java - viewpager 中的 fragment 转换问题

Question

我是 Android 开发新手。在我的应用程序中有两个选项卡(我使用 view pager 来开发此选项卡)，每个选项卡都包含列表(FragmentA 和 FragmentC)(我使用 listfragment)。当按下/单击两个选项卡中的每个列表项时，它会导航到新 fragment (FragmentB)并显示单击的 ListView 项的所有内容。

我使用了 Communicator 接口(interface)来传达 fragment 和主要 Activity 。第一个 fragment 将数据传递给主 Activity ，然后 Activity 将数据传递给第二个 fragment 。

我的问题:第一个 fragment (FragmentA-listfragment)将数据传递给主要 Activity 。但是当主要 Activity 尝试将数据传递给第二个 fragment (FragmentB)时，它会给出错误。 FragmentA 无法转换为 FragmentB。我花了几天时间试图找到解决方案。但我无法找到合适的解决方案。

通讯器接口(interface)

public interface Communicator {
    void sendData(String msg);
}

FragmentA.java

package com.example.tab;
import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;

/**
 * A simple {@link Fragment} subclass.
 * 
 */
public class FragmentA extends Fragment implements OnItemClickListener {

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

    ListView listView;
    Communicator com;
    View view;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        view = inflater.inflate(R.layout.fragment_a, container, false);
        listView = (ListView) view.findViewById(R.id.listView1);
        ArrayAdapter adapter = ArrayAdapter.createFromResource(getActivity(),
                R.array.books, android.R.layout.simple_list_item_1);
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(this);
        return view;
    }


    @Override
    public void onAttach(Activity activity) {
        // TODO Auto-generated method stub
        super.onAttach(activity);
        com = (Communicator) getActivity();
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
            long id) {

        com.sendData("Hello");

    }

}

FragmentB.java

package com.example.tab;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;

/**
 * A simple {@link Fragment} subclass.
 * 
 */
public class FragmentB extends Fragment {

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

    TextView textView;
    Context context;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        context = getActivity().getBaseContext();
        // Inflate the layout for this fragment
        View view= inflater.inflate(R.layout.fragment_b, container, false);
        textView=   (TextView) view.findViewById(R.id.text1);
        return view;
    }

    public void setData(String msg) {
        Toast.makeText(context, msg, Toast.LENGTH_LONG).show();
        textView.setText(msg);
    }

}

MainActivity.java

package com.example.tab;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.support.v7.app.ActionBarActivity;
import android.app.ActionBar.Tab;
import android.app.ActionBar.TabListener;
import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends ActionBarActivity implements TabListener,
        Communicator {

    ViewPager viewPager;
    ActionBar actionBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewPager = (ViewPager) findViewById(R.id.pager);
        viewPager.setAdapter(new MyAdapter(getSupportFragmentManager()));
        viewPager.setOnPageChangeListener(new OnPageChangeListener() {

            public void onPageSelected(int arg0) {
                // TODO Auto-generated method stub
                actionBar.setSelectedNavigationItem(arg0);
            }

            public void onPageScrolled(int arg0, float arg1, int arg2) {
                // TODO Auto-generated method stub

            }

            public void onPageScrollStateChanged(int arg0) {
                // TODO Auto-generated method stub

            }
        });
        actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        actionBar.setTitle("");

        ActionBar.Tab tab1 = actionBar.newTab().setText("1-50")
                .setTabListener(this);
        ActionBar.Tab tab2 = actionBar.newTab().setText("50-100")
                .setTabListener(this);

        actionBar.addTab(tab1);
        actionBar.addTab(tab2);
        actionBar.setBackgroundDrawable(new ColorDrawable(0xff7e3e00));
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @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);
    }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        // TODO Auto-generated method stub
        viewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        // TODO Auto-generated method stub

    }

    @Override
    public void sendData(String msg) {
        // TODO Auto-generated method stub

        try {
            FragmentManager manager = getSupportFragmentManager();
            FragmentB fragmentB = (FragmentB) manager
                    .findFragmentById(R.id.pager);
            fragmentB.setData(msg);
        } catch (Exception e) {
            // TODO Auto-generated catch block
        }
    }
}

class MyAdapter extends FragmentPagerAdapter {

    public MyAdapter(FragmentManager fm) {
        super(fm);

