Android/Kotlin：如何创建使用DBLocal类的类？错误消息：类型不匹配需要上下文

我想创建一个通用的DB类来管理一个本地DB和另一个DB。我有一个错误，但我不明白是什么问题

普通课程：

class DBHandler {
    companion object {
        val sharedInstance = DBHandler() //gérer si sharedinstance est null pour éviter pb d'ecriture
    }

    fun methodToSelectData(strQuery: String, dataBase: String)/*, completion: @escaping (_ result:*/
    {
        print(message = strQuery)

        val dbLocal = DBLocal(this, null, null, 1) //pb on this line
        dbLocal.methodToSelectData(strQuery)
    }
}

class DBLocal(context: Context, name: String?, factory: SQLiteDatabase.CursorFactory?, version: Int) : SQLiteOpenHelper(context, DATABASE_NAME, factory, DATABASE_VERSION)
{

    override fun onCreate(db: SQLiteDatabase)
    {
        print(DATABASE_NAME)
    }

    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int)
    {

    }
    fun methodToSelectData(strQuery: String)/*, completion: @escaping (_ result:*/
    {

    }

    fun methodToInsertUpdateDeleteData(strQuery: String)/*, completion: @escaping (_ result: Bool) -> Void)*/
    {

    }
    companion object {
        private val DATABASE_VERSION = 1
        private val DATABASE_NAME = "Local.db"
    }
}

DB类：

class DBHandler {
    companion object {
        val sharedInstance = DBHandler() //gérer si sharedinstance est null pour éviter pb d'ecriture
    }

    fun methodToSelectData(strQuery: String, dataBase: String)/*, completion: @escaping (_ result:*/
    {
        print(message = strQuery)

        val dbLocal = DBLocal(this, null, null, 1) //pb on this line
        dbLocal.methodToSelectData(strQuery)
    }
}

class DBLocal(context: Context, name: String?, factory: SQLiteDatabase.CursorFactory?, version: Int) : SQLiteOpenHelper(context, DATABASE_NAME, factory, DATABASE_VERSION)
{

    override fun onCreate(db: SQLiteDatabase)
    {
        print(DATABASE_NAME)
    }

    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int)
    {

    }
    fun methodToSelectData(strQuery: String)/*, completion: @escaping (_ result:*/
    {

    }

    fun methodToInsertUpdateDeleteData(strQuery: String)/*, completion: @escaping (_ result: Bool) -> Void)*/
    {

    }
    companion object {
        private val DATABASE_VERSION = 1
        private val DATABASE_NAME = "Local.db"
    }
}

---

提前感谢。

您可以为

methodToSelectData

fun methodToSelectData(context : Context, strQuery: String, dataBase: String)/*, completion: @escaping (_ result:*/
{
    print(message = strQuery)

    val dbLocal = DBLocal(context, null, null, 1) //pb on this line
    dbLocal.methodToSelectData(strQuery)
}

问题：DBLocal类接收一个上下文作为第一个参数，但是当您从DBHandler类调用它时

val dbLocal = DBLocal(this, null, null, 1) //pb on this line

您将

此

作为DBLocal类传递，该类不是Context类的子类的上下文。这就是你的应用程序抛出错误的原因

错误消息：类型不匹配需要上下文

解决方案：简单的解决方案是将上下文传递到需要上下文来执行作业的方法中

fun methodToSelectData(context: Context, strQuery: String, dataBase: String)/*, completion: @escaping (_ result:*/ {
    print(message = strQuery)

    val dbLocal = DBLocal(context, null, null, 1) //pb on this line
    dbLocal.methodToSelectData(strQuery)
}

并在调用DBHandler时传递上下文，例如在活动或服务中

DBHandler.sharedInstance.methodToSelectData(this, "your query", "dataBase")

---

您在哪里使用

methodToSelectData

方法？在活动/片段中？