Kotlin 和 Android 的“没有足够的信息来推断 T 参数”

将您的代码更改为此。发生主要更改的位置用星号标记。

package com.phenakit.tg.phenakit


import android.content.Context
import android.os.Bundle
import android.support.design.widget.BottomNavigationView
import android.support.v7.app.AppCompatActivity
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.BaseAdapter
import android.widget.ListView
import android.widget.TextView


public class MainActivity : AppCompatActivity() {


private var mTextMessage: TextView? = null


private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
when (item.itemId) {
R.id.navigation_home -> {
mTextMessage!!.setText(R.string.title_home)
return@OnNavigationItemSelectedListener true
}
R.id.navigation_dashboard -> {
mTextMessage!!.setText(R.string.title_dashboard)
return@OnNavigationItemSelectedListener true
}
R.id.navigation_notifications -> {
setContentView(R.layout.activity_list_view)
return@OnNavigationItemSelectedListener true
}
}
false
}


override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)


mTextMessage = findViewById(R.id.message) as TextView?
val navigation = findViewById(R.id.navigation) as BottomNavigationView
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener)




**val listView = findViewById<ListView>(R.id.list)**






**listView?.adapter = ListExampleAdapter(this)**
}


private class ListExampleAdapter(context: Context) : BaseAdapter() {
internal var sList = arrayOf("Eins", "Zwei", "Drei")
private  val mInflator: LayoutInflater


init {
this.mInflator = LayoutInflater.from(context)
}


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


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


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


override fun getView(position: Int, convertView: View?, parent: ViewGroup): View? {
val view: View?
val vh: ListRowHolder


if(convertView == null) {
view = this.mInflator.inflate(R.layout.list_row, parent, false)
vh = ListRowHolder(view)
view.tag = vh
} else {
view = convertView
vh = view.tag as ListRowHolder
}


vh.label.text = sList[position]
return view
}
}


private class ListRowHolder(row: View?) {
public var label: TextView


**init { this.label = row?.findViewById<TextView?>(R.id.label) as TextView }**
}
}

您必须使用 API 级别26(或更高)。这个版本改变了 View.findViewById()的签名-见这里的 https://developer.android.com/about/versions/oreo/android-8.0-changes#fvbi-signature

因此，在 findViewById的结果不明确的情况下，需要提供类型:

1/更改

val listView = findViewById(R.id.list) as ListView至

val listView = findViewById<ListView>(R.id.list)

2/更改

this.label = row?.findViewById(R.id.label) as TextView至

this.label = row?.findViewById<TextView>(R.id.label) as TextView

注意，在2/中只需要强制转换，因为 row是可空的 也可以为空，或者如果你使 row不为空，它就不会被要求。

改变 findViewById api

Public View findViewById (int id) ;

到

Public final T findViewById (int id)

所以，如果你是 API 26的目标，你可以改变

Val listView = findViewById (R.id.list)作为 ListView

到

Val listView = findViewById (R.id.list)

或者

Val listView: ListView = findViewById (R.id.list)

它的工作

    var et_user_name = findViewById(R.id.et_user_name) as EditText

    val et_user_name: EditText = findViewById(R.id.et_user_name)