在Android的初始屏幕上创建数据库

Question

我的应用程序中有一个启动画面，我正在检查我的数据库的表是否存在，如果没有，请创建我的应用程序需要的表。我的想法是让2次的检查，像这样：

if(db.exists){ 
increase the progressbar to the 100% 
(If we could add a short pause to the progress bar transition better, just 
for a better user experience)} 

else{ 
increase the progress bar to 50% and create databases. By last increase 
progress bar to 100%} 

start -> main_activity 

这只是我有这个想法，但我不知道如何构建和我不如何引用AppSQLiteHelper.java的方法。如果你们中的任何人有更好的想法来更好地改进代码逻辑。下面是写，直到此刻代码：

SplashScreenActivity.java：

public class SplashScreenActivity extends Activity { 

// Set the duration of the splash screen 
public ProgressBar splash_screenProgressBar; 
public int MAX_VALUE = 30; 


@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    // Set portrait orientation 
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT); 
    setContentView(R.layout.splash_screen); 

    splash_screenProgressBar = (ProgressBar) findViewById(R.id.splash_screenProgressBar); 
    splash_screenProgressBar.setMax(MAX_VALUE); 

    new CountDownTimer(3000, 100) { 

     int progreso = 1; // Variable que va a ir aumentando del progreso 
     @Override 
     public void onTick(long millisUntilFinished) { 
      splash_screenProgressBar.setProgress(progreso); 
      progreso += (1); 
     } 

     @Override 
     public void onFinish() { 
      splash_screenProgressBar.setProgress(MAX_VALUE); 

      // Start the next activity 
      Intent mainIntent = new Intent().setClass(SplashScreenActivity.this, MainActivity.class); 
      startActivity(mainIntent); 

      // Close the activity so the user won't able to go back this activity pressing Back button 
      finish(); 
     } 
    }.start(); 
} 

} 

AppSQLiteHelper.java：

public class AppSQLiteHelper extends SQLiteOpenHelper{ 

String sqlCreateCartera = "CREATE TABLE CARTERA (saldo INTEGER)"; 
String sqlCreateValor = "CREATE TABLE VALOR (cantidad INTEGER, precio_accion INTEGER, entidad TEXT)"; 
String sqlCreateEstado = "CREATE TABLE ESTADO (estado BOOLEAN)"; 

public AppSQLiteHelper(Context contexto, String nombre, 
          CursorFactory factory, int version) { 
    super(contexto, nombre, factory, version); 
} 

@Override 
public void onCreate(SQLiteDatabase db) { 
    db.execSQL(sqlCreateCartera); 
    db.execSQL(sqlCreateValor); 
    db.execSQL(sqlCreateEstado); 
} 

@Override 
public void onUpgrade(SQLiteDatabase db, int versionAnterior, int versionNueva) { 
    db.execSQL("DROP TABLE IF EXISTS CARTERA"); 
    db.execSQL("DROP TABLE IF EXISTS VALOR"); 
    db.execSQL("DROP TABLE IF EXISTS ESTADO"); 

    db.execSQL(sqlCreateCartera); 
    db.execSQL(sqlCreateValor); 
    db.execSQL(sqlCreateEstado); 
} 

} 

Answer 1

为什么要是否存在检查DB与否，因为一旦当你创建你的对象AppSQLiteHelper ..它会自动调用onCreate()的重写函数来初始化数据库，你不必明确检查它是否存在。如果你真的想这样做，尽管有上述条件，那么你可以创建一个callb ACK界面和您的辅助类和你的OnCreate执行后，你可以实现检查其是否创建低于db.Like ..

public interface OnDBInitializeListener { 
    public void onCreateCalled(int position); 
} 

并使用此当你通过传递这对constructor..Hope叫助手类这有助于