java - Helloworld 数据库 - Android 与 sqlite 的连接

Question

我是 Android 新手。我只需要编写一个简单的 hello-world 应用程序，该应用程序在屏幕上显示有关该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。

主要:

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);
    }
}

数据库助手:

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

我想阿迪尔想说这些..

----------


/**open the db**/   


----------


 DbHelper = new DatabaseHelper(context);

db = mDbHelper.getWritableDatabase();

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