Navigation Architecture Component - Action Navigation with lambda expression

Question

I have added a new action Navigation.xml:

 <fragment     android:id="@+id/launcher_home"     android:name="com.example.android.codelabs.navigation.MainFragment"     android:label="@string/home"     tools:layout="@layout/main_fragment">     <action         android:id="@+id/go_to_step_one"         app:destination="@id/flow_step_one" /> </fragment> 

When calling the navigation action, if i use, the navigation works correctly :

 view.findViewById<Button>(R.id.navigate_action_bt)?.setOnClickListener(             Navigation.createNavigateOnClickListener(R.id.go_to_step_one, null)     ) 

But when calling it with a lambda, it does not work :

 view.findViewById<Button>(R.id.navigate_action_bt)?.setOnClickListener {         Navigation.createNavigateOnClickListener(R.id.go_to_step_one, null)     } 

Answer 1

Well, that's the proper way of working. The method Navigation.createNavigateOnClickListener() returns a View.OnClickListener and according to the docs the proper way of assiging it is by using, even in Kotlin:

button.setOnClickListener(Navigation.createNavigateOnClickListener(R.id.next_fragment, null)); 

If you using the method inside the lambda, the lambda itself is the click listener so you're returning a click listener inside the click listener, that's why it isn't working. It's like doing this:

button.setOnClickListener {             View.OnClickListener {                 Toast.makeText(this, "hi", Toast.LENGTH_LONG).show()             }         } 

What you might be intrested in is this:

 view.findViewById<Button>(R.id.navigate_action_bt)?.setOnClickListener { view ->    view.findNavController().navigate(R.id.go_to_step_one) } 

Which will perform the navigation transition on button click.