Android：從數據庫中獲取Widget數據

Question

我想製作一個主屏幕部件，它顯示數據庫中的隨機收據。其實我在打開數據庫的命令時出錯了。

那麼，我能做些什麼來使它工作？通常這個代碼工作在一個正常的活動....但作爲小部件？

package com.droidfish.apps.acli; 

import java.util.Random; 

import android.appwidget.AppWidgetManager; 
import android.appwidget.AppWidgetProvider; 
import android.content.Context; 
import android.database.Cursor; 
import android.util.Log; 
import android.widget.RemoteViews; 
import android.widget.Toast; 

public class RecieptOfTheDayWidget extends AppWidgetProvider { 
static DataBaseHelper dbh; 

public void onDeleted(Context context, int[] appWidgetIds) { 
    // TODO Auto-generated method stub 
    super.onDeleted(context, appWidgetIds); 
    Toast.makeText(context, "widget deleted", Toast.LENGTH_SHORT).show(); 
} 

@Override 
public void onUpdate(Context context, AppWidgetManager appWidgetManager, 
     int[] appWidgetIds) { 
    // TODO Auto-generated method stub 
    super.onUpdate(context, appWidgetManager, appWidgetIds); 

    final int iN = appWidgetIds.length; 

    updateWidgetContent(context, appWidgetManager, appWidgetIds); 
} 

public static void updateWidgetContent(Context context, 
     AppWidgetManager appWidgetManager, int[] appWidgetIds) { 
    dbh.openDataBase(); 
    String sNameVariant = "basestring"; 
    Cursor c1 = dbh.rawQuery("SELECT _id from reciept"); 
    Random r = new Random(); 
    int iRandomID = 1; 
    int iVName = c1.getColumnIndex("name"); 
    int iCountDataSet; 
    for (c1.moveToFirst(); !c1.isAfterLast(); c1.moveToNext()) { 
     iCountDataSet = c1.getCount(); 
     iRandomID = r.nextInt(iCountDataSet); 
     Log.d("Random: ", (Integer.toString(iRandomID))); 

    } 
    Cursor c2 = dbh 
      .rawQuery("SELECT name FROM reciept WHERE _id = " 
        + iRandomID); 
    for (c2.moveToFirst(); !c2.isAfterLast(); c2.moveToNext()) { 
     sNameVariant = c2.getString(iVName); 
    } 
    RemoteViews vView1 = new RemoteViews(context.getPackageName(), 
      R.layout.recieptofthedaywidget); 

    vView1.setTextViewText(R.id.tvWidgetReciept, sNameVariant); 
    dbh.close(); 

    appWidgetManager.updateAppWidget(appWidgetIds, vView1); 
} 
} 

感謝彼得

更新＃1：
感謝柯蒂斯，

我加入你的方法是這樣

private static DataBaseHelper getDatabaseHelper(Context context) { 
    DataBaseHelper dbh = null; 
    if (dbh == null) { 
     dbh = new DataBaseHelper(context); 
     dbh.openDataBase(); 
    } 
    return dbh; 
} 

但現在收到這個錯誤

10-30 08:32:53.882: E/AndroidRuntime(296): java.lang.RuntimeException: Unable to start receiver com.droidfish.apps.acli.RecieptOfTheDayWidget: java.lang.IllegalStateException: get field slot from row 0 col -1 failed 

它看起來像它無法從列數的範圍內的隨機數。這是正確的嗎？其實它產生同樣的錯誤，當我寫

iRandomID = r.nextInt(3); 

Mhh這真的很有趣。有什麼建議麼？

更新＃2：
我改變了這樣的代碼和它的工作。有缺失索姆重要的行:)）））

再次感謝

 Cursor c1 =getDatabaseHelper(context).getReadableDatabase().rawQuery("SELECT _id from reciept_variant", null); 
    Random r = new Random(); 
    int iRandomID = 1; 
    int iVName = c1.getColumnIndex("_id"); 
    int iCountDataSet; 
    for (c1.moveToFirst(); !c1.isAfterLast(); c1.moveToNext()) { 
     iCountDataSet = c1.getCount(); 
     //iRandomID = r.nextInt(3); 
     iRandomID = r.nextInt(iCountDataSet); 
     Log.d("Random: ", (Integer.toString(iRandomID))); 

    } 
    Cursor c2 = getDatabaseHelper(context).getReadableDatabase().rawQuery("SELECT _id, name FROM reciept_variant WHERE _id = 3" 
       , null); 

    int iName2 = c2.getColumnIndex("name"); 
    for (c2.moveToFirst(); !c2.isAfterLast(); c2.moveToNext()) { 
     sNameVariant = c2.getString(iName2); 
    } 

Answer 1

彼得，它看起來像你從來沒有初始化數據庫輔助類。因此它被設置爲null，你可能會得到一個空指針異常。嘗試添加以下代碼：

private static DataBaseHelper getDatabaseHelper(){ 
    if(dbh==null){ 
    dbh = new DatabaseHelper(/* put your database helper arguments here */); 
    dbh.openDatabase(); 
    } 
    return dbh; 
} 

然後，每當你需要使用的胸徑，你叫getDatabaseHelper。例如，在你的updateWidgetContent（）方法中執行此操作：

Cursor c1 = getDatabaseHelper().getReadableDatabase().rawQuery("SELECT _id from reciept");