    apply plugin: &#39;kotlin-android-extensions&#39;.
When i add this extensions in android studio preview, give me this error
&quot;Error:(1, 0) Plugin with id &#39;kotlin-android-extensions&#39; not found.&quot;.

My build gradle

  

 

       apply plugin: &#39;com.android.application&#39;
    
    android {
        compileSdkVersion 26
        buildToolsVersion &quot;26.0.1&quot;
        defaultConfig {
            applicationId &quot;com.example.mohamed_elbaz.myapplication&quot;
            minSdkVersion 15
            targetSdkVersion 26
            versionCode 1
            versionName &quot;1.0&quot;
            testInstrumentationRunner &quot;android.support.test.runner.AndroidJUnitRunner&quot;
        }
        buildTypes {
            release {
                minifyEnabled false
                proguardFiles getDefaultProguardFile(&#39;proguard-android.txt&#39;), &#39;proguard-rules.pro&#39;
            }
        }
    }
    
    dependencies {
        implementation fileTree(dir: &#39;libs&#39;, include: [&#39;*.jar&#39;])
        implementation &#39;com.android.support:appcompat-v7:26.0.2&#39;
        implementation &#39;com.android.support.constraint:constraint-layout:1.0.2&#39;
        testImplementation &#39;junit:junit:4.12&#39;
        androidTestImplementation &#39;com.android.support.test:runner:1.0.1&#39;
        androidTestImplementation &#39;com.android.support.test.espresso:espresso-core:3.0.1&#39;
    }





Error:(1, 0) Plugin with id &#39;kotlin-android-extensions&#39; not found

I want to initialize ViewModel in Activity using androidx library

I have tried what documentation says but it is not working. the &quot;.of&quot; is not resolved.
 

```kotlin
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.ViewModelProvider
import com.example.myapplication.databinding.ActivityMainBinding`

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val binding: ActivityMainBinding = DataBindingUtil.setContentView(
            this, R.layout.activity_main)
        binding.setLifecycleOwner(this)

        var model = ViewModelProvider.of(this).get(SheduleViewModel::class.java)

    }
}
```



of is not resolved, maybe there are another way to do it in androidx



how to instantiate ViewModel In AndroidX?

How to use Kotlin Android Extensions with `Fragment`s?
If I use them inside `onCreateView()`, I get this `NullPointerException` exception: 

&gt; Caused by: java.lang.NullPointerException: Attempt to invoke virtual
&gt; method &#39;android.view.View android.view.View.findViewById(int)&#39; on a
&gt; null object reference

Here is the fragment code: 

    package com.obaied.testrun.Fragment
    
    import android.os.Bundle
    import android.support.v4.app.Fragment
    import android.util.Log
    import android.view.LayoutInflater
    import android.view.View
    import android.view.ViewGroup
    import com.obaied.acaan.R
    import kotlinx.android.synthetic.main.fragment_card_selector.*
    
    public class CardSelectorFragment : Fragment() {
        val TAG = javaClass.canonicalName
    
        companion object {
            fun newInstance(): CardSelectorFragment {
                return CardSelectorFragment()
            }
        }
    
        override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
            var rootView = inflater?.inflate(R.layout.fragment_card_selector, container, false)
            btn_K.setOnClickListener { Log.d(TAG, &quot;onViewCreated(): hello world&quot;); }
    
            return rootView
        }
    }
    `

NullPointerException when trying to access views in a Kotlin fragment

I&#39;m trying to rebuild my Android Studio Gradle project (containing mostly Kotlin code), but it started to throw an `UnableToDeleteFileException` during the cleaning/rebuilding process:

    Execution failed for task &#39;:app:clean&#39;.
    &gt; Unable to delete file: C:\Users\User\KotlinGameEngine\app\build\intermediates\exploded-aar\com.android.support\appcompat-v7\23.0.1\jars\classes.jar

This started happening after I tried to change my project&#39;s package structure. Unfortunately, I did it by renaming and moving the source folders rather than refactoring through Android Studio, which was a bad idea.

I&#39;ve been searching for a solution to this problem all day, and these are the things I have tried to no avail:

- Doing a Gradle sync;
- Reinstalling Java JRE and Java SDK;
- Reinstalling the latest version of Android Studio (1.4);
- Rolling back to the previous AS version (1.3);
- Invalidating the AS cache and restarting;
- Deleting the `gradle` and `.gradle` directories in the project directory;
- Deleting the `.gradle` directory in my user directory;
- Running `gradlew clean` from the AS terminal;
- Manually copying the sources over to a new project (weird that it somehow persists across projects...)

