Android第二个表未创建

Question

首先我创建了一个表，它工作。第二个我以同样的方式做，仍然给出错误：没有这样的表 my_contacts。

所以这是代码：

[在主要活动中]

DBOperations.insert(this, TABLE_MY_CONTACTS, fields, vals);

DBOperations 类如下所示：

public class DBOperations implements Tables {

// inserting 1 contact into a table
public static boolean insert (Context context, String table, ArrayList <String> fields, ArrayList <String> vals) {

    if (fields.size() != vals.size())
        return false;

    MySQLite_methods mysql = new MySQLite_methods (context, table); // creates the table!!!!!!!!!
    ContentValues values = new ContentValues();

    for (int i=0; i<fields.size(); i++)
        values.put(fields.get(i), vals.get(i));

    // checking if the card for that ulink already existed (if so, overwrite)
    String[] COLUMNS = {ULINK};
    SQLiteDatabase dbr = mysql.getReadableDatabase();
    Cursor cursor = dbr.query(table, COLUMNS, null, null, null, null, null);

    SQLiteDatabase dbw = mysql.getWritableDatabase();
    if (cursor == null || cursor.moveToFirst() == false)                
         dbw.insertOrThrow(table, null, values);
    else
        if (cursor.moveToFirst()) {
            String value_ulink = cursor.getString(0);
            Log.d("geo", "val="+value_ulink);
            dbw.update(table, values, ULINK+"='"+value_ulink+"'", null);
        }

    return true;
}

    // ....
}

MySQLite_methods 类扩展了 SQLiteOpenHelper，如下所示：

公共类 MySQLite_methods 扩展 SQLiteOpenHelper 实现表 {

private static final String DATABASE_NAME = "my_database.db" ;
private static final int DATABASE_VERSION = 1;
private String TABLE_NAME;

/** Create a helper object for the Events database */
public MySQLite_methods (Context ctx, String table_name) 
{
    super(ctx, DATABASE_NAME, null, DATABASE_VERSION);
    this.TABLE_NAME = table_name;
}

@Override
public void onCreate(SQLiteDatabase db) 
{       
    String sql = "CREATE TABLE IF NOT EXISTS " + TABLE_NAME + 
                    " (" + _ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +               
                    NAME + " TEXT NOT NULL," + 
                    PHONE + " TEXT NOT NULL,"+
                    EMAIL + " TEXT NOT NULL,"+                      
                    FACEBOOK + " TEXT,"+
                    WEBSITE + " TEXT,"+
                    MAJOR + " TEXT NOT NULL,"+
                    ULINK + " TEXT NOT NULL" + ");" ;

    Log.d("geo", sql);

    db.execSQL(sql);
}

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

}

最后界面 Tables 是这样的：

public interface Tables extends BaseColumns {

/*
 * From the BaseColumns interface we inherit the constants:
 * _ID - The unique ID for a row.
 * _COUNT - The count of rows in a directory.
 */

//tables name
public static final String TABLE_MY_CARD= "my_card" ;
public static final String TABLE_MY_CONTACTS = "my_contacts" ;

// Columns
public static final String NAME = "name" ;
public static final String PHONE = "phone" ;
public static final String EMAIL = "email";

public static final String FACEBOOK = "facebook";
public static final String WEBSITE = "web";
public static final String MAJOR = "major";
public static final String ULINK = "ulink";

}

使用相同的步骤，我创建了另一个成功的表。但是这个我根本无法创建！

Answer 1

我认为 onUpgrade 和 onCreate 并没有按照你想象的方式执行。

onCreate 只会在需要创建 DB 文件时执行。

onUpgrade 根据需要执行（即 newVersion > oldVersion）

我相信正在发生的事情是因为 onCreate 执行而创建了第一个表，因为数据库还不存在。然后，当您尝试创建第二个表时，它不起作用，因为既没有调用 onCreate 也没有调用 onUpgrade。

您应该在 onCreate 期间创建所有表并处理 onUpgrade 期间所需的任何升级逻辑。