Question

在Kotlin尝试编写Android项目时，有一个问题令人困惑。

当我尝试调用一些基本的Android库函数时，编译器会要求非常具体的引用。这是一个初始化LoaderManager的示例。记下最后一个参数。

  override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        loaderManager.initLoader(LOADER_ROUTINE, arguments, this as android.support.v4.app.LoaderManager.LoaderCallbacks<Cursor>)
   }

这是奇怪的部分。如果我创建一个基于Java的Fragment，在没有详细程度或编译器错误的情况下初始化加载器，然后转换为Kotlin，则没有错误：

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    loaderManager.initLoader(88, arguments, this)

}

我错过了什么。 Kotlin需要在什么上下文中阻止必须在第一个示例中添加 as WhateverSpecificClass 的解决方法？

编辑：这是一些额外的背景。编译期间的具体错误是：

    Type inference failed: 

fun <D : Any!> initLoader
(id: Int,
 args: Bundle!,
 callback: LoaderManager.LoaderCallbacks<D!>!)
: Loader<D!>!
cannot be applied Int,
Bundle!,
EditRoutine
)

Fragment的整个包装代码

    package com.inviscidlabs.ero.Fragments

import android.app.LoaderManager
import android.content.ContentValues
import android.content.Context
import android.content.CursorLoader
import android.content.Loader
import android.database.Cursor
import android.os.Bundle
import android.support.design.widget.TextInputEditText
import android.support.v4.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import butterknife.BindView
import butterknife.ButterKnife
import com.inviscidlabs.ero.Data.EroProvider
import com.inviscidlabs.ero.Data.Keys
import com.inviscidlabs.ero.Data.Routine
import com.inviscidlabs.ero.R



    class EditRoutine : Fragment(),  LoaderManager.LoaderCallbacks<Cursor>{

    //Values
    private val LOADER_ROUTINE: Int = 9150

    //Vars
    private var mRoutineID: String? = null

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)


        //If the routineID passed is a legitimate ID, initialize the loader
        if(!mRoutineID.equals(Keys.m_NullValue)){
            // this would not work: loaderManager.initLoader(LOADER_ROUTINE, arguments, this)
        loaderManager.initLoader(LOADER_ROUTINE, arguments, this as android.support.v4.app.LoaderManager.LoaderCallbacks<Cursor>)

        }
    }

    //Loader Functions


    override fun onCreateLoader(id: Int, args: Bundle): Loader<Cursor>? {
        if(id==LOADER_ROUTINE){

            val projection = arrayOf(Routine.Table._ID, Routine.Table.KEY_NAME)

            val selection = Routine.Table._ID + "=?"
            val selectionArgs = arrayOf(args.getString(Keys.b_RoutineID))

            val cL = CursorLoader(activity, //Context
                    EroProvider.CONTENT_URI_WORKOUT, //URI
                    projection, //The fields we want (must include ID
                    selection, //WHERE statement for SQL
                    selectionArgs, null)//Arguments for WHERE
            return cL
        }
        return  null
    }

    override fun onLoaderReset(loader: Loader<Cursor>?) {

    }

    override fun onLoadFinished(loader: Loader<Cursor>?, data: Cursor?) {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }

}

Answer 1

上下文参数将简单地从LoaderCallbacks接口使用，因此您将导入其语句并将其作为类签名的一部分实现，如下所示：

import android.os.Bundle
import android.support.v4.app.Fragment
import android.support.v4.app.LoaderManager
import android.support.v4.content.Loader
import android.database.Cursor

class WorkSpaceActivity : Fragment(), LoaderManager.LoaderCallbacks<Cursor> {

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)

        loaderManager.initLoader(88, null, this)
    }

    override fun onCreateLoader(id: Int, args: Bundle?): Loader<Cursor> {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }

    override fun onLoadFinished(loader: Loader<Cursor>?, data: Cursor?) {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }

    override fun onLoaderReset(loader: Loader<Cursor>?) {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }
}

除非明确引用，否则Kotlin无法识别参数

1 个答案: