Kotlin-Android First App Unresolved Reference TextView Button etc

Question

I'm new to Android & Kotlin development.

I wanted to get started with a simple "Hello World", but am already running into problems.

I added a Textview to my MainActivity and want to set an onClick listener to change the text of a TextView I dragged into the activity.

The compiler is now complaining that 'TextView' is an unresolved reference (it does the same with Buttons etc.).

I then added a kotlinx import as suggested by a website, but this fails to solve anything. Code sample below, anything with an asterisk as a line comment was added by me.

package com.example.my.mynewapp

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.fragmentX.view.* // *

class MainActivity : AppCompatActivity() {

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

        val textView: TextView = findViewById(R.id.testView) as TextView  // *
        textView.setOnClickListener { // *
            textView.text = "You clicked me! You flipping clicked me!" // *
        } // *

    }
}

Would anyone have any idea what's going on?

Answer 1

It should have been automatically imported, but there should be

import android.widget.<WhateverIsMissing>

Replace WhateverIsMissing with the reference that is unresolved

Answer 2

if you use Android Studio v.4.2.1 you have to add this line in (build.gradle) file like this:-

id 'kotlin-android-extensions'

Answer 3

You are inflating activity_main.xml in your class.
Does this TextView belong to the above layout?
If it does then you don't need findViewById()
Just add to your imports:

import kotlinx.android.synthetic.main.activity_main.*

and not:

import kotlinx.android.synthetic.main.fragmentX.view.*

then use testView (this is the id of the TextView unless it's a typo) anywhere in your activity class.