字段插槽，SQLite的不良要求 - Android

Question

我有一個表中有6列，我試圖從只有3列獲取所有行，並將其存儲在數組中以使用它。我的查詢是這樣的：

public Cursor fetchInfo(long rowId) throws SQLException 
    { 
     Cursor mCursor = mDb.query(true, DATABASE_TABLE, new String[] {"_id", "xCoord", "yCoord", "color"}, "_id" + "=" + rowId, null, null, null, null, null); 

     if(mCursor != null) 
     { 
      mCursor.moveToFirst(); 
     } 
     return mCursor; 
    } 

然後我打電話給它，如下所示：

private void getInfo() 
    { 
     Cursor mCursor = mDbHelper.fetchInfo(mRowId); 
     x = new float[mCursor.getCount()]; 
     y = new float[mCursor.getCount()]; 
     color = new int[mCursor.getCount()]; 

     if(mCursor.moveToFirst()) 
     { 
      for(int i = 0; i < mCursor.getCount(); i++) 
      { 
       x[i] = mCursor.getFloat(3); 
       y[i] = mCursor.getFloat(4); //Line 76, this is where the error is occurs. 
       color[i] = mCursor.getInt(5); 
      } 
     } 
     mCursor.close(); 
    } 

然而，當我嘗試運行此，我得到一個錯誤說：

12-19 15:40:36.903: E/CursorWindow(276): Bad request for field slot 0,4. numRows = 1, numColumns = 4 
12-19 15:40:36.903: D/AndroidRuntime(276): Shutting down VM 
12-19 15:40:36.912: W/dalvikvm(276): threadid=1: thread exiting with uncaught exception (group=0x4001d800) 
12-19 15:40:36.922: E/AndroidRuntime(276): FATAL EXCEPTION: main 
12-19 15:40:36.922: E/AndroidRuntime(276): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.x17.projects.strikezone/com.x17.projects.strikezone.SavedEntries}: java.lang.IllegalStateException: get field slot from row 0 col 4 failed 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.os.Handler.dispatchMessage(Handler.java:99) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.os.Looper.loop(Looper.java:123) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.app.ActivityThread.main(ActivityThread.java:4627) 
12-19 15:40:36.922: E/AndroidRuntime(276): at java.lang.reflect.Method.invokeNative(Native Method) 
12-19 15:40:36.922: E/AndroidRuntime(276): at java.lang.reflect.Method.invoke(Method.java:521) 
12-19 15:40:36.922: E/AndroidRuntime(276): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
12-19 15:40:36.922: E/AndroidRuntime(276): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
12-19 15:40:36.922: E/AndroidRuntime(276): at dalvik.system.NativeStart.main(Native Method) 
12-19 15:40:36.922: E/AndroidRuntime(276): Caused by: java.lang.IllegalStateException: get field slot from row 0 col 4 failed 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.database.CursorWindow.getDouble_native(Native Method) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.database.CursorWindow.getFloat(CursorWindow.java:451) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.database.AbstractWindowedCursor.getFloat(AbstractWindowedCursor.java:123) 
12-19 15:40:36.922: E/AndroidRuntime(276): at com.x17.projects.strikezone.SavedEntries.getInfo(SavedEntries.java:76) 
12-19 15:40:36.922: E/AndroidRuntime(276): at com.x17.projects.strikezone.SavedEntries.onCreate(SavedEntries.java:46) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
12-19 15:40:36.922: E/AndroidRuntime(276): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 
12-19 15:40:36.922: E/AndroidRuntime(276): ... 11 more 

我是新來的數據庫，所以我不知道如何解決這個問題。我嘗試了一些不同的方法來解決這個問題，但沒有成功。我在這裏做錯了什麼？我應該這樣做嗎？

Answer 1

在fetchInfo()方法內的查詢中，您從DB Table獲得4列。

作爲文檔指出getFloat(int index)這種方法預計爲指標：

索引 - 目標列的基於零的索引。

所以，你應該如下使用索引：

0 - 爲_id

1 - 爲xCoord

2 - 爲yCoord

3 - 爲color