Myujth

I'm using androidx navigation architecture along with Kotlin 1.2.71 in Android studio 3.2.1. My fragment code is:

package com.dell.andnav.fragments

import android.os.Bundle
import android.support.v4.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import androidx.navigation.fragment.findNavController
import com.dell.andnav.R
import kotlinx.android.synthetic.main.fragment_welcome.*


/**
 * A simple [Fragment] subclass.
 * Use the [WelcomeFragment.newInstance] factory method to
 * create an instance of this fragment.
 *
 */
class WelcomeFragment : Fragment() 

 override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
 savedInstanceState: Bundle?): View? 
 // Inflate the layout for this fragment
 return inflater.inflate(R.layout.fragment_welcome, container, false)
 

 override fun onViewCreated(view: View, savedInstanceState: Bundle?) 
 super.onViewCreated(view, savedInstanceState)
 detailButton.setOnClickListener 
 findNavController().navigate(R.id.action_welcomeFragment_to_detailsFragment)
 
 

 companion object 
 @JvmStatic
 fun newInstance() = WelcomeFragment()
 
 

And layout code is:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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:id="@+id/frameLayout"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context=".fragments.WelcomeFragment">


 <Button
 android:id="@+id/detailButton"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="@string/to_detail_fragment"
 app:layout_constraintBottom_toBottomOf="parent"
 app:layout_constraintLeft_toLeftOf="parent"
 app:layout_constraintRight_toRightOf="parent"
 app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout> 

My build.gradle is:

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
apply plugin: 'androidx.navigation.safeargs'

android 
 compileSdkVersion 28
 defaultConfig 
 applicationId "com.dell.andnav"
 minSdkVersion 21
 targetSdkVersion 28
 versionCode 1
 versionName "1.0"
 testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
 androidExtensions 
 experimental = true
 
 
 buildTypes 
 release 
 minifyEnabled false
 proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
 
 


dependencies 
 def nav_version = "1.0.0-alpha07"
 implementation fileTree(dir: 'libs', include: ['*.jar'])
// implementation 'com.android.support:appcompat-v7:28.0.0'
 implementation 'com.android.support.constraint:constraint-layout:1.1.3'
// implementation 'com.android.support:support-v4:28.0.0'
 testImplementation 'junit:junit:4.12'
 androidTestImplementation 'com.android.support.test:runner:1.0.2'
 androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

 implementation 'androidx.lifecycle:lifecycle-extensions:2.0.0'
 implementation 'androidx.legacy:legacy-support-v4:1.0.0'
 implementation 'androidx.multidex:multidex:2.0.0'
 implementation 'androidx.appcompat:appcompat:1.0.2'

 implementation "android.arch.navigation:navigation-fragment-ktx:$nav_version"
 implementation "android.arch.navigation:navigation-ui-ktx:$nav_version"

 implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"

repositories 
 mavenCentral()

When I try to run my code, I get below error:

Unresolved reference. None of the following candidates is applicable because of receiver type mismatch:
public val Activity.detailButton: Button! defined in kotlinx.android.synthetic.main.fragment_welcome
public val Dialog.detailButton: Button! defined in kotlinx.android.synthetic.main.fragment_welcome
public val android.app.Fragment.detailButton: Button! defined in kotlinx.android.synthetic.main.fragment_welcome
public val androidx.fragment.app.Fragment.detailButton: Button! defined in kotlinx.android.synthetic.main.fragment_welcome
public val LayoutContainer.detailButton: Button! defined in kotlinx.android.synthetic.main.fragment_welcome

How can I resolve that error?

Button you are accessing is inside your fragement but your are accessing it directly. You should access it via parent view like we do with java rootview.findViewById() so use

view.detailButton.setOnClickListener 
 findNavController().navigate(R.id.action_welcomeFragment_to_detailsFragment)

In my case this function led to the error:

private fun showProgress(view: View? = null) 
 (view?.progressBar ?: progressBar)?.visibility = View.VISIBLE

Android Studio offered layouts that contained progressBar, and I chose one. But view?.progressBar continued to be red. Then I shortened a header:

private fun showProgress(view: View).

Only after that AS offered layouts. Then I again wrote: private fun showProgress(view: View? = null).