CODEWITHSUNDEEP
androidkotlinandroid-8.0-oreo
Timo Güntner
Timo Güntner

Reputation: 2861

"Not enough information to infer parameter T" with Kotlin and Android

I'm trying to replicate the following ListView in my Android app using Kotlin: https://github.com/bidrohi/KotlinListView.

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
    }
}
}

The layouts are exactly as here: https://github.com/bidrohi/KotlinListView/tree/master/app/src/main/res/layout

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.

I'd appreciate any help I can get.

Upvotes: 151

Views: 142913

Answers (7)

Dorababu Arigi
Dorababu Arigi

Reputation: 11

I came across this error while using the DataBindingUtil.setContentView(this,R.layout.activity_main)

The error came here because this is supposed to return the binding associated with the layout_main(inflatted layout) so I resolved this error by :

ActivityMainBinding binding = DataBindingUtil.setContentView(this,R.layout.activity_main)

So, your error may be mostly with handling the return value.Try to set that and check.

Upvotes: 0

Azade Rahmati
Azade Rahmati

Reputation: 207

In android 12 remove as from your code and put your model in <> in front of getParcelableExtra.

change

intent.getParcelableExtra("MyModel") as MyModel

to

intent.getParcelableExtra `<MyModel>` ("MyModel")!!

Upvotes: 1

nmw
nmw

Reputation: 6764

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

So in your case, where the result of findViewById is ambiguous, you need to supply the type:

1/ Change

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

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

2/ Change

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

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

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.

Upvotes: 269

pauminku
pauminku

Reputation: 3596

I would suggest you to use synthetics kotlin Android extension:

https://kotlinlang.org/docs/tutorials/android-plugin.html

https://antonioleiva.com/kotlin-android-extensions/

In your case the code will be something like this:

init {
   this.label = row.label
}

As simple as that ;)

Upvotes: 1

Keshav Gera
Keshav Gera

Reputation: 11244

Its Working

API Level 25 or below use this 

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

API Level 26 or Above use this 

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

Happy Coding !

Upvotes: 8

Trinea
Trinea

Reputation: 669

Andoid O change findViewById api from

public View findViewById(int id);

to

public final T findViewById(int id)

so, if you are target to API 26, you can change

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

to

val listView = findViewById(R.id.list)

or

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

Upvotes: 9

Alf Moh
Alf Moh

Reputation: 7427

Change your code to this. Where the main changes occurred are marked with asterisks.

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 }**
    }
}

Upvotes: 4

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