database.CursorIndexOutOfBoundsException：索引0請求，大小爲0

Question

我想訪問數據庫，但它工作得更早，但現在它不工作bcoz表沒有值和它的空，誰能告訴我如何處理這個異常？我的應用程序崩潰每次我嘗試訪問平衡方法來獲得平衡的列值

 package com.example.bipinp.mithun; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 

import java.util.ArrayList; 
import java.util.List; 

/** 
* Created by Bipinp on 2/18/2016. 
*/ 
public class DatabaseHelper extends SQLiteOpenHelper { 
    public static final String DATABASE_NAME = "Sales.db"; 
    public static final String TABLE_NAME1 = "Insert_table"; 
    public static final String TABLE_NAME2 = "Entry_table"; 

    public static final String COL_ID = "ID"; 
    public static final String COL_NAME = "NAME"; 

    public static final String COL_CUST_NAME = "NAME"; 
    public static final String COL_CARET = "CARET"; 
    public static final String COL_AMOUNT = "AMOUNT"; 
    public static final String COL_AMOUNT_PAID = "AMOUNT_PAID"; 
    public static final String COL_BALANCE = "BALANCE"; 

    public DatabaseHelper(Context context) { 
     super(context, DATABASE_NAME, null, 1); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) { 
     db.execSQL("create table " + TABLE_NAME1 + " (ID INTEGER PRIMARY KEY AUTOINCREMENT,NAME TEXT)"); 
     db.execSQL("create table " + TABLE_NAME2 + " (ID INTEGER PRIMARY KEY AUTOINCREMENT,NAME TEXT,CARET INTEGER,AMOUNT INTEGER,AMOUNT_PAID INTEGER,BALANCE INTEGER,FOREIGN KEY(ID) REFERENCES Insert_table(ID_NAME))"); 

    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     db.execSQL("DROP TABLE IF EXISTS" + TABLE_NAME1); 
     db.execSQL("DROP TABLE IF EXISTS" + TABLE_NAME2); 
     onCreate(db); 

    } 

    public boolean deleteRow(String name) 
    { SQLiteDatabase db = this.getWritableDatabase(); 
     return db.delete(TABLE_NAME1, COL_NAME + "= '" + name + "';", null) > 0; 
    } 

    public boolean insertdata(String name){ 
     SQLiteDatabase db = this.getWritableDatabase(); 
     ContentValues contentValues = new ContentValues(); 
     contentValues.put(COL_NAME,name); 
     long result = db.insert(TABLE_NAME1,null,contentValues); 
     if(result == -1) 
      return false; 
     else 
      return true; 
    } 

    public boolean insertdata2(String name,String caret,String amount,String amount_paid,String balance){ 
     SQLiteDatabase db = this.getWritableDatabase(); 
     ContentValues contentValues = new ContentValues(); 
     contentValues.put(COL_CUST_NAME,name); 
     contentValues.put(COL_CARET,caret); 
     contentValues.put(COL_AMOUNT,amount); 
     contentValues.put(COL_AMOUNT_PAID,amount_paid); 
     contentValues.put(COL_BALANCE,balance); 
     long result = db.insert(TABLE_NAME2,null,contentValues); 
     if (result == -1) 
      return false; 
     else 
      return true; 
    } 

    public List<String> getAllLabels(){ 
     List<String> labels = new ArrayList<String>(); 

     String selectQuery = " SELECT " + COL_NAME + " FROM " + TABLE_NAME1; 
     SQLiteDatabase db = this.getReadableDatabase(); 
     Cursor cursor = db.rawQuery(selectQuery,null); 

     if (cursor.moveToFirst()){ 
      do { labels.add(cursor.getString(0)); 
      }while (cursor.moveToNext()); 
     } 
     cursor.close(); 
     db.close(); 

     return labels; 
    } 
    public String balance(String name) 
    { 
     String label = null; 
     SQLiteDatabase db = this.getReadableDatabase(); 
     String selectQuery = " SELECT " + COL_BALANCE + " FROM " + TABLE_NAME2 + " WHERE " + COL_CUST_NAME + "= '" + name + "';"; 
     Cursor cursor = db.rawQuery(selectQuery,null); 

     if(cursor != null) 
     { 
      cursor.moveToFirst(); 
      label = cursor.getString(0); 
      cursor.close(); 
     } 

     return label; 
    } 


} 

Answer 1

在你的平衡功能，你認爲光標具有第一項。它可能不會。您需要將其更改爲

if(cursor != null) 
    { 
     if(cursor.moveToFirst()){ 
      label = cursor.getString(0); 
     } 
     cursor.close(); 
    } 

並確保您可以處理來自平衡返回null（）