Using lambda in custom BindingAdapter using Android Databinding and Kotlin - kotlin

Question

I'm trying to have a custom binding with a lambda handler for Android Databinding using Kotlin. It's working well as long as my ViewModel handler is explicitly returning Void. But if it returns Kotlin Unit instead, I get an error: cannot generate view binders java.lang.StackOverflowError.
Everything seems to be hooked-up correctly as all the other custom bindings works (convertBooleanToViewVisibility, toTestString and even customOnClick as long as I'm calling onClickVoid [see example below]).
The issue is when I'm trying to invoke a lambda returning Unit in my app:customOnClick instead of returning Void. In the example below, it's to invoke mainViewModel.onClick() instead of mainViewModel.onClickVoid(). There must be a way of making it work as the android:onClick is able to make to call to the Unit version. But if I'm using the same syntax for customOnClick calling onClick, I'm getting this error:
:app:kaptGenerateStubsDebugKotlin
Using kotlin incremental compilation
:app:kaptDebugKotlin
e: error: cannot generate view binders java.lang.StackOverflowError
e:
e: at android.databinding.tool.writer.Scope.access$getCurrentScope$cp(LayoutBinderWriter.kt:49)
e: at android.databinding.tool.writer.Scope$Companion.getCurrentScope(LayoutBinderWriter.kt:58)
e: at android.databinding.tool.writer.LayoutBinderWriterKt.scopedName(LayoutBinderWriter.kt:196)
e: at android.databinding.tool.expr.Expr.toCode(Expr.java:776)
e: at android.databinding.tool.writer.LayoutBinderWriterKt$callbackLocalName$2.invoke(LayoutBinderWriter.kt:203)
e: at android.databinding.tool.writer.LayoutBinderWriterKt$callbackLocalName$2.invoke(LayoutBinderWriter.kt)
e: at android.databinding.tool.ext.LazyExt.getValue(ext.kt:27)
e: at android.databinding.tool.writer.LayoutBinderWriterKt.getCallbackLocalName(LayoutBinderWriter.kt)
e: at android.databinding.tool.writer.LayoutBinderWriterKt.scopedName(LayoutBinderWriter.kt:197)
e: java.lang.IllegalStateException: failed to analyze: java.lang.RuntimeException: failure, see logs for details.
cannot generate view binders java.lang.StackOverflowError
at android.databinding.tool.writer.Scope.access$getCurrentScope$cp(LayoutBinderWriter.kt:49)
at android.databinding.tool.writer.Scope$Companion.getCurrentScope(LayoutBinderWriter.kt:58)
at android.databinding.tool.writer.LayoutBinderWriterKt.scopedName(LayoutBinderWriter.kt:196)
at android.databinding.tool.expr.Expr.toCode(Expr.java:776)
at android.databinding.tool.writer.LayoutBinderWriterKt$callbackLocalName$2.invoke(LayoutBinderWriter.kt:203)
at android.databinding.tool.writer.LayoutBinderWriterKt$callbackLocalName$2.invoke(LayoutBinderWriter.kt)
at android.databinding.tool.ext.LazyExt.getValue(ext.kt:27)
at android.databinding.tool.writer.LayoutBinderWriterKt.getCallbackLocalName(LayoutBinderWriter.kt)
at android.databinding.tool.writer.LayoutBinderWriterKt.scopedName(LayoutBinderWriter.kt:197)
.............................. (TRUNCATED) ...................................
at android.databinding.tool.expr.Expr.toCode(Expr.java:776)
at android.databinding.tool.writer.LayoutBinderWriterKt$callbackLocalName$2.invoke(LayoutBinderWriter.kt:203)
at android.databinding.tool.writer.LayoutBinderWriterKt$callbackLocalName$2.invoke(LayoutBinderWriter.kt)
at android.databinding.tool.ext.LazyExt.getValue(ext.kt:27)
at android.databinding.tool.writer.LayoutBinderWriterKt.getCallbackLocalName(LayoutBinderWriter.kt)
at android.databinding.tool.writer.LayoutBinderWriterKt.scopedName(LayoutBinderWriter.kt:197)
at org.jetbrains.kotlin.analyzer.AnalysisResult.throwIfError(AnalysisResult.kt:57)
at org.jetbrains.kotlin.cli.jvm.compiler.KotlinToJVMBytecodeCompiler.compileModules(KotlinToJVMBytecodeCompiler.kt:144)
at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecute(K2JVMCompiler.kt:167)
at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecute(K2JVMCompiler.kt:55)
at org.jetbrains.kotlin.cli.common.CLICompiler.exec(CLICompiler.java:182)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.execCompiler(CompileServiceImpl.kt:397)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.access$execCompiler(CompileServiceImpl.kt:99)
at org.jetbrains.kotlin.daemon.CompileServiceImpl$compile$1$2.invoke(CompileServiceImpl.kt:365)
at org.jetbrains.kotlin.daemon.CompileServiceImpl$compile$1$2.invoke(CompileServiceImpl.kt:99)
at org.jetbrains.kotlin.daemon.CompileServiceImpl$doCompile$2$$special$$inlined$withValidClientOrSessionProxy$lambda$1.invoke(CompileServiceImpl.kt:798)
at org.jetbrains.kotlin.daemon.CompileServiceImpl$doCompile$2$$special$$inlined$withValidClientOrSessionProxy$lambda$1.invoke(CompileServiceImpl.kt:99)
at org.jetbrains.kotlin.daemon.common.DummyProfiler.withMeasure(PerfUtils.kt:137)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.checkedCompile(CompileServiceImpl.kt:825)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.access$checkedCompile(CompileServiceImpl.kt:99)
