Android - fragment 中的 ListView 不显示

Question

这是我的代码有问题。进入事件后，我试图在 ListView 中更新我的 sqlite 数据库数据，但是 ListView 没有显示，而且我不擅长使用 fragment ，任何人都可以指导我我在这里做错了什么？抱歉，我是 Android 应用程序开发的新手。谢谢。

public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.event, container, false);
    show = (Button)rootView.findViewById(R.id.button1);
    show.setOnClickListener(this);
    return rootView;
}

public void onActivityCreated(int requestCode, int resultCode, Intent data) {
    ArrayList<HashMap<String, String>> eventList = controller
            .getAllEvents();
    if (eventList.size() != 0) {
        ListView lv = (ListView) rootView.findViewById(R.id.list);
        lv.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                eventId = (TextView) view.findViewById(R.id.eventId);
                String valEventId = eventId.getText().toString();
                Intent objIndent = new Intent(getActivity(),
                        EditEvent.class);
                objIndent.putExtra("eventId", valEventId);
                startActivity(objIndent);
            }
        });
        ListAdapter adapter = new SimpleAdapter(getActivity(), eventList,
                R.layout.view_event_entry, new String[] { "eventId",
                        "eventName" }, new int[] { R.id.eventId,
                        R.id.eventName });
        lv.setAdapter(adapter);
    }

}

@Override
public void onClick(View v) {
    // TODO Auto-generated method stub
    Intent objIntent = new Intent(getActivity(), AddEvent.class);
    startActivity(objIntent);
}

这是我的 xml 代码:

<RelativeLayout
    android:id="@+id/relativeLayout1"
    android:layout_width="fill_parent"
    android:layout_height="40dp"
    android:orientation="vertical" >

    <Button
        android:id="@+id/button1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@drawable/addevents"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true" />

</RelativeLayout>
<RelativeLayout
    android:id="@id/relativeLayout1"
    android:layout_width="fill_parent"
    android:layout_height="match_parent"
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/relativeLayout1"
    android:orientation="vertical"
    android:layout_marginTop="40dp">

<ListView
     android:id="@+id/list"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:layout_alignParentLeft="true">
 </ListView>
 </RelativeLayout>
</RelativeLayout>

这是设置我的数据库的代码。我想知道这是否是问题发生的地方。大家可以在这里看看。

public EventController(Context applicationcontext) {
    super(applicationcontext, "androidsqlite.db", null, 1);
    Log.d(LOGCAT,"Created");
}

@Override
//create table for the database
public void onCreate(SQLiteDatabase database) {
    String query;
    query = "CREATE TABLE events ( eventId INTEGER PRIMARY KEY, eventName TEXT)";
    database.execSQL(query);    
    Log.d(LOGCAT,"events Created");
}

@Override
//drop the database and reset if required
public void onUpgrade(SQLiteDatabase database, int version_old, int current_version) {
    String query;
    query = "DROP TABLE IF EXISTS events";
    database.execSQL(query);
    onCreate(database);
}

public void insertEvent(HashMap<String, String> queryValues) {
    SQLiteDatabase database = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put("eventName", queryValues.get("eventName"));
    database.insert("events", null, values);
    database.close();
}

public int updateEvent(HashMap<String, String> queryValues) {
    SQLiteDatabase database = this.getWritableDatabase();    
    ContentValues values = new ContentValues();
    values.put("eventName", queryValues.get("eventName"));
    return database.update("events", values, "eventId" + " = ?", new String[] { queryValues.get("eventId") });
    //String updateQuery = "Update  words set txtWord='"+word+"' where txtWord='"+ oldWord +"'";
    //Log.d(LOGCAT,updateQuery);
    //database.rawQuery(updateQuery, null);
    //return database.update("words", values, "txtWord  = ?", new String[] { word });
}

public void deleteEvent(String id) {
    Log.d(LOGCAT,"delete");
    SQLiteDatabase database = this.getWritableDatabase();    
    String deleteQuery = "DELETE FROM  events where eventId='"+ id +"'";
    Log.d("query",deleteQuery);     
    database.execSQL(deleteQuery);
}

public ArrayList<HashMap<String, String>> getAllEvents() {
    ArrayList<HashMap<String, String>> wordList;
    wordList = new ArrayList<HashMap<String, String>>();
    String selectQuery = "SELECT  * FROM events";
    SQLiteDatabase database = this.getWritableDatabase();
    Cursor cursor = database.rawQuery(selectQuery, null);
    if (cursor.moveToFirst()) {
        do {
            HashMap<String, String> map = new HashMap<String, String>();
            map.put("eventId", cursor.getString(0));
            map.put("eventName", cursor.getString(1));
            wordList.add(map);
        } while (cursor.moveToNext());
    }

