类型不匹配：推断类型是 FragmentActivity？但上下文是预期的

Question

我想用 kotlin 在 tablayout 中插入菜单 gridview。我一直在 google 中搜索许多参考资料，但无济于事，在 adapter = FoodAdapter(this, foodsList) 中仍然出现 1 个错误。它说 "Type missmatch : inferred type as fragmentHome but Context was expected"。这是我 fragmentHome.kt

的代码

package com.example.ako.nextbrilliantgeneration

import android.os.Bundle
import android.support.v4.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.BaseAdapter
import android.content.Context
import android.support.v4.app.FragmentActivity
import kotlinx.android.synthetic.main.fragment_fragment_home.*
import kotlinx.android.synthetic.main.menu_entry.view.*

private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

class fragmentHome : Fragment() {


var adapter: FoodAdapter? = null
var foodsList = ArrayList<Menu>()


override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?


): View? {

    // Inflate the layout for this fragment
    return inflater.inflate(R.layout.fragment_fragment_home, container, false)

    foodsList.add(Menu("Coffee", R.drawable.profile))
    foodsList.add(Menu("Espersso", R.drawable.profile))
    foodsList.add(Menu("French Fires", R.drawable.profile))
    foodsList.add(Menu("Honey",R.drawable.profile))
    foodsList.add(Menu("Strawberry", R.drawable.profile))
    foodsList.add(Menu("Sugar cubes", R.drawable.profile))
    adapter = FoodAdapter(this, foodsList)

    gvFoods.adapter = adapter


}

class FoodAdapter : BaseAdapter {
    var foodsList = ArrayList<Menu>()
    var context: Context? = null


    constructor(context: Context, foodsList: ArrayList<Menu>) : super() {
        this.context = context
        this.foodsList = foodsList
    }

    override fun getCount(): Int {
        return foodsList.size
    }

    override fun getItem(position: Int): Any {
        return foodsList[position]
    }

    override fun getItemId(position: Int): Long {
        return position.toLong()
    }

    override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View {
        val food = this.foodsList[position]

        var inflator = context!!.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
        var foodView = inflator.inflate(R.layout.menu_entry, null)
        foodView.imgFood.setImageResource(food.image!!)
        foodView.tvName.text = food.name!!

        return foodView
    }
}

}

有什么解决办法吗？

谢谢

Answer 1

错误很明显，您尝试传递 this，它指的是 Fragment object，但您的适配器需要 Context，然后尝试传递 Activity，即 extends from Context.

替换此行

adapter = FoodAdapter(this, foodsList)

与

adapter = FoodAdapter(getActivity(), foodsList)

更新

calls to Java get and set methods that can be replaced with the use of Kotlin synthetic properties.

getActivity()  --> activity

Answer 2

您的适配器接收非空 Context，但您传入的是 Fragment。您可以尝试从片段中传入 activity，或者：

adapter = FoodAdapter(activity!!, foodsList)

或者如果您有最新的支持库：

adapter = FoodAdapter(requireActivity(), foodsList)

您收到无法访问的错误，因为您 return 太早离开方法，只需将其移至底部即可：

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
    foodsList.add(Menu("Coffee", R.drawable.profile))
    foodsList.add(Menu("Espersso", R.drawable.profile))
    foodsList.add(Menu("French Fires", R.drawable.profile))
    foodsList.add(Menu("Honey",R.drawable.profile))
    foodsList.add(Menu("Strawberry", R.drawable.profile))
    foodsList.add(Menu("Sugar cubes", R.drawable.profile))
    adapter = FoodAdapter(this, foodsList)

    gvFoods.adapter = adapter

    // move this line to last
    return inflater.inflate(R.layout.fragment_fragment_home, container, false)
}

Answer 3

这是一个很棒的更新，可以帮助使用 Kotlin 编写代码的开发人员。 getActivity 方法已用 @Nullable 注释，以更好地支持 Kotlin 空安全。以前，此方法可能 return null，因此会在 Kotlin 代码中导致 IllegalStateException，因为在需要非 null 类型的地方会使用 null 对象。

为了最好地处理用 @Nullable 注释的方法的这些情况，请使用 let 运算符将可空对象解包为非空对象。

getActivity()?.let { adapter = FoodAdapter(it, foodList) }

不要将 requireActivity() 用于 "ensure" 非空 activity，因为如果您的 activity 确实为空，此方法将抛出异常。

Answer 4

在 Fragment class 中你应该使用以下方式：

mFargmentSettingBinding.txtAppVersionCode.setText(Static.getAppVersion(activity!!))

类型不匹配：推断类型是 FragmentActivity？但上下文是预期的

Type mismatch: inferred type is FragmentActivity? but Context was expected

android

android-studio

kotlin-android-extensions