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android-studiokotlintextview

Android Studio 4.1 Kotlin widget-ID not recognized in AminActivity.kt

I try to create a new project in Android Studio (AS) 4.1 with Kotlin. I use "empty activity" and create project "MyTest" .

AS creates activity_main.xml with unnamed TextView "Hello World". I give the id the name myText.

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/myText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

The created MainActivity.kt is standard and looks like this

package com.example.mytest

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle

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

All this is normal AS, BUT

now in MAinActivity.kt it should be possible to type

myText = "any string"

but here myText is not recognised. And I don't understand that.

I have some small test-projects from earlier AS version. They look identical - and it works to type myText and myText is immediatly recognized.

What is wrong with my coding or project creation! Having created several projects and compared with former projects, I see no fault with my doing. Who has an idea?

Solution

  • You need to integrate Kotlin Android Extensions in your project in order to you have your views recognized like that. Just add the following lines in your build.gradle:

    apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

    More info in this article: https://antonioleiva.com/kotlin-android-extensions/

    BUT

    synthetic will be deprecated in Kotlin 1.4.20, https://youtrack.jetbrains.com/issue/KT-42121 due to not being null-safe. If you are going to maintain the project you are building for a awhile it will be batter not to use Kotlin Android Extensions.

    Suggested alternatives in the link above are:

    • ViewBinding
    • FindViewById
    • Kotterknife (deprecated)
    • AndroidAnnotations

    FindViewById is the 'official' method and it's easy to use, Kotlin suggests ViewBinding which has some boilerplate as I read (I haven't used it yet).