更改listfragment内容

Question

我使用listfragment并尝试更改它的内容。这里是我的活动代码：

public class MainActivity extends Activity { 
    public static Context appContext; 
    public ToFragment ToFragment; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState);  
     setContentView(R.layout.activity_main); 
     ActionBar actionbar = getActionBar(); 
     actionbar.setDisplayShowTitleEnabled(false); 
     actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 
     ActionBar.Tab FromTab = actionbar.newTab().setText("FromFragment"); 
     ActionBar.Tab ToTab = actionbar.newTab().setText("ToFragment"); 

     FromFragment FromFragment = new FromFragment(); 
     ToFragment ToFragment = new ToFragment(); 

     ToTab.setTabListener(new MyTabsListener(ToFragment)); 
     FromTab.setTabListener(new MyTabsListener(FromFragment)); 

//  ListView tolistview = ToFragment.getListView(); 
//  ListView fromlistview = FromFragment.getListView(); 

     actionbar.addTab(ToTab); 
     actionbar.addTab(FromTab); 
    } 

     @Override 
     public boolean onCreateOptionsMenu(Menu menu) { 
     MenuInflater inflater = getMenuInflater(); 
     inflater.inflate(R.menu.mainmenu, menu); 
     return true; 
     } 

     @Override 
     public boolean onOptionsItemSelected(MenuItem item) { 
     switch (item.getItemId()) { 
     case R.id.action_refresh: 
      String[] countries = new String[] { 
        "Russia", 
        "USA", 
       }; 
      ToFragment.changeContent(countries); 
      break; 
     case R.id.action_settings: 

      break; 

     default: 
      break; 
     } 

     return true; 
     } 
} 

在这里，我初始化2个listfragments，ToFragment和FromFragment。然后在这里（onCreateOptionsMenu）我尝试通过我的函数changeContent更改ToFragment的内容。这里是片段的代码：我tryed使功能changeContent工作就像函数onCreateView

public class ToFragment extends ListFragment { 
    String[] countries = new String[] { 
      "India", 
      "Pakistan", 
     }; 
    private LayoutInflater inflater; 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     this.inflater = inflater; 
     ArrayAdapter<String> adapter = new ArrayAdapter<String>(inflater.getContext(), android.R.layout.simple_list_item_1, countries); 

     setListAdapter(adapter); 

     return super.onCreateView(inflater, container, savedInstanceState); 
    } 

    public void changeContent(String[] array) { 
     ArrayAdapter<String> adapter = new ArrayAdapter<String>(inflater.getContext(), android.R.layout.simple_list_item_1, array); 
     setListAdapter(adapter); 
    } 

，如你所见。但！我的问题是，它在这里抛出nullpointerexception，我真的很困惑，我不明白什么是问题！你能告诉我什么是错的吗？或者你可以建议更好的方式来改变listfragment内容？

这是错误的轨道：

04-08 22:48:33.292: I/System.out(8817): adapter == null 
04-08 22:48:33.292: W/dalvikvm(8817): threadid=1: thread exiting with uncaught exception (group=0x414572d0) 
04-08 22:48:33.297: E/AndroidRuntime(8817): FATAL EXCEPTION: main 
04-08 22:48:33.297: E/AndroidRuntime(8817): java.lang.RuntimeException: Unable to start activity ComponentInfo{ru.rkarasev.miptrain/ru.rkarasev.miptrain.MainActivity}: java.lang.NullPointerException 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2355) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.app.ActivityThread.access$600(ActivityThread.java:151) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1335) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.os.Handler.dispatchMessage(Handler.java:99) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.os.Looper.loop(Looper.java:155) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.app.ActivityThread.main(ActivityThread.java:5493) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at java.lang.reflect.Method.invokeNative(Native Method) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at java.lang.reflect.Method.invoke(Method.java:511) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:795) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at dalvik.system.NativeStart.main(Native Method) 
04-08 22:48:33.297: E/AndroidRuntime(8817): Caused by: java.lang.NullPointerException 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at ru.rkarasev.miptrain.ToFragment.changeContent(ToFragment.java:34) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at ru.rkarasev.miptrain.MainActivity.onCreate(MainActivity.java:49) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.app.Activity.performCreate(Activity.java:5066) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1101) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2311) 
04-08 22:48:33.297: E/AndroidRuntime(8817):  ... 11 more 
04-08 22:48:35.382: D/Process(8817): killProcess, pid=8817 
04-08 22:48:35.387: D/Process(8817): dalvik.system.VMStack.getThreadStackTrace(Native Method) 
04-08 22:48:35.387: D/Process(8817): java.lang.Thread.getStackTrace(Thread.java:599) 
04-08 22:48:35.387: D/Process(8817): android.os.Process.killProcess(Process.java:944) 
04-08 22:48:35.392: D/Process(8817): com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException(RuntimeInit.java:108) 
04-08 22:48:35.392: D/Process(8817): java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:693) 
04-08 22:48:35.392: D/Process(8817): java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:690) 
04-08 22:48:35.392: D/Process(8817): dalvik.system.NativeStart.main(Native Method) 

Answer 1

更改你如何创建ArrayAdapter实例：

ArrayList<String> arrayList = new ArrayList<String>(); 
arrayList.addAll(Arrays.asList(countries)); 

ArrayAdapter<String> adapter = new ArrayAdapter<String>(inflater.getContext(), android.R.layout.simple_list_item_1, arrayList); 

正如这个答案发现：Unable to modify ArrayAdapter in ListView: UnsupportedOperationException

public void changeContent(String[] array) { 
    ArrayAdapter<String> adapter = (ArrayAdapter<String>)getListAdapter(); 
    if (adapter != null) { 
     adapter.clear(); 
     adapter.addAll(Arrays.asList(array)); 
     adapter.notifyDataSetChanged(); 
    } 
} 

你不需要每次重新创建适配器。只需清除并设置新阵列，然后通知适配器数据集已更改，以便更新视图。