的Android CursorLoader和LoaderManager错误

Question

我想落实的10

一分钟API一个CursorLoader和LoaderManager不过，我一直在AsyncTaskLoader.class的63号线（在AsyncTaskLoader的源代码得到一个IllegalArgument异常的.class其中例外的情况是下面，并在此link

/* Runs on the UI thread */ 
@Override 
protected void onPostExecute(D data) { 
    if (DEBUG) Log.v(TAG, this + " onPostExecute"); 
    try { 
     AsyncTaskLoader.this.dispatchOnLoadComplete(this, data); 
    } finally { 
     done.countDown(); 
    } 
} 

下面是在错误的堆栈：

AsyncTaskLoader$LoadTask.onPostExecute(Object) line: 63 
AsyncTaskLoader$LoadTask(ModernAsyncTask).finish(Object) line: 461 
ModernAsyncTask.access$500(ModernAsyncTask, Object) line: 47  
ModernAsyncTask$InternalHandler.handleMessage(Message) line: 474  
ModernAsyncTask$InternalHandler(Handler).dispatchMessage(Message) line: 99 
Looper.loop() line: 137 
ActivityThread.main(String[]) line: 4424  
Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method] 
Method.invoke(Object, Object...) line: 511 
ZygoteInit$MethodAndArgsCaller.run() line: 784 
ZygoteInit.main(String[]) line: 551 
NativeStart.main(String[]) line: not available [native method] 

我测试了我的内容提供程序，并验证了查询方法从我的Sqlite数据库返回了有效的光标。下面是我想实现我的CursorLoader活动的源代码和LoaderManager：

import android.database.Cursor; 
import android.os.Bundle; 
import android.support.v4.app.FragmentActivity; 
import android.support.v4.app.LoaderManager; 
import android.support.v4.content.CursorLoader; 
import android.support.v4.content.Loader; 
import android.support.v4.widget.SimpleCursorAdapter; 
import android.widget.ListView; 

public class Screen1_MainData extends FragmentActivity implements LoaderManager.LoaderCallbacks<Cursor> { 

    SimpleCursorAdapter adapter; 
    ListView lv; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.screen1_maindata); 
     initLoader(); 
    } 

    void initLoader() { 
     String[] uiBindFrom = { Useful_Info_TableMetaData.USEFUL_INFO_COLUMN_NAME }; 
     int[] uiBindTo = { R.id.name }; 
     lv = (ListView) findViewById(R.id.screen1_MainListView); 
     getSupportLoaderManager().initLoader(0, null, this); 

     adapter = new SimpleCursorAdapter(this, R.layout.row, null, uiBindFrom, 
       uiBindTo, 0); 
     lv.setAdapter(adapter);  
    } 

@Override 
public Loader<Cursor> onCreateLoader(int arg0, Bundle arg1) { 

    String[] projection = { Useful_Info_TableMetaData.USEFUL_INFO_COLUMN_NAME }; 

    return new CursorLoader(
      this, // The Activity context 
      Useful_Info_TableMetaData.CONTENT_URI, projection, null, null, 
      null); 
} 

    @Override 
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) { 
     adapter.swapCursor(data); 
    } 

    @Override 
    public void onLoaderReset(Loader<Cursor> loader) { 
     adapter.swapCursor(null); 
    } 
} 

没有人在这里看到的东西，我做错了什么？

谢谢。

---

的应用程序似乎使它到

@Override 
public void onLoadFinished(Loader<Cursor> loader, Cursor data) { 
    adapter.swapCursor(data); 
} 

，然后抛出异常出现。

下面是logcat的：

08-03 23:33:20.736: E/AndroidRuntime(17256): FATAL EXCEPTION: main 
08-03 23:33:20.736: E/AndroidRuntime(17256): java.lang.IllegalArgumentException: column '_id' does not exist 
08-03 23:33:20.736: E/AndroidRuntime(17256): at android.database.AbstractCursor.getColumnIndexOrThrow(AbstractCursor.java:267) 
08-03 23:33:20.736: E/AndroidRuntime(17256): at android.database.CursorWrapper.getColumnIndexOrThrow(CursorWrapper.java:78) 
08-03 23:33:20.736: E/AndroidRuntime(17256): at android.support.v4.widget.CursorAdapter.swapCursor(CursorAdapter.java:344) 
08-03 23:33:20.736: E/AndroidRuntime(17256): at android.support.v4.widget.SimpleCursorAdapter.swapCursor(SimpleCursorAdapter.java:326) 

Answer 1

试试您的来电lv.setAdapter后移动initLoader。这将确保 （因此adapter.swapCursor(data)）将被称为已与ListView相关联。

另外，请确保您的数据库有一个名为_id的列作为您的主键，因为CursorAdapter将不起作用。需要返回_id作为CursorLoader的结果的一部分。否则会抛出异常。