException(getActivity().toString()
                + " must implement OnFragmentInteractionListener");
    }
}

Answer 3

查看FragmentAndroid Studio 自动生成的内容.当您创建新的时Fragment,Studio会为您存储一堆代码.在自动生成的模板的底部,有一个名为的内部接口定义OnFragmentInteractionListener.您Activity需要实现此接口.这是您Fragment通知Activity事件的推荐模式,以便它可以采取适当的操作,例如加载另一个Fragment.有关详细信息,请参阅此页面,查找"为活动创建事件回调"部分:http://developer.android.com/guide/components/fragments.html

Answer 4

对于那些访问此页面寻找有关此错误的进一步说明的人,在我的情况下,调用片段的活动需要在这种情况下有2个实现,如下所示:

public class MyActivity extends Activity implements 
    MyFragment.OnFragmentInteractionListener, 
    NavigationDrawerFragment.NaviationDrawerCallbacks {
    ...// rest of the code
}

Answer 5

您应该尝试从片段中删除以下代码

    try {
        mListener = (OnFragmentInteractionListener) activity;
    } catch (ClassCastException e) {
        throw new ClassCastException(activity.toString()
                + " must implement OnFragmentInteractionListener");
    }

接口/侦听器是默认创建的,以便您的活动和片段可以更轻松地进行通信

Answer 6

对我来说，它可以删除此代码：

@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");
        }
    }

结局是这样的：

@Override
public void onAttach(Context context) {
    super.onAttach(context);
}

Answer 7

除了@ user26409021的答案之外，如果您添加了ItemFragment，则ItemFragment中的消息是：

Activities containing this fragment MUST implement the {@link OnListFragmentInteractionListener} interface.

并且您应该添加您的活动；

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener, ItemFragment.OnListFragmentInteractionListener {

//the code is omitted

 public void onListFragmentInteraction(DummyContent.DummyItem uri){
    //you can leave it empty
}

这里的虚拟物品是您在ItemFragment底部的物品