Things that I&#39;ve tried with a little success, but only let me perform one more clean and rebuild before the error occurs again:

- Closing AS, manually deleting the build files, and opening it again;
- Killing the `java.exe` process while AS is running (this could technically be done every time, but it&#39;s tedious and slows down the build process)

So it seems that compile the Java process may put a lock on the build files for some reason, but it might also be something to do with Kotlin. I have a (more mature) Java Android project that I&#39;m working on, though I can&#39;t reproduce this error when cleaning it. It seems to only happen to my Kotlin project.



Update:
-
I&#39;ve found that the problem is being caused by the Kotlin Android plugin. The problem disappears when I remove `apply plugin: &#39;kotlin-android&#39;` from the module&#39;s `build.gradle` file and comes back when I reinsert it. Feel free to offer any insight into this.

Update 2:
-
The last update isn&#39;t the cause. I found that if a project contains a Kotlin file then rebuilding and cleaning fails. It continues to fail, even if all the Kotlin files are removed, until the background Java process is killed, meaning it has some kind of lock on the build files. I submitted a bug here with more details and steps to reproduce the bug: [KT-9440][1]


  [1]: https://youtrack.jetbrains.com/issue/KT-9440 &quot;KT-9440&quot;

Error: Execution failed for task &#39;:app:clean&#39;. Unable to delete file

After downloaded and installed latest Kotlin plugin I have **Outdated Kotlin Runtime** warning from Android Studio that telling me:

&gt; Your version of Kotlin runtime in &#39;kotlin-stdlib-1.1.2&#39; library is
&gt; 1.1.2, while plugin version is 1.1.2-release-Studio2.3-3. Runtime library should be updated to avoid compatibility problems.

I tried to click *Update Runtime* button but getting another message:

&gt; Automatic library version update for Gradle projects is currently
&gt; unsupported. Please update your build.gradle manually.

How to solve this issue?

Outdated Kotlin Runtime warning in Android Studio

I am trying to try out Kotlin and the Kotlin Android extensions in Android Studio.  I have tried this both in Android Studio v 1.5.1 on Ubuntu 14.04, and in Android Studio v 1.5.1 on OS X El Capitan with the same result.

Here is what I am doing:

1. I install the Kotlin plugin 1.0.0-beta-35950-IJ141-11
2. Create a new blank Android project
3. Convert the MainActivity file to Kotlin (via help-&gt;findaction-&gt;convert file to kotlin) 
4. Configure the project for Kotlin

I then go into the generated content_main.xml file and add an id (hello) for the &quot;Hello World!&quot; TextView.

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
    &lt;RelativeLayout xmlns:android=&quot;http://schemas.android.com/apk/res/android&quot;
        xmlns:app=&quot;http://schemas.android.com/apk/res-auto&quot;
        xmlns:tools=&quot;http://schemas.android.com/tools&quot;
        android:layout_width=&quot;match_parent&quot;
        android:layout_height=&quot;match_parent&quot;
        android:paddingBottom=&quot;@dimen/activity_vertical_margin&quot;
        android:paddingLeft=&quot;@dimen/activity_horizontal_margin&quot;
        android:paddingRight=&quot;@dimen/activity_horizontal_margin&quot;
        android:paddingTop=&quot;@dimen/activity_vertical_margin&quot;
        app:layout_behavior=&quot;@string/appbar_scrolling_view_behavior&quot;
        tools:context=&quot;com.gmail.npnster.mykotlinfirstproject.MainActivity&quot;
        tools:showIn=&quot;@layout/activity_main&quot;&gt;
    
        &lt;TextView
            android:layout_width=&quot;wrap_content&quot;
            android:layout_height=&quot;wrap_content&quot;
            android:text=&quot;Hello World!&quot;
            android:id=&quot;@+id/hello&quot;
            /&gt;
    &lt;/RelativeLayout&gt;  

Then in the converted MainActivity I add a line to set the TextView. (shown below).
Android Studio then prompts me (via alt-enter) to insert this line (also shown below)

    import kotlinx.android.synthetic.main.content_main.*

So at this point everything _seems_ fine

but then when I try to compile this I get 

    Unresolved reference: kotlinx
    Unresolved reference: kotlinx
    Unresolved reference: hello

Notice that I did **not** install the Kotlin Android extensions plugin.  As of a couple of days ago this is now supposed to be included in the main plug in and is marked as obsolete.  (In fact if you try to install it when you have the latest plugin, nothing new is installed) 

Anyone see what I am doing wrong?

