Question

我是Android的新开发者。我需要编写一个简单的hello-world应用程序，在屏幕上显示有关应用程序所连接的数据库的一些数据。这是我的尝试，但它在“选择或显示”部分崩溃。它由两个文件组成：Main和DataBaseHelper。

主：

package com.SQLearning;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class HelloTestSQLActivity extends Activity {
    DatabaseHelper dbHelper;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.main);

        int seats = dbHelper.getSeats("2");
        TextView tv = new TextView(this);
        setContentView(tv);
        tv.setText( "My first Android App: This is a Hello World Test..." +
                "Database connection in progress..." +
                "Table 2 has "+seats);
    }
}

DataBaseHelper：

package com.SQLearning;

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

public class DatabaseHelper extends SQLiteOpenHelper {

    static final String dbName="demoDB";
    static final String tablesTable="Tables";
    static final String colNum="TableNum";
    static final String colSeats="NumSeats";

    static final String viewTables="ViewTables";

    public DatabaseHelper(Context context) {
      super(context, dbName, null,2); 
}

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

      db.execSQL("CREATE TABLE "+tablesTable+" ("+colNum+ " INTEGER PRIMARY KEY , "+
                                                colSeats+ " INTEGER)");


      db.execSQL("CREATE VIEW "+viewTables+
                " AS SELECT "+tablesTable+"."+colNum+" AS _id,"+
                " "+tablesTable+"."+colSeats+","+
                " FROM "+tablesTable);

      //Inserts pre-defined departments
      insertTableRecords();
}

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

      db.execSQL("DROP TABLE IF EXISTS "+tablesTable);
      db.execSQL("DROP VIEW IF EXISTS "+viewTables);
      onCreate(db);
     }

public void insertTableRecords() {
    SQLiteDatabase db=this.getWritableDatabase();
    ContentValues cv=new ContentValues();

    cv.put(colNum, 1);
    cv.put(colSeats, 3);
    db.insert(tablesTable, colNum, cv);

    cv.put(colNum, 2);
    cv.put(colSeats, 6);
    db.insert(tablesTable, colNum, cv);

    cv.put(colNum, 3);
    cv.put(colSeats, 5);
    db.insert(tablesTable, colNum, cv);

    cv.put(colNum, 4);
    cv.put(colSeats, 2);
    db.insert(tablesTable, colNum, cv);

    db.close();
}

public int getSeats(String tablenum)
  {
   SQLiteDatabase db=this.getReadableDatabase();

   String[] args = new String[] {"1"};
   Cursor cur = db.rawQuery(" SELECT "+colSeats+" FROM "+tablesTable+" WHERE "+colNum+"=? ", args);

   cur.moveToFirst();
   db.close();

   //return cur.getInt(cur.getColumnIndex(colSeats));
   return cur.getInt(0);

  }

}

提前致谢。

Answer 1

我认为阿迪尔想说出这件事......

----------


/**open the db**/   


----------


 DbHelper = new DatabaseHelper(context);

db = mDbHelper.getWritableDatabase();

/**Closes the OLQ Database*/
public void closeOLQ() 
{
    mDbHelper.close();
}

Helloworld数据库 - 与sqlite的android连接

1 个答案: