Vfrdtyky

addTextChangedListener() takes a TextWatcher which is an interface with 3 methods. What you wrote would only work if TextWatcher had only 1 method. I'm going to guess the error you're getting relates to your lambda not implementing the other 2 methods. You have 2 options going forward.

1) Ditch the lambda and just use an anonymous inner class

editText.addTextChangedListener(object : TextWatcher {

  override fun afterTextChanged(p0: Editable?) {

  }



  override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {

  }



  override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {

  }

})

2) Create an extension method so you can use a lambda expression:

fun EditText.afterTextChanged(afterTextChanged: (String) -> Unit) {

    this.addTextChangedListener(object : TextWatcher {

      override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {

      }



      override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {

      }



      override fun afterTextChanged(editable: Editable?) {

        afterTextChanged.invoke(editable.toString())

      }

    })

}

And then use the extension like so:

editText.afterTextChanged { doSomethingWithText(it) }

hope this Kotlin sample help making it clear:

class MainFragment : Fragment() {



    private lateinit var viewModel: MainViewModel



override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,

                          savedInstanceState: Bundle?): View {

    val view = inflater.inflate(R.layout.main_fragment, container, false)



    view.user.addTextChangedListener(object : TextWatcher {

        override fun beforeTextChanged(s: CharSequence, start: Int, count: Int, after: Int) {



        }



        override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {



        }



        override fun afterTextChanged(s: Editable) {

                userLayout.error =

                        if (s.length > userLayout.counterMaxLength) {

                            "Max character length is: ${userLayout.counterMaxLength}"

                        } else null

        }

    })

    return view

}



override fun onActivityCreated(savedInstanceState: Bundle?) {

    super.onActivityCreated(savedInstanceState)

    viewModel = ViewModelProviders.of(this).get(MainViewModel::class.java)

    // TODO: Use the ViewModel

   }

}

With this XML layout:

<android.support.design.widget.TextInputLayout

    android:id="@+id/userLayout"

    android:layout_width="match_parent"

    android:layout_height="wrap_content"

    app:counterMaxLength="5"

    app:counterEnabled="true"

    android:hint="user_name">



    <android.support.design.widget.TextInputEditText

        android:id="@+id/user"

        android:layout_width="match_parent"

        android:layout_height="wrap_content" />

</android.support.design.widget.TextInputLayout>

And this Gradle:

android {

    compileSdkVersion 'android-P'

...

}

    api 'com.android.support:design:28.0.0-alpha1'



    implementation 'com.android.support:appcompat-v7:28.0.0-alpha1' // appcompat library

A bit old, but using Kotlin Android extensions you can do something like that:

editTextRequest.textChangedListener {

            afterTextChanged {

                // Do something here...

            }

}

No extra code needed, just add:

implementation 'androidx.core:core-ktx:1.0.0'

Another alternative is the KAndroid library -

implementation 'com.pawegio.kandroid:kandroid:0.8.7@aar'

Then you could do something like this...

editText.textWatcher { afterTextChanged { doSomething() } }

Obviously it is excessive to use an entire library to solve your problem, but it also comes with a range of other useful extensions that eliminate boilerplate code in the Android SDK.

if you use implementation 'androidx.core:core-ktx:1.1.0-alpha05' you can use

For android.widget.TextView

TextWatcher 

TextView.doBeforeTextChanged(crossinline action: (text: CharSequence?, start: Int, count: Int, after: Int) -> Unit)

Add an action which will be invoked before the text changed.



TextWatcher 

TextView.doOnTextChanged(crossinline action: (text: CharSequence?, start: Int, count: Int, after: Int) -> Unit)

Add an action which will be invoked when the text is changing.



TextWatcher 

TextView.doAfterTextChanged(crossinline action: (text: Editable?) -> Unit)

https://developer.android.com/reference/kotlin/androidx/core/widget/package-summary#extension-functions

You can make use of kotlin's named parameters:

private val beforeTextChangedStub: (CharSequence, Int, Int, Int) -> Unit = { _, _, _, _ -> }

private val onTextChangedStub: (CharSequence, Int, Int, Int) -> Unit = { _, _, _, _ -> }

private val afterTextChangedStub: (Editable) -> Unit = {}



fun EditText.addChangedListener(

        beforeTextChanged: (CharSequence, Int, Int, Int) -> Unit = beforeTextChangedStub,

        onTextChanged: (CharSequence, Int, Int, Int) -> Unit = onTextChangedStub,

        afterTextChanged: (Editable) -> Unit = afterTextChangedStub

) = addTextChangedListener(object : TextWatcher {

    override fun beforeTextChanged(charSequence: CharSequence, i: Int, i1: Int, i2: Int) {

        beforeTextChanged(charSequence, i, i1, i2)

    }



    override fun onTextChanged(charSequence: CharSequence, i: Int, i1: Int, i2: Int) {

        onTextChanged(charSequence, i, i1, i2)

    }



    override fun afterTextChanged(editable: Editable) {

        afterTextChanged(editable)

    }

})