爲什麼我每次向sqlite數據庫添加新表時都必須增加數據庫版本？

Question

這是我的數據庫創建的地方。我使用了一個全局變量，它在登錄時接受用戶名，然後我根據該用戶名創建一個表。 當我嘗試輸入數據到數據庫時，它給了我一個錯誤，說沒有這樣的表存在。如果我手動增加數據庫版本，它的工作原理！每次創建新表時，是否必須增加數據庫版本？如果是這樣，我怎麼能做到這一點？

非常時間一個新用戶註冊一個新表添加來保存用戶信息，在調試時，我必須手動進入我的代碼並增加數據庫版本，每次添加一個新用戶時，有沒有更好的方法這樣做？否則，用戶將能夠登錄，但將無法輸入任何信息，直到我進入我的代碼，並增加數據庫版本..謝謝

package com.example.victor.kidsrewards; 
import android.app.Activity; 
import android.content.Context; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 
import android.content.Intent; 
import android.os.Bundle; 

/** 
* Created by Victor on 3/20/2016. 
*/ 
public class TaskSQLiteHelper extends SQLiteOpenHelper { 
    String _username = Globals._username; 

    public TaskSQLiteHelper(Context context){ 
     super(context, "tasks_db", null, 8); 

    } 


    @Override 
    public void onCreate(SQLiteDatabase db) { 
     //create a table 

     db.execSQL("CREATE TABLE tasks_"+_username + " (_id INTEGER PRIMARY KEY , task TEXT NOT NULL, points INTEGER NOT NULL)"); 
    } 

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

} 

這是我的跟蹤

03-30 14:18:25.217 6450-6450/com.example.victor.kidsrewards E/SQLiteLog: (1) no such table: tasks_JOE 
03-30 14:18:25.217 6450-6450/com.example.victor.kidsrewards D/AndroidRuntime: Shutting down VM 
03-30 14:18:25.221 6450-6450/com.example.victor.kidsrewards W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x94d5eb20) 
03-30 14:18:25.221 6450-6450/com.example.victor.kidsrewards E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.example.victor.kidsrewards, PID: 6450 
android.database.sqlite.SQLiteException: no such table: tasks_JOE (code 1): , while compiling: SELECT _id, task, points FROM tasks_JOE 
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method) 
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889) 
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500) 
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588) 
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58) 
at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37) 
at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44) 
at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1314) 
at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1161) 
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1032) 
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1200) 
at com.example.victor.kidsrewards.TaskDataBase.getTasks(TaskDataBase.java:59) 
at com.example.victor.kidsrewards.TaskList.onActivityCreated(TaskList.java:46) 
at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1983) 
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1092) 
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252) 
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738) 
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617) 
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517) 
at android.os.Handler.handleCallback(Handler.java:733) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:136) 
at android.app.ActivityThread.main(ActivityThread.java:5045) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
at dalvik.system.NativeStart.main(Native Method) 

Answer 1

爲了在Android中升級數據庫，您應該將DATABASE_VERSION增加1，以便SQLOpenHelper知道它必須調用onUpgrade方法。

否則你的表不會添加和舊的數據庫將被使用。