at org.jetbrains.kotlin.daemon.CompileServiceImpl$doCompile$2.invoke(CompileServiceImpl.kt:797)
at org.jetbrains.kotlin.daemon.CompileServiceImpl$doCompile$2.invoke(CompileServiceImpl.kt:99)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.ifAlive(CompileServiceImpl.kt:1004)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.ifAlive$default(CompileServiceImpl.kt:865)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.doCompile(CompileServiceImpl.kt:791)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.access$doCompile(CompileServiceImpl.kt:99)
at org.jetbrains.kotlin.daemon.CompileServiceImpl$compile$1.invoke(CompileServiceImpl.kt:364)
at org.jetbrains.kotlin.daemon.CompileServiceImpl$compile$1.invoke(CompileServiceImpl.kt:99)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.ifAlive(CompileServiceImpl.kt:1004)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.ifAlive$default(CompileServiceImpl.kt:865)
at org.jetbrains.kotlin.daemon.CompileServiceImpl.compile(CompileServiceImpl.kt:336)
at sun.reflect.GeneratedMethodAccessor86.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:324)
at sun.rmi.transport.Transport$1.run(Transport.java:200)
at sun.rmi.transport.Transport$1.run(Transport.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
... 39 more
FAILED
Any idea how to make it work with Unit so I do not need to change my ViewModel to explicitly return Void? for all my handlers?
Sample project
Project build.gradle
buildscript {
ext.kotlin_version = '1.1.3-2'
ext.plugin_version = '2.3.3'
repositories {
jcenter()
}
dependencies {
classpath "com.android.tools.build:gradle:$plugin_version"
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
}
}
allprojects {
repositories {
jcenter()
mavenCentral()
}
}
task clean(type: Delete) {
delete rootProject.buildDir
}
Module (app) build.gradle
buildscript {
repositories {
jcenter()
mavenCentral()
}
dependencies {
classpath "org.jetbrains.kotlin:kotlin-android-extensions:$kotlin_version"
}
}
apply plugin: 'com.android.application'
apply plugin: "kotlin-android"
apply plugin: 'kotlin-android-extensions'
apply plugin: 'kotlin-kapt'
android {
compileSdkVersion 24
buildToolsVersion "25.0.2"
defaultConfig {
applicationId "com.example.kotlindatabinding"
minSdkVersion 24
targetSdkVersion 24
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
dataBinding {
enabled = true
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
sourceSets {
main.java.srcDirs += 'src/main/kotlin'
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
exclude group: 'com.android.support', module: 'support-annotations'
})
compile 'com.android.support:appcompat-v7:26.+'
compile 'com.android.support.constraint:constraint-layout:1.0.2'
testCompile 'junit:junit:4.12'
compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
kapt "com.android.databinding:compiler:$plugin_version"
}
kapt {
generateStubs = true
}
MainActivity.kt
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val binding = DataBindingUtil.setContentView<ActivityMainBinding>(this, R.layout.activity_main)
binding.setMainViewModel(MainViewModel())
}
}
MainViewModel.kt
class MainViewModel {
val myName: String
get() {
return "Hello world!"
}
fun onClick(){
Log.i("ME", "Logging...")
}
fun onClickVoid(): Void? {
onClick()
return null as Void?
}
}
Bindings.kt
object Bindings{
#BindingConversion
#JvmStatic fun convertBooleanToViewVisibility(isVisible: Boolean): Int {
// Working
return if (isVisible) View.VISIBLE else View.GONE
}
#BindingAdapter("customOnClick")
#JvmStatic fun setOnItemClicked(textView: TextView, consumer: (String) -> Any?) {
// Working
consumer("test")
}
#JvmStatic fun toTestString(input: Any) : String {
return "Test"
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<layout 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">
<data>
<import type="com.example.kotlindatabinding.Bindings"/>
<variable
name="mainViewModel"
type="com.example.kotlindatabinding.MainViewModel" />
</data>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.kotlindatabinding.MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#{Bindings.toTestString(mainViewModel.myName)}"
android:visibility="#{mainViewModel.myName != null}"
android:clickable="true"
android:onClick="#{() -> mainViewModel.onClick()}"
app:customOnClick="#{(someInput) -> mainViewModel.onClickVoid()}" />
</LinearLayout>
</layout>

Answer 1

Well, very late response I suppose, but others might had the same issue:
As far as I see this is on a false assumption: databinding uses Java and doesn't know about Kotlin in general.
In order to set a listener via databinding you have to use a Java interface with a method. Kotlin lambdas are not like Java interfaces with a simple method since they contain functions, meaning they always return something (if not specified then Unit).
So to achieve setting a listener define a simple Java interface as a parameter in the binding adapter

Answer 2

Move this code outside the default config block. Put it inside
android {
dataBinding {
enabled = true
}
}