Android Studio unable to infer type of element define in xml

Issue

I have a layout xml where the following line occurs:

<androidx.constraintlayout.widget.ConstraintLayout
android:id="@+id/rootLayout"
...

and in Kotline I have the following line to refer to this element:

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

    setContentView(R.layout.activity_main)

    val rootLayout = findViewById(R.id.rootLayout)
    ...

The findViewById function is underlined in red telling 'Not enough information to infer type variable T'

Why is this happening. Clearly the type should be 'ConstraintLayout'

Why the error?

Solution

You must be using API level 26 (or above). This version has changed the signature of View.findViewById() - see here : https://developer.android.com/about/versions/oreo/android-8.0-changes#fvbi-signature

So in your case, where the result of findViewById is ambiguous, you need to supply the type:

1 Change :

val rootLayout = findViewById(R.id.rootLayout) 

val rootLayout = findViewById<ConstraintLayout>(R.id.rootLayout)

2 Change :

this.rootLayout = row?.findViewById(R.id.rootLayout)

this.rootLayout = row?.findViewById<ConstraintLayout>(R.id.rootLayout)

Note that in 2. the cast is only required because the row is nullable. If the label was nullable too, or if you made the row not nullable, it wouldn't be required.

Answered By - BADSHAH