从Android数据库中删除项目-游标索引越界异常

Question

在我的android应用程序中，我试图从数据库中删除一个项目，已经在列表视图中选择了相应的项目，并从长按时创建的上下文菜单中选择了一个项目。listview是从arraylist填充的，而arraylist是从数据库中的项创建的。

然而，当我试图删除listview中的第一个项目以外的任何项目时，我会遇到一个错误（这实际上是最近添加的项目，也是arraylist中的最后一个项目，因为listview以相反的顺序显示列表中的项目）。如果我尝试删除一个项目而不是最新的项目，那么我会得到一个错误，android.database.cursorIndexOutOfBoundsException：requested索引0，大小为0。

在这个错误之后，如果我试图打开包含listview的activity，我也会得到同样的错误，直到我删除应用程序的数据并再次打开它。

如果光标是空的并且它正在移动到下一行，我尝试签入databasehandler deleteGoalFromDb方法，但是到目前为止没有成功

在上下文菜单中按下delete项时调用的方法（它是菜单中唯一的项）：

@Override
    public boolean onContextItemSelected(MenuItem item) { //what to do when menu item clicked in context menu
        AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();
        //call delete goal and make it delete goal
        //System.out.println(info.position+"****************");
        int position_actual = goalsList.size() - info.position; //needed as list is displayed in reverse order
        //System.out.println(position_actual+"----------------------");
        deleteGoal(position_actual);
        return true;
    }

我的deleteGoal（）方法：

public void deleteGoal(int id) {
        db.deleteGoalFromDb(id); //deletes the goal from the database
        makeGoalsFromDB(); //refreshes the goalsList
    }

DeleteGoalFromDB：

public void deleteGoalFromDb(int id){
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(TABLE_GOALS, KEY_ID + " = ?", new String[] {id+""});
        db.close();
    }

MakeGoalsFromDB：

public void makeGoalsFromDB() {
        //looping through the table, get the goals and add them to the goals list
        goalsList = new ArrayList<Goal>(); 
        int goalsNo = db.getGoalsCount();
        for (int i = 1; i <= goalsNo; i++) { 
            goalsList.add(db.readGoalFromDb(i));
        }
    }

ReadGoalFromDB：

public Goal readGoalFromDb(int id) { //method to get a goal from the database
        SQLiteDatabase db = this.getWritableDatabase();

        Cursor cursor = db.query(TABLE_GOALS, new String[] { KEY_ID,
                KEY_STROKE, KEY_TIME_HRS, KEY_TIME_MIN, KEY_TIME_SECS, KEY_DISTANCE, KEY_ACHIEVED, KEY_DATE_GOAL }, KEY_ID + "=?",
                new String[] { String.valueOf(id) }, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        Goal goal = new Goal(cursor.getInt(0), cursor.getString(1), cursor.getInt(2),
                cursor.getInt(3), cursor.getInt(4),
                cursor.getInt(5), Boolean.parseBoolean(cursor.getString(6)), cursor.getString(7));

        cursor.close();
        db.close();
        return goal;

    }

目标是用（int,String,int,int,int,int,int,boolean,String）创建的。

下面是我对错误的logcat：

08-24 12:29:37.850: E/AndroidRuntime(7897): FATAL EXCEPTION: main
08-24 12:29:37.850: E/AndroidRuntime(7897): Process: com.lyncht.swimtracker, PID: 7897
08-24 12:29:37.850: E/AndroidRuntime(7897): android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.database.AbstractCursor.checkPosition(AbstractCursor.java:426)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.database.AbstractWindowedCursor.getInt(AbstractWindowedCursor.java:68)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.lyncht.swimtracker.DatabaseHandler.readGoalFromDb(DatabaseHandler.java:128)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.lyncht.swimtracker.ViewGoals.makeGoalsFromDB(ViewGoals.java:76)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.lyncht.swimtracker.ViewGoals.deleteGoal(ViewGoals.java:68)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.lyncht.swimtracker.ViewGoals.onContextItemSelected(ViewGoals.java:61)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.app.Activity.onMenuItemSelected(Activity.java:2620)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.android.internal.policy.impl.PhoneWindow$DialogMenuCallback.onMenuItemSelected(PhoneWindow.java:3864)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.android.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:741)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:884)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:874)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.android.internal.view.menu.MenuDialogHelper.onClick(MenuDialogHelper.java:167)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.android.internal.app.AlertController$AlertParams$3.onItemClick(AlertController.java:941)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.widget.AdapterView.performItemClick(AdapterView.java:299)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.widget.AbsListView.performItemClick(AbsListView.java:1113)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.widget.AbsListView$PerformClick.run(AbsListView.java:2911)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.widget.AbsListView$3.run(AbsListView.java:3645)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.os.Handler.handleCallback(Handler.java:733)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.os.Handler.dispatchMessage(Handler.java:95)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.os.Looper.loop(Looper.java:136)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at android.app.ActivityThread.main(ActivityThread.java:5001)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at java.lang.reflect.Method.invokeNative(Native Method)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at java.lang.reflect.Method.invoke(Method.java:515)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
08-24 12:29:37.850: E/AndroidRuntime(7897):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

在readgoalfromdb(int id)中

 Goal goal = null;
 if (cursor != null)
       if(cursor.moveToFirst()) // IMPORTANT!, check whether the returned cursor is empty
       {

           goal = new Goal(cursor.getInt(0), cursor.getString(1), cursor.getInt(2),
            cursor.getInt(3), cursor.getInt(4),
            cursor.getInt(5), Boolean.parseBoolean(cursor.getString(6)), cursor.getString(7));
            return goal;
        }
        else {
           //the returned cursor is empty
             Log.v("cursorempty","the cursor was returned empty");
             return null
        }

您检查了null，但没有检查游标是否有项。您只是尝试检索导致CursorIndexOutOfBoundsException的值。

如果返回的游标为空，则采取适当的操作

将MakeGoalsFromdb()修改为：

public void makeGoalsFromDB() {
        //looping through the table, get the goals and add them to the goals list
        goalsList = new ArrayList<Goal>(); 
        int goalsNo = db.getGoalsCount();
        for (int i = 1; i <= goalsNo; i++) { 
            if(null != db.readGoalFromDb(i)) 
            goalsList.add(db.readGoalFromDb(i));
        }
    }

Answer 2

就像Frank N.Stein已经说过的：你需要使用你想要删除的目标的数据库id。因此在onContextItemSelected中编写如下内容：

int idToDelete = listView.getItem(position).getGoalId();
deleteGoal(idToDelete);