ArrayAdapter使用Kotlin android

SoI正在学习kotlin，现在我需要编写一个ArrayAdapter，但我在try 这样做时出现了一些错误:

convertView = vi.inflate(resource, null) 

kotlin is telling me

Val cannot be reassigned

在站点kotline中，我将java类转换为kotlin类，并try 在该站点中这样做.为什么会出现错误？我该如何修复？这是全部代码.

open class MyAdapter(context: Context, resource: Int, list: ArrayList<MyItems>) :
        ArrayAdapter<MyItems>(context, resource, list) {

    var resource: Int
    var list: ArrayList<MyItems>
    var vi: LayoutInflater

    init {
        this.resource = resource
        this.list = list
        this.vi = context.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
    }


    override fun getView(position: Int, convertView: View?, parent: ViewGroup): View? {
        var holder: ViewHolder

        if(convertView == null){
            convertView = vi.inflate(resource, null) //error in this line
            holder = ViewHolder()

            holder.image = convertView.findViewById(R.id.myImage) as ImageView?

            convertView.tag(holder) //error in this line

        } else {
            holder = convertView.tag as ViewHolder
        }

        return convertView
    }

    internal class ViewHolder {
        var image: ImageView? = null
    }

}