    // return contact list
    return wordList;
}

public HashMap<String, String> getEventInfo(String id) {
    HashMap<String, String> wordList = new HashMap<String, String>();
    SQLiteDatabase database = this.getReadableDatabase();
    String selectQuery = "SELECT * FROM events where eventId='"+id+"'";
    Cursor cursor = database.rawQuery(selectQuery, null);
    if (cursor.moveToFirst()) {
        do {
                //HashMap<String, String> map = new HashMap<String, String>();
            wordList.put("eventName", cursor.getString(1));
               //wordList.add(map);
        } while (cursor.moveToNext());
    }                   
return wordList;
}   

这是我得到的错误:

10-26 08:02:29.141: E/AndroidRuntime(22646): FATAL EXCEPTION: main 10-26 08:02:29.141: E/AndroidRuntime(22646): java.lang.NullPointerException 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164) 10-26 08:02:29.141: E/AndroidRuntime(22646): at com.example.hapshare.EventController.getAllEvents(EventController.java:70) 10-26 08:02:29.141: E/AndroidRuntime(22646): at com.example.hapshare.Event.onCreateView(Event.java:42) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.app.Fragment.performCreateView(Fragment.java:1478) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.view.ViewPager.populate(ViewPager.java:1068) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.view.ViewPager.populate(ViewPager.java:914) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.View.measure(View.java:15696) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4851) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.View.measure(View.java:15696) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.widget.LinearLayout.measureVertical(LinearLayout.java:847) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.widget.LinearLayout.onMeasure(LinearLayout.java:588) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.View.measure(View.java:15696) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4851) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 10-26 08:02:29.141: E/AndroidRuntime(22646): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2261) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.View.measure(View.java:15696) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2221) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1287) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1524) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1187) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4855) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:766) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.Choreographer.doCallbacks(Choreographer.java:575) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.Choreographer.doFrame(Choreographer.java:542) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:751) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.os.Handler.handleCallback(Handler.java:725) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.os.Handler.dispatchMessage(Handler.java:92) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.os.Looper.loop(Looper.java:158) 10-26 08:02:29.141: E/AndroidRuntime(22646): at android.app.ActivityThread.main(ActivityThread.java:5777) 10-26 08:02:29.141: E/AndroidRuntime(22646): at java.lang.reflect.Method.invokeNative(Native Method) 10-26 08:02:29.141: E/AndroidRuntime(22646): at java.lang.reflect.Method.invoke(Method.java:511) 10-26 08:02:29.141: E/AndroidRuntime(22646): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1083) 10-26 08:02:29.141: E/AndroidRuntime(22646): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:850) 10-26 08:02:29.141: E/AndroidRuntime(22646): at dalvik.system.NativeStart.main(Native Method)

Answer 1

您的代码中有几处会引发危险信号。这引出了我的第一个问题:您使用的是 eclipse 还是 intellij？因为它看起来甚至不会编译给我。也许你在这里编辑了这个，但现在帮助你让它工作。甚至不要使用 onActivityCreated 在 Fragment 中初始化你的 ListView(Andrew 也正确地指出你甚至没有正确使用它，这就是我的原因惊讶它甚至编译，如果它是)。您应该在 onCreateView 中执行此操作。现在我将发布我编辑过的代码。我没有对其进行测试，因此它可以更好地指导它应该是什么样子(并希望它可以编译)。

  public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.event, container, false);

    ArrayList<HashMap<String, String>> eventList = controller
            .getAllEvents();
    if (eventList.size() != 0) {
        ListView lv = (ListView) rootView.findViewById(R.id.list);
        lv.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                eventId = (TextView) view.findViewById(R.id.eventId);
                String valEventId = eventId.getText().toString();
                Intent objIndent = new Intent(getActivity(),
                        EditEvent.class);
                objIndent.putExtra("eventId", valEventId);
                startActivity(objIndent);
            }
        });
        ListAdapter adapter = new SimpleAdapter(getActivity(), eventList,
                R.layout.view_event_entry, new String[] { "eventId",
                        "eventName" }, new int[] { R.id.eventId,
                        R.id.eventName });
        lv.setAdapter(adapter);
    }
    show = (Button)rootView.findViewById(R.id.button1);
    show.setOnClickListener(this);

    return rootView;
}
...