More details on Listing9.7

class CrimeDetailFragment: Fragment() {
    private lateinit var binding: FragmentCrimeDetailBinding
    private lateinit var crime: Crime

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        crime = Crime(
            id = UUID.randomUUID(),
            title = " ",
            date = Date(),
            isSolved = false
        )
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        binding = FragmentCrimeDetailBinding.inflate(layoutInflater,container,false)
        return super.onCreateView(inflater, container, savedInstanceState)
    }
}

I am curious on this question:

Why does Fragment not have this layoutInflater property, but knows to call getLayoutInflater() to get it from Activity? Is this a Kotlin syntax feature?

I got answer from OpenAI:
Great question! The reason Fragment does not have a layoutInflater property but still allows you to access it as if it does, is a combination of Kotlin’s property syntax sugar and how Android’s framework methods work in Java.


:one: Why doesn’t Fragment have a layoutInflater property?

If you check the Android source code, you’ll see that Fragment does not define layoutInflater as a property. Instead, it only provides the getLayoutInflater() method:

public LayoutInflater getLayoutInflater() {
    return requireActivity().getLayoutInflater();
}

This means there is no actual field called layoutInflater in Fragment.


:two: Why can we access layoutInflater like a property in Kotlin?

This is due to Kotlin’s method-to-property conversion feature:

  • In Java, methods like getLayoutInflater() must be explicitly called:
    LayoutInflater inflater = fragment.getLayoutInflater();
    
  • But in Kotlin, thanks to automatic property mapping, you can write it as fragment.layoutInflater, and Kotlin automatically calls getLayoutInflater() behind the scenes:
    val inflater = fragment.layoutInflater  // âś… Kotlin calls getLayoutInflater()
    

:point_right: Kotlin turns any Java method named getXxx() into a property-like access xxx!
This is why layoutInflater appears as if it’s a property, even though it’s actually a method call.


:three: Where does layoutInflater come from in Fragment?

Since Fragment itself doesn’t store a LayoutInflater, it calls requireActivity().getLayoutInflater(), which means it delegates the request to its parent Activity.

This means:

  • If the Fragment is attached to an Activity, it fetches the LayoutInflater from that Activity.
  • If the Fragment is not attached yet, calling layoutInflater will throw an exception because requireActivity() would fail.

:four: Is this a Kotlin-specific syntax feature?

Yes and no. Here’s why:

:white_check_mark: Kotlin Feature:

  • Kotlin automatically converts getXxx() into a property-like syntax (xxx).
  • This makes fragment.layoutInflater look like a property, even though it’s actually calling getLayoutInflater().

:x: Not Kotlin-Specific:

  • The fact that getLayoutInflater() fetches it from Activity is an Android framework design choice, not a Kotlin feature.
  • Even in Java, Fragment would have to call getLayoutInflater() to get it from Activity.

:five: What happens under the hood?

When you write:

val inflater = fragment.layoutInflater

It is actually compiled into:

LayoutInflater inflater = fragment.getLayoutInflater();

This transformation is completely automatic and makes Kotlin more concise and readable.


:fire: Summary

  1. Fragment does not have a layoutInflater property.
  2. Kotlin automatically maps getLayoutInflater() to layoutInflater due to its method-to-property syntax sugar.
  3. Fragment fetches LayoutInflater from Activity using getLayoutInflater(), meaning it doesn’t store its own instance.
  4. This is both a Kotlin language feature (syntactic sugar) and an Android framework design choice.

Kotlin’s property syntax makes fragment.layoutInflater look and feel like a real property, even though it’s actually a method call. :rocket:

1 Like