我正在为Android进行登录和注册，但是我使用的sqlite数据库在onCreate上崩溃了

Question

package company.mystorage.com.mystorage;

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{

private static final String DATABASE_NAME = "mystorage.db";
private static final String TABLE_NAME = "userlist";

public static final String COLUMN_1 ="Id";
private static final String COLUMN_2 = "username";
private static final String COLUMN_3 = "password";
SQLiteDatabase db;

    public DatabaseHelper(Context context) {
        // database is created when constructor is called.
        super(context, DATABASE_NAME, null, 1);
        // to invoke onCreate() and onUpgrade() methods to create the tables
        SQLiteDatabase db = this.getWritableDatabase();

    }

    @Override
    public void onCreate(SQLiteDatabase db){
        db.execSQL("create table " + TABLE_NAME + "("
                + COLUMN_1 +" INTEGER PRIMARY KEY AUTOINCREMENT, "
                + COLUMN_2 +" TEXT, "
                + COLUMN_3 +" TEXT)"
        );

    }

    public boolean insertData(String username, String password){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(COLUMN_2, username);
        contentValues.put(COLUMN_3, password);
        long result = db.insert(TABLE_NAME, null, contentValues);
        if (result == -1)
            return false;
        else
            return true;
    }

    public boolean searchPass(String user){
        db = this.getReadableDatabase();
        String query = "select * from  " + TABLE_NAME + " where " + COLUMN_2 + " = " + "'" + user + "'";
        Cursor cursor = db.rawQuery(query, null);

        cursor.moveToFirst();
        if (cursor.getCount() > 0) {

            return true;
        }
        cursor.close();
        db.close();

        return false;

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS "+ TABLE_NAME);
        onCreate(db);
    }

}

This code will create a database and also contains the functions to search and add users to the database. I tried to debug the code and it showed that it crashed when the onCreate was called. I checked the onCreate but the query is being execute correctly.

Edited* I changed the this. for the db but it still crashed.

Answer 1

 public void onCreate(SQLiteDatabase db){ this.db.execSQL(...) 

You should be calling execSQL() on the db parameter and not this.db field that has not yet been initialized.

Answer 2

This should help :

 public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL_CREATE_ENTRIES);
    }

Please remove "this".

Also, in your method SearchPass(), if cursor has more count than it wont close the cursor and db object. It would be a better idea to handle that in Finally block.

Answer 3

在您的onCreate方法中，请勿将this与db.execSQL(..)