Android 内容提供商

发布于 2024-09-26 08:15:16 字数 110 浏览 5 评论 0原文

我想获取创建数据库的内容提供商的代码。我正在使用位于此处的工具 tools/sqllite3.exe 来检查数据库是否已创建。

请让我知道这件事的逐步程序...

谢谢， -D

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多孤肩上扛 2024-10-03 08:15:16

您不使用 ContentProvider 来创建数据库，而是使用 SQLiteOpenHelper 类来创建数据库。至少这是更好的方法，

class MyDatabase extends SQLiteOpenHelper {
    public MyDatabase(Context context, dbName, null, version){
        super(context, dbName, null, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        String createItemsTable = "create table mytable ("+
            "_id INTEGER PRIMARY KEY AUTOINCREMENT, " +
            "_title TEXT NOT NULL, " +
            "_subtitle TEXT NULL " +
        " );";

        // Begin Transaction
        db.beginTransaction();
        try{
            // Create Items table
            db.execSQL(createItemsTable);

            // Transaction was successful
            db.setTransactionSuccessful();
        } catch(SQLException ex){
            Log.e(this.getClass().getName(), ex.getMessage(), ex);
        } finally {
            // End transaction
            db.endTransaction();
        }
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        String dropItemsTable = "DROP TABLE IF EXISTS mytable";

        // Begin transaction
        db.beginTransaction();

        try {
            if(oldVersion<2){
                // Do your update/alter code here
            }

            db.setTransactionSuccessful();
        } catch(Exception ex){
            Log.e(this.getClass().getName(), ex.getMessage(), ex);
        } finally {
            // Ends transaction
            // If there was an error, the database won't be altered
            db.endTransaction();
        }
    }
}

他们只需使用实例化您的助手

MyDatabase myDb = new MyDatabase(getContext(),"databasename.db", null, 1);

然后助手将创建数据库（如果不存在），如果旧版本存在则升级它，或者如果存在并且版本匹配则简单地打开它

You don't crate the database with the ContentProvider, but with the SQLiteOpenHelper class. At least that's the better way of doing it

class MyDatabase extends SQLiteOpenHelper {
    public MyDatabase(Context context, dbName, null, version){
        super(context, dbName, null, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        String createItemsTable = "create table mytable ("+
            "_id INTEGER PRIMARY KEY AUTOINCREMENT, " +
            "_title TEXT NOT NULL, " +
            "_subtitle TEXT NULL " +
        " );";

        // Begin Transaction
        db.beginTransaction();
        try{
            // Create Items table
            db.execSQL(createItemsTable);

            // Transaction was successful
            db.setTransactionSuccessful();
        } catch(SQLException ex){
            Log.e(this.getClass().getName(), ex.getMessage(), ex);
        } finally {
            // End transaction
            db.endTransaction();
        }
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        String dropItemsTable = "DROP TABLE IF EXISTS mytable";

        // Begin transaction
        db.beginTransaction();

        try {
            if(oldVersion<2){
                // Do your update/alter code here
            }

            db.setTransactionSuccessful();
        } catch(Exception ex){
            Log.e(this.getClass().getName(), ex.getMessage(), ex);
        } finally {
            // Ends transaction
            // If there was an error, the database won't be altered
            db.endTransaction();
        }
    }
}

them simply instantiate your helper with

MyDatabase myDb = new MyDatabase(getContext(),"databasename.db", null, 1);

The helper will then create the database, if it doesn't exist, upgrade it if an older version exists or simply open it if it exists and the version matches

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