“没有足够的信息来推断参数T".与Kotlin和Android [英] "Not enough information to infer parameter T" with Kotlin and Android
问题描述
我正在尝试使用Kotlin在Android应用中复制以下ListView: https://github.com/bidrohi/KotlinListView .
I'm trying to replicate the following ListView in my Android app using Kotlin: https://github.com/bidrohi/KotlinListView.
不幸的是,我遇到一个错误,无法解决自己. 这是我的代码:
Unfortunately I'm getting an error I'm unable to resolve myself. Here's my code:
MainActivity.kt:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val listView = findViewById(R.id.list) as ListView
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 val label: TextView
init {
this.label = row?.findViewById(R.id.label) as TextView
}
}
}
布局与此处完全相同: https://github.com/bidrohi/KotlinListView/tree/master/app/src/main/res/layout
The layouts are exactly as here: https://github.com/bidrohi/KotlinListView/tree/master/app/src/main/res/layout
我得到的完整错误消息是: 错误:(92,31)类型推断失败:没有足够的信息来有趣地推断参数T findViewById(p0:Int):T! 请明确指定.
The full error message I'm getting is this: Error:(92, 31) Type inference failed: Not enough information to infer parameter T in fun findViewById(p0: Int): T! Please specify it explicitly.
我将很高兴能获得任何帮助.
I'd appreciate any help I can get.
推荐答案
您必须使用API级别26(或更高).此版本已更改View.findViewById()
的签名-参见此处 https://developer.android.com/about/versions/oreo/android-8.0-changes#fvbi-signature
You must be using API level 26 (or above). This version has changed the signature of View.findViewById()
- see here https://developer.android.com/about/versions/oreo/android-8.0-changes#fvbi-signature
因此,在您的情况下,如果findViewById
的结果不明确,则需要提供以下类型:
So in your case, where the result of findViewById
is ambiguous, you need to supply the type:
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
请注意,在2/中,仅强制转换,因为row
可为空.如果label
也可以为空,或者如果您将row
设为不可为空,则不需要.
Note that in 2/ the cast is only required because row
is nullable. If label
was nullable too, or if you made row
not nullable, it wouldn't be required.
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