單擊按鈕（SQLite數據庫）後空指針異常

Question

我得到一個空指針異常，當我點擊確認按鈕將數據保存到sqlite數據庫時，我的應用程序關閉。我真的不知道這裏有什麼問題......

public class Morfologia extends Activity { 

    DatabaseAdapter dbAdapter2; 


    private EditText editTextHem; 

    private Button button10; 

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

     editTextHem = (EditText) findViewById(R.id.editText1_hemoglobina); 
     button10 = (Button) findViewById(R.id.button1_morfologia); 
     button10.setOnClickListener(l2); 

    } 

    private OnClickListener l2 = new OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      if (v.getId() == R.id.button1_morfologia){ 
       saveToDB(); 
      } 

     } 
    }; 


    public void saveToDB() { 

     String hemoglobina = editTextHem.getText().toString(); 
     Log.d("text: ", hemoglobina); 

     dbAdapter2.open(); 
     dbAdapter2.insertMorphologyData(hemoglobina); 
     dbAdapter2.close(); 
    }} 

的logcat：

11-04 10:49:37.734: D/text:(21197): 123 
11-04 10:49:37.734: D/AndroidRuntime(21197): Shutting down VM 
11-04 10:49:37.734: W/dalvikvm(21197): threadid=1: thread exiting with uncaught exception (group=0x416ced40) 
11-04 10:49:37.736: E/AndroidRuntime(21197): FATAL EXCEPTION: main 
11-04 10:49:37.736: E/AndroidRuntime(21197): Process: com.example.bmicalculator, PID: 21197 
11-04 10:49:37.736: E/AndroidRuntime(21197): java.lang.NullPointerException 
11-04 10:49:37.736: E/AndroidRuntime(21197): at com.example.bmicalculator.Morfologia.saveToDB(Morfologia.java:54) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at com.example.bmicalculator.Morfologia$1.onClick(Morfologia.java:42) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at android.view.View.performClick(View.java:4456) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at android.view.View$PerformClick.run(View.java:18465) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at android.os.Handler.handleCallback(Handler.java:733) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at android.os.Handler.dispatchMessage(Handler.java:95) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at android.os.Looper.loop(Looper.java:136) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at android.app.ActivityThread.main(ActivityThread.java:5086) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at java.lang.reflect.Method.invokeNative(Native Method) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at java.lang.reflect.Method.invoke(Method.java:515) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 
11-04 10:49:37.736: E/AndroidRuntime(21197): at dalvik.system.NativeStart.main(Native Method) 

類具有saveToDB方法：

package com.example.bmicalculator.database; 



public class DatabaseAdapter { 

    SQLiteDatabase database; 
    DatabaseOpenHelper dbHelper; 

    public DatabaseAdapter(Context context) { 
     dbHelper = new DatabaseOpenHelper(context); 
    } 

    public void open() { 
     database = dbHelper.getWritableDatabase(); 
    } 

    public void close() { 
     database.close(); 
    } 




    public void insertMorphologyData(String hemoglobina){ 
     ContentValues values2 = new ContentValues(); 
     values2.put("hemoglobina", hemoglobina); 
     database.insert("morfologia_krwi2", null, values2); 
    } 



} 

類創建表：

public class DatabaseOpenHelper extends SQLiteOpenHelper { 

    public static final String dbName = "baza"; 


    public static final String morphologyTableName = "morfologia_krwi2"; 

    public static final String createTableMorphology = "CREATE TABLE " + morphologyTableName + 
      "(id INTEGER PRIMARY KEY AUTOINCREMENT," + 
      "hemoglobina TEXT);"; 


    public DatabaseOpenHelper(Context context) { 
     super(context, dbName, null, 1); 
     // TODO Auto-generated constructor stub 
    } 


    @Override 
    public void onCreate(SQLiteDatabase database) { 
     // TODO Auto-generated method stub 
     database.execSQL(createTableMorphology); 


    } 


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

    } 



} 

Answer 1

你只宣佈你的dbadapter2但從未初始化它。

使用

dbadapter2 = new DatabaseAdapter(this); 

對其進行初始化，其中this是例如你的Activity這是一個Context。