Kotlin类型不匹配：推断类型是View！ 但TextView是预料之中的

Question

Good day! Using Kotlin 1.1.51 in Android Studio 3.0 , targeting Android API 26 to create RecyclerView with next ViewHolder , but receiving error on building the project:

Type mismatch: inferred type is View! but TextView was expected

So I can't find TextView directly to ViewHolder variable, but found around way - find View and after that cast with as TextView as you can see in the code for holder. textView. Doesn't look so good, so are there solutions how to prevent this error or is it a bug? The code of RecyclerView .Adapter:

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VH {
        val view = LayoutInflater.from(parent.context)
                .inflate(R.layout.custom_item_view, parent, false)
        return VH(view)
    }

    override fun onBindViewHolder(holder: VH, position: Int) {
        val event: TimelineEvent = items[position]

        // does not work because of error in VH class
        holder.timeView.text = event.time

        // works
        (holder.textView as TextView).text = event.text
    }

    class VH(itemView: View) : RecyclerView.ViewHolder(itemView) {
        // error: Type mismatch: inferred type is View! but TextView was expected
        val timeView: TextView = itemView.findViewById(R.id.timeline_item_time)

        // works fine
        val textView: View = itemView.findViewById(R.id.timeline_item_text)
    }

Answer 1

It seems like you're not on API level 26 or newer yet. That's when findViewById was changed so that it returns a generic T instead of the base View class, which enables you to use it from Kotlin in these ways .

You can either manually cast the result of the findViewById call as @AlexTa suggested in the other answer , or you can update your support library version to 26 or later - the latest currently is 27.0.0 . These new versions are available from Google's Maven repository .

Answer 2

You just need to cast found view as expected type, to do so:

val timeView: TextView = itemView.findViewById(R.id.timeline_item_time) as TextView

or

val timeView: TextView = itemView.findViewById<TextView>(R.id.timeline_item_time)