MainActivity

    import android.os.Bundle
    import android.support.design.widget.FloatingActionButton
    import android.support.design.widget.Snackbar
    import android.support.v7.app.AppCompatActivity
    import android.support.v7.widget.Toolbar
    import android.view.View
    import android.view.Menu
    import android.view.MenuItem
    import kotlinx.android.synthetic.main.content_main.*
    
    
    class MainActivity : AppCompatActivity() {
    
        override fun onCreate(savedInstanceState: Bundle?) {
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
            val toolbar = findViewById(R.id.toolbar) as Toolbar
            setSupportActionBar(toolbar)
            print(&quot;setting text view value to hey&quot;)
            hello.text = &quot;hey&quot;
    
            val fab = findViewById(R.id.fab) as FloatingActionButton
            fab.setOnClickListener { view -&gt; Snackbar.make(view, &quot;Replace this with your own action&quot;, Snackbar.LENGTH_LONG).setAction(&quot;Action&quot;, null).show() }
        }
    
        override fun onCreateOptionsMenu(menu: Menu): Boolean {
            // Inflate the menu; this adds items to the action bar if it is present.
            menuInflater.inflate(R.menu.menu_main, menu)
            return true
        }
    
        override fun onOptionsItemSelected(item: MenuItem): Boolean {
            // Handle action bar item clicks here. The action bar will
            // automatically handle clicks on the Home/Up button, so long
            // as you specify a parent activity in AndroidManifest.xml.
            val id = item.itemId
    
            //noinspection SimplifiableIfStatement
            if (id == R.id.action_settings) {
                return true
            }
    
            return super.onOptionsItemSelected(item)
        }
    }

Unresolved reference: kotlinx

How to add an item to an `ArrayList` in Kotlin?

How to add an item to an ArrayList in Kotlin?

As a Java developer, the concept of a backing field is a bit foreign to me. Given:
```
class Sample {
    var counter = 0 // the initializer value is written directly to the backing field
    set(value) {
        if (value &gt;= 0) field = value
    }
}
```
What&#39;s this backing field good for? [Kotlin docs](https://kotlinlang.org/docs/reference/properties.html) said: 
&gt;*Classes in Kotlin cannot have fields. However, sometimes it is necessary to have a backing field when using custom accessors*. 

Why? What&#39;s the difference with using the properties name itself inside the setter, eg.* 
```   
class Sample {        
    var counter = 0
    set(value) {
        if (value &gt;= 0) this.counter = value // or just counter = value?
    }
}
```

What&#39;s Kotlin Backing Field For?

I am working with Single viewModel for the Activity and all of it&#39;s fragment.

So to initialise `viewmodel` if have to write this setup code in `onActivityCreated` of all the fragment&#39;s

        override fun onActivityCreated(savedInstanceState: Bundle?) {
            super.onActivityCreated(savedInstanceState)
            viewModel = ViewModelProviders.of(activity!!).get(NoteViewModel::class.java)
        }

I was going thorough the Android KTX extension page:([refer here][1]) 

and i found i can initialise view model like this:

        // Get a reference to the ViewModel scoped to this Fragment
        val viewModel by viewModels&lt;MyViewModel&gt;()
    
        // Get a reference to the ViewModel scoped to its Activity
        val viewModel by activityViewModels&lt;MyViewModel&gt;()

So I added below dependency&#39;s to my gradle(app):

        //ktx android
        implementation &#39;androidx.core:core-ktx:1.0.2&#39;
        implementation &#39;androidx.fragment:fragment-ktx:1.0.0&#39;
        implementation &quot;androidx.lifecycle:lifecycle-extensions:2.0.0&quot;

But when i try to use `viewModels/activityViewModels` in my application their reference in not found.
  
I want help in how to use these extension&#39;s with some basic example i tried searching for examples haven&#39;t found any.

  [1]: https://developer.android.com/kotlin/ktx#fragment

how to get viewModel by viewModels? (fragment-ktx)

How does the new [ViewBinding][1] compare with the [Kotlin Android Extensions][2] with synthetic views bindings?

Apart from the NullSafety and TypeSafety provided by new ViewBindings, why should we consider ditching the Kotlin way of using synthetic bindings on Views?

Is the new ViewBinding more performant since it generates the Binding class beforehand?


