Реализация класса, который расширяет SQLiteOpenHelper

Question

В принципе у меня есть два класса: один расширяет активность и другой SQLiteOpenHelper;

public class DatabaseHandler extends SQLiteOpenHelper { 

// All Static variables 
// Database Version 
private static final int DATABASE_VERSION = 1; 
DashboardActivity da; 
// Database Name 
private static final String DATABASE_NAME = "android_api"; 

// Login table name 
private static final String TABLE_LOGIN = "login"; 

// Login Table Columns names 
private static final String KEY_ID = "id"; 
private static final String KEY_NAME = "name"; 
private static final String KEY_EMAIL = "email"; 
private static final String KEY_UID = "uid"; 
private static final String KEY_CREATED_AT = "created_at"; 
public String emaili; 
public DatabaseHandler(Context context) { 
    super(context, DATABASE_NAME, null, DATABASE_VERSION); 
} 

// Creating Tables 
@Override 
public void onCreate(SQLiteDatabase db) { 
    String CREATE_LOGIN_TABLE = "CREATE TABLE " + TABLE_LOGIN + "(" 
      + KEY_ID + " INTEGER PRIMARY KEY," 
      + KEY_NAME + " TEXT," 
      + KEY_EMAIL + " TEXT UNIQUE," 
      + KEY_UID + " TEXT," 
      + KEY_CREATED_AT + " TEXT" + ")"; 
    db.execSQL(CREATE_LOGIN_TABLE); 
} 

// Upgrading database 
@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    // Drop older table if existed 
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_LOGIN); 

    // Create tables again 
    onCreate(db); 
} 

/** 
* Storing user details in database 
* */ 
public void addUser(String name, String email, String uid, String created_at) { 
    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    values.put(KEY_NAME, name); // Name 
    values.put(KEY_EMAIL, email); // Email 
    values.put(KEY_UID, uid); // Email 
    values.put(KEY_CREATED_AT, created_at); // Created At 

    // Inserting Row 
    db.insert(TABLE_LOGIN, null, values); 
    db.close(); // Closing database connection 
} 

/** 
* Getting user data from database 
* */ 
public HashMap<String, String> getUserDetails(){ 
    HashMap<String,String> user = new HashMap<String,String>(); 
    String selectQuery = "SELECT * FROM " + TABLE_LOGIN+"WHERE uid=9"; 

    SQLiteDatabase db = this.getReadableDatabase(); 
    Cursor cursor = db.rawQuery(selectQuery, null); 
    // Move to first row 
    cursor.moveToFirst(); 
    if(cursor.getCount() > 0){ 
     user.put("name", cursor.getString(1)); 
     user.put("email", cursor.getString(2)); 
     user.put("uid", cursor.getString(3)); 
     user.put("created_at", cursor.getString(4)); 
    } 
    emaili = getUserDetails().get("email"); 

    cursor.close(); 
    db.close(); 
    // return user 
    return user; 
} 

В моем классе активности Я пытаюсь получить значение метода String emaili onCreate как;

String email = db.emaili; 

После создания реализации класса SQLite сверху;

DatabaseHandler db; 

Ошибки:

02-06 07:06:38.772: E/AndroidRuntime(26874): FATAL EXCEPTION: main 
02-06 07:06:38.772: E/AndroidRuntime(26874): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.androidhive/com.example.androidhive.DashboardActivity}: java.lang.NullPointerException 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.app.ActivityThread.access$700(ActivityThread.java:143) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1241) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.os.Handler.dispatchMessage(Handler.java:99) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.os.Looper.loop(Looper.java:137) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.app.ActivityThread.main(ActivityThread.java:4950) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at java.lang.reflect.Method.invokeNative(Native Method) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at java.lang.reflect.Method.invoke(Method.java:511) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at dalvik.system.NativeStart.main(Native Method) 
02-06 07:06:38.772: E/AndroidRuntime(26874): Caused by: java.lang.NullPointerException 
02-06 07:06:38.772: E/AndroidRuntime(26874): at com.example.androidhive.DashboardActivity.onCreate(DashboardActivity.java:48) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.app.Activity.performCreate(Activity.java:5177) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094) 
02-06 07:06:38.772: E/AndroidRuntime(26874): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074) 

Вот класс DasboardActivity;

public class DashboardActivity extends Activity { 
UserFunctions userFunctions; 
Button btnLogout; 

DatabaseHandler db; 
Button btnFileUp; 
Button btnViewData; 





@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.dashboard); 
    // Buttons 
    /** 
    * Dashboard Screen for the application 
    * */   
    // Check login status in database 
    Button mondayEdit= (Button)findViewById(R.id.button1); 
     String email = db.emaili; 
     Log.i("EMAIL", ""+email); 
// email = db.getUserDetails()< 
    userFunctions = new UserFunctions(); 
    if(userFunctions.isUserLoggedIn(getApplicationContext())){ 
     setContentView(R.layout.dashboard); 

     btnViewData = (Button) findViewById(R.id.button1); 

     btnViewData.setOnClickListener(new View.OnClickListener() 
     { public void onClick(View v) 
      { 
       Intent intent = new Intent(getApplicationContext(), AllProductsActivity.class); 
       intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT); 
       startActivity(intent);  

        finish(); 
      } 
     }); 




     btnFileUp = (Button) findViewById(R.id.button2); 

     btnFileUp.setOnClickListener(new View.OnClickListener() 
     { public void onClick(View v) 
      { 
       Intent intent = new Intent(getApplicationContext(), FileUploadTest.class); 
       intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT); 
       startActivity(intent);  
        finish(); 
      } 
     }); 


     btnLogout = (Button) findViewById(R.id.btnLogout); 

     btnLogout.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View arg0) { 
       // TODO Auto-generated method stub 
       userFunctions.logoutUser(getApplicationContext()); 
       Intent login = new Intent(getApplicationContext(), LoginActivity.class); 
       login.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT); 
       startActivity(login); 
       // Closing dashboard screen 
       finish(); 
      } 
     }); 

    }else{ 
     // user is not logged in show login screen 
     Intent login = new Intent(getApplicationContext(), LoginActivity.class); 
     login.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
     startActivity(login); 
     // Closing dashboard screen 
     finish(); 
    } 




} 

public void onBackPressed(View v){ 
     Intent dashboard = new Intent(this, DashboardActivity.class); 
     dashboard.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
     dashboard.addFlags(Intent.FLAG_ACTIVITY_NO_HISTORY); 
    // Close all views before launching Dashboard 
     // this.finish(); 
     startActivity(dashboard); 
} 




} 

Answer 1

делает emaili вара статический, так что вы можете назвать его по имени класса

static String emaili=null; 

String email =db.emaili;