在sqlite數據庫中插入數據到數據庫時出現NullPointerException

Question

在sqlite數據庫中插入數據時，我得到NullPointerException 請幫我解決這個問題。它在插入方法中顯示錯誤。

DatabaseHelper.java

package com.example.mydbdemo; 

    import com.example.mydbdemo.R.string; 

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

    public class DatabaseHelper extends SQLiteOpenHelper { 

     private static final String DB_NAME="reena.db"; 
     private static final String TBL_NAME="MY_TBL"; 

     private static final String User_Name="name"; 
     private static final String Mobile_No="mobile"; 

     public DatabaseHelper(Context context, String name, CursorFactory factory, 
       int version) { 
      super(context, name, factory, version); 
      // TODO Auto-generated constructor stub 
     } 

     @Override 
     public void onCreate(SQLiteDatabase db) { 
      // TODO Auto-generated method stub 

      //CREATE TABLE 
     db.execSQL("CREATE TABLE"+TBL_NAME+"("+User_Name+" TEXT, "+Mobile_No+" TEXT)"); 
     } 

     @Override 
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
      // TODO Auto-generated method stub 

     } 


     void insert_user(String name1, String num) 
     { 
      SQLiteDatabase mydb=this.getWritableDatabase(); 
      ContentValues cv=new ContentValues(); 

      cv.put(User_Name, name1); 
      cv.put(Mobile_No, num); 
      mydb.insert(TBL_NAME, null, cv); 
     } 
    } 

MyDBDemo.java

package com.example.mydbdemo; 

    import android.os.Bundle; 
    import android.app.Activity; 
    import android.database.sqlite.SQLiteDatabase; 
    import android.view.Menu; 
    import android.view.View; 
    import android.widget.Button; 
    import android.widget.EditText; 
    import android.widget.Toast; 

    public class MyDBDemo extends Activity { 

     EditText txt_NAME; 
     EditText txt_PH; 
     Button btn_Ok; 
     DatabaseHelper dbHelper; 
     SQLiteDatabase db; 

     @Override 
     public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.activity_my_dbdemo); 

      txt_NAME=(EditText)findViewById(R.id.txt_Name); 
      txt_PH=(EditText)findViewById(R.id.txt_Moblie); 
      btn_Ok=(Button)findViewById(R.id.button1); 
      btn_Ok.setOnClickListener(new View.OnClickListener() { 

       @Override 
     public void onClick(View v) { 
        // TODO Auto-generated method stub 
        insert(); 
       } 
      }); 
     } 

     @Override 
     public boolean onCreateOptionsMenu(Menu menu) { 
      getMenuInflater().inflate(R.menu.activity_my_dbdemo, menu); 
      return true; 
     } 


     public void insert() 
     { 
      String name=txt_NAME.getText().toString(); 
      String mobile=txt_PH.getText().toString(); 
      dbHelper.insert_user(name, mobile); 
      Toast.makeText(getApplicationContext(), "Data Saved Successfully!!", Toast.LENGTH_LONG).show(); 


     } 
    } 

logcat的

03-02 11:38:04.118: E/AndroidRuntime(371): FATAL EXCEPTION: main 
03-02 11:38:04.118: E/AndroidRuntime(371): java.lang.NullPointerException 
03-02 11:38:04.118: E/AndroidRuntime(371): at com.example.mydbdemo.MyDBDemo.insert(MyDBDemo.java:51) 
03-02 11:38:04.118: E/AndroidRuntime(371): at com.example.mydbdemo.MyDBDemo$1.onClick(MyDBDemo.java:33) 
03-02 11:38:04.118: E/AndroidRuntime(371): at android.view.View.performClick(View.java:2408) 
03-02 11:38:04.118: E/AndroidRuntime(371): at android.view.View$PerformClick.run(View.java:8816) 
03-02 11:38:04.118: E/AndroidRuntime(371): at android.os.Handler.handleCallback(Handler.java:587) 
03-02 11:38:04.118: E/AndroidRuntime(371): at android.os.Handler.dispatchMessage(Handler.java:92) 
03-02 11:38:04.118: E/AndroidRuntime(371): at android.os.Looper.loop(Looper.java:123) 
03-02 11:38:04.118: E/AndroidRuntime(371): at android.app.ActivityThread.main(ActivityThread.java:4627) 
03-02 11:38:04.118: E/AndroidRuntime(371): at java.lang.reflect.Method.invokeNative(Native Method) 
03-02 11:38:04.118: E/AndroidRuntime(371): at java.lang.reflect.Method.invoke(Method.java:521) 
03-02 11:38:04.118: E/AndroidRuntime(371): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
03-02 11:38:04.118: E/AndroidRuntime(371): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
03-02 11:38:04.118: E/AndroidRuntime(371): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

需要初始化你Dbhelpers ..裏面插入寫（）DB = dbHelper.getWritableDatabase（） ;並初始化dbHelper類。

Answer 2

因爲，你DatabaseHelper dbHelper;是NULL。

裏面insert()方法。

所以代碼行dbHelper.insert_user(name, mobile);給你空指針異常。

解決方案：

初始化DatabaseHelper dbHelper;訪問它。

Answer 3

你應該intialize您DatabaseHleper，目前其空

此行拋出NullPointerException

dbHelper.insert_user(name, mobile);