  [1]: https://developer.android.com/topic/libraries/view-binding
  [2]: https://kotlinlang.org/docs/tutorials/android-plugin.html

ViewBinding vs Kotlin Android Extensions with synthetic views

I&#39;m getting error in Kotlin in this part:

```
class GitHubRepoAdapter(
    private val context: Context,
    private val values: List&lt;GithubRepo&gt;
) : ArrayAdapter&lt;GithubRepo&gt;(
    context, 
    R.layout.list_item,
    values
)
```

`private val context: Context` 


In the log it says:

&gt; ```
&gt; Error:(14, 25) Accidental override: The following declarations have the same JVM signature
&gt;(getContext()Landroid/content/Context;):  
&gt;     fun &lt;get-context&gt;(): Context  
&gt;     fun getContext(): Context!
&gt; ```

I&#39;m not able to see what is causing the problem.

Accidental override: The following declarations have the same JVM signature

I am new in kotlin. I have found and tried to use synthetic method instead of annoying method `findViewById` in my `Activity` class, but I have found &quot;If we want to call the synthetic properties on View (useful in adapter classes), we should also import kotlinx.android.synthetic.main.view.*.&quot; But I can&#39;t figure out how it exactly works? Is there any examples?

Kotlin synthetic in Adapter or ViewHolder

I&#39;m trying to add an element list to the list of string, but I found `Kotlin` does not have an add function like `java` so please help me out how to add the items to the list. 

	class RetrofitKotlin : AppCompatActivity() {

		var listofVechile:List&lt;Message&gt;?=null
		var listofVechileName:List&lt;String&gt;?=null
		var listview:ListView?=null
		var progressBar:ProgressBar?=null
		override fun onCreate(savedInstanceState: Bundle?) {
			super.onCreate(savedInstanceState)
			setContentView(R.layout.activity_retrofit_kotlin)

			listview=findViewById&lt;ListView&gt;(R.id.mlist)
			var apiInterfacee=ApiClass.client.create(ApiInterfacee::class.java)
			val call=apiInterfacee.getTaxiType()
			call.enqueue(object : Callback&lt;TaxiTypeResponse&gt; {

				override fun onResponse(call: Call&lt;TaxiTypeResponse&gt;, response: Response&lt;TaxiTypeResponse&gt;) {

					listofVechile=response.body()?.message!!
					println(&quot;Sixze is here listofVechile   ${listofVechile!!.size}&quot;)
					if (listofVechile!=null) {
						for (i in 0..listofVechile!!.size-1) {

							//how to add the name only listofVechileName list

						}
					}
					//println(&quot;Sixze is here ${listofVechileName!!.size}&quot;)
					val arrayadapter=ArrayAdapter&lt;String&gt;(this@RetrofitKotlin,android.R.layout.simple_expandable_list_item_1,listofVechileName)
					listview!!.adapter=arrayadapter

				}
				override fun onFailure(call: Call&lt;TaxiTypeResponse&gt;, t: Throwable) {
				 
				}
			})
		}
	}

How to add an item to a list in Kotlin?

I have created a Kotlin Activity, but I am not able to extend the activity. I am getting this message: `This type is final, so it cannot be inherited from`. How to remove `final` from Kotlin&#39;s activity, so it can be extended?

Kotlin Activity cannot be extended. This type is final, so it cannot be inherited

    fun launchNextScreen(context: Context, people: People): Intent {
        val intent = Intent(context, NextScreenActivity::class.java)
        intent.putExtra(EXTRA_PEOPLE, (Parcelable) people)
        //intent.putExtra(EXTRA_PEOPLE, people as Parcelable)
        //intent.putExtra(EXTRA_PEOPLE, people)
        // tried above all three ways
        return intent
    }

I tried the above code to pass an instance of the `People` class via intent using kotlin, but I am getting an error.
What am I doing wrong?

How to Pass custom object via intent in kotlin

I am trying to remove all non alphanumeric characters from a string.

I tried using `replace()` with a regex as followed:

    var answer = answerEditText.text.toString()
    Log.d(&quot;debug&quot;, answer)
    answer = answer.replace(&quot;[^A-Za-z0-9 ]&quot;, &quot;&quot;).toLowerCase()
    Log.d(&quot;debug&quot;, answer)

&gt;D/debug: Test. ,replace

&gt;D/debug: test. ,replace

Why are the punctuation characters still present? How to get only the alphanumeric characters?

All Kotlin Android-Extensions Solutions on Gang of Coders

Total of 16 Kotlin Android-Extensions Solutions

Error:(1, 0) Plugin with id 'kotlin-android-extensions' not found