創建數據庫是給錯誤

Question

請看看下面的代碼

Form.java

Form.java是主要業務，這意味着對於Java文件第一頁。很多與創建「列表」和菜單相關的代碼都被刪除。

package com.example.esoftcallmanager; 

import android.os.Bundle; 
import android.app.Activity; 
import android.app.AlertDialog; 
import android.app.AlertDialog.Builder; 
import android.content.Context; 
import android.content.DialogInterface; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemClickListener; 
import android.widget.ArrayAdapter; 
import android.widget.ImageView; 
import android.widget.ListView; 
import android.widget.TextView; 

public class Form extends Activity { 



    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_form); 

     DatabaseConnector databaseConnector = new DatabaseHandler(); 
     databaseConnector.createConnection(); 

     ListView lv = (ListView)findViewById(android.R.id.list); 
     String arr[] = getResources().getStringArray(R.array.branch_list); 

     //lv.setAdapter(new MyAdapter(this,android.R.layout.simple_list_item_1,R.id.listText,arr)); 

     lv.setOnItemClickListener(new OnItemClickListener() { 
      @Override 
      public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, 
      long arg3) { 
      // TODO Auto-generated method stub 


      } 
      }); 
    } 
} 

DataBaseConnector.java

這是代碼的接口，它執行數據庫操作

package com.example.esoftcallmanager; 

public interface DatabaseConnector 
{ 
    public void createConnection(); 
    public void closeConnection(); 
    public String getPhoneNumber(); 
} 

DataBaseHandler.java

這是執行數據庫操作

package com.example.esoftcallmanager; 

import android.app.Activity; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.widget.Toast; 

public class DatabaseHandler extends Activity implements DatabaseConnector 
{ 
    private SQLiteDatabase database; 
    private String dbPath = "data//data//com.example.esoftcallmanager.sqllite//esoftDatabase"; 

    @Override 
    public void createConnection() 
    { 

     try 
     { 
      database = this.openOrCreateDatabase("esoftDatabase", MODE_PRIVATE, null); 

     database.execSQL("create table BranchNetwork(" + 
       "brID integer primary key autoincrement," 
       +"city text," 
       +"steetAddress text" 
       +"phoneNumber1 text" 
       +"phoneNumber2 text" 
       +"email text" 
       +");"); 
     } 
     catch(SQLException sql) 
     { 
      Toast.makeText(this, sql.getMessage(), Toast.LENGTH_LONG).show(); 
     } 

    } 

    @Override 
    public void closeConnection() { 
     // TODO Auto-generated method stub 

    } 

    @Override 
    public String getPhoneNumber() { 
     // TODO Auto-generated method stub 
     return null; 
    } 

} 

不過的人，我不能運行的代碼，因爲我收到以下錯誤。

02-11 20:35:59.350: D/dalvikvm(434): GC_EXTERNAL_ALLOC freed 52K, 53% free 2552K/5379K, external 1949K/2137K, paused 80ms 
02-11 20:40:34.021: D/dalvikvm(1131): GC_EXTERNAL_ALLOC freed 42K, 53% free 2552K/5379K, external 1949K/2137K, paused 122ms 
02-11 20:40:34.361: D/AndroidRuntime(1131): Shutting down VM 
02-11 20:40:34.361: W/dalvikvm(1131): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
02-11 20:40:34.401: E/AndroidRuntime(1131): FATAL EXCEPTION: main 
02-11 20:40:34.401: E/AndroidRuntime(1131): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.esoftcallmanager/com.example.esoftcallmanager.Form}: java.lang.NullPointerException 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.os.Handler.dispatchMessage(Handler.java:99) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.os.Looper.loop(Looper.java:123) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at java.lang.reflect.Method.invokeNative(Native Method) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at java.lang.reflect.Method.invoke(Method.java:507) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at dalvik.system.NativeStart.main(Native Method) 
02-11 20:40:34.401: E/AndroidRuntime(1131): Caused by: java.lang.NullPointerException 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at com.example.esoftcallmanager.DatabaseHandler.createConnection(DatabaseHandler.java:19) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at com.example.esoftcallmanager.Form.onCreate(Form.java:30) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
02-11 20:40:34.401: E/AndroidRuntime(1131):  ... 11 more 
02-11 20:40:37.381: I/Process(1131): Sending signal. PID: 1131 SIG: 9 

每當我從Form.java中刪除數據庫連接部分，這工作正常！所以錯誤必須在以下代碼中

DatabaseConnector databaseConnector = new DatabaseHandler(); 
     databaseConnector.createConnection(); 

我不想在Form.java中添加所有的數據庫操作。我需要像我那樣分工。但是，我該怎麼做？請幫忙！我看到

Answer 1

如果DatabaseHandler是非Activity類，則不需要將Activity擴展到它。您需要創建一個參數化的構造函數DatabaseHandler以將Activity上下文傳遞給它以創建數據庫。改變你的數據庫處理器類爲：

public class DatabaseHandler implements DatabaseConnector 
{ 
    private SQLiteDatabase database; 
    .... 
    Context context; 

    public DatabaseHandler(Context context){ 

     this.context=context; 
    } 

    @Override 
    public void createConnection() 
    { 

     try 
     { 
      database = context.openOrCreateDatabase("esoftDatabase", 
          MODE_PRIVATE, null); 
      // your code here.... 
     } 
     catch(SQLException sql) 
     { 
      Toast.makeText(context, sql.getMessage(), 
        Toast.LENGTH_LONG).show(); 
     } 

    } 

，並通過活動上下文從活動形式：

DatabaseConnector databaseConnector = 
        new DatabaseHandler(Form.this); 
databaseConnector.createConnection(); 

Answer 2

的一件事是：

database.execSQL("create table BranchNetwork(" + 
      "brID integer primary key autoincrement," 
      +"city text," 
      +"steetAddress text" 
      +"phoneNumber1 text" 
      +"phoneNumber2 text" 
      +"email text" 
      +");"); 

你必須寫：

database.execSQL("create table BranchNetwork(" + 
      "brID integer primary key autoincrement," 
      +"city text," 
      +"steetAddress text," //forgot comma 
      +"phoneNumber1 text," //forgot comma 
      +"phoneNumber2 text," // forgot commas 
      +"email text" 
      +");"); 

我不知道這是錯誤的，但嘗試...