    }

    @Override
    public Fragment getItem(int arg0) {
        Fragment fragment = null;

        // TODO Auto-generated method stub

        if (arg0 == 0) {
            fragment = new FragmentA();
        }
        if (arg0 == 1) {
            fragment = new FragmentC();
        }
        return fragment;
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return 2;
    }

}

activity_main.xml

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.tab.MainActivity" >

</android.support.v4.view.ViewPager>

错误消息

com.example.tab.FragmentA cannot be cast to com.example.tab.FragmentB

完整的 Logcat:

01-18 13:21:03.380: D/AndroidRuntime(15257): Shutting down VM
01-18 13:21:03.380: W/dalvikvm(15257): threadid=1: thread exiting with uncaught exception (group=0x41572ba8)
01-18 13:21:03.390: E/AndroidRuntime(15257): FATAL EXCEPTION: main
01-18 13:21:03.390: E/AndroidRuntime(15257): Process: com.example.tab, PID: 15257
01-18 13:21:03.390: E/AndroidRuntime(15257): java.lang.ClassCastException: com.example.tab.FragmentA cannot be cast to com.example.tab.FragmentB
01-18 13:21:03.390: E/AndroidRuntime(15257):    at com.example.tab.MainActivity.sendData(MainActivity.java:105)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at com.example.tab.FragmentA.onItemClick(FragmentA.java:52)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at android.widget.AdapterView.performItemClick(AdapterView.java:299)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at android.widget.AbsListView.performItemClick(AbsListView.java:1113)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at android.widget.AbsListView$PerformClick.run(AbsListView.java:2911)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at android.widget.AbsListView$3.run(AbsListView.java:3645)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at android.os.Handler.handleCallback(Handler.java:733)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at android.os.Handler.dispatchMessage(Handler.java:95)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at android.os.Looper.loop(Looper.java:136)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at android.app.ActivityThread.main(ActivityThread.java:5001)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at java.lang.reflect.Method.invokeNative(Native Method)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at java.lang.reflect.Method.invoke(Method.java:515)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
01-18 13:21:03.390: E/AndroidRuntime(15257):    at dalvik.system.NativeStart.main(Native Method)

调试后我可以看到这一行会发生错误

FragmentB fragmentB = (FragmentB) manager.findFragmentById(R.id.pager);

Answer 1

您没有将 FragmentB 附加到 Activity。流程应该是这样的

1.创建一个保存viewpager的fragment(ViewPagerFragment.java)

2.在activity(activity_main.xml)中你应该创建一个FrameLayout

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/content_frame"
    android:layout_width="match_parent"
    android:layout_height="match_parent"></FrameLayout>

3.在 Activity 的 oncreate 方法中添加此代码，将 viewpager Fragment 添加到 Activity

   getSupportFragmentManager().beginTransaction()
            .replace(R.id.content_frame, new ViewPagerFragment())
            .commit();

不要忘记将 viewpager 参数更改为 getChildFragmentManager()

4.从 FragmentA 列表中点击调用此方法，这将用新的 ViewPagerFragment(FragmentB) 替换 ViewPagerFragment

@Override
public void sendData(String msg) {
    try {
        FragmentManager manager = getSupportFragmentManager();
        FragmentTransaction transaction = manager.beginTransaction();
        transaction.replace(R.id.content_frame, new FragmentB().newInstance(msg));
        transaction.addToBackStack(null);
        transaction.commit();

    } catch (Exception e) {
        // TODO Auto-generated catch block
    }
}

将 FragmentB 更改为此。

public class FragmentB extends Fragment {
    private static final String ARG_PARAM1 = "param1";
    String mParam;

    public static FragmentB newInstance(String param1) {
        FragmentB fragment = new FragmentB();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        fragment.setArguments(args);
        return fragment;
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam = getArguments().getString(ARG_PARAM1);
        }
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_b, container, false);
    }
}