How would you extend TextView using some method?

You can create a custom class by inheriting from TextView and overriding the necessary methods or adding your own.

For example, to add a custom text display:

class CustomTextView(context: Context, attrs: AttributeSet? = null) : AppCompatTextView(context, attrs) {

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        // Additional drawing or appearance modifications
    }

    fun setCustomText(newText: String) {
        text = newText.toUpperCase() // Simple extension of functionality
    }
}

Or to handle special attributes via XML:

<com.example.yourapp.CustomTextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!"
    app:customAttribute="someValue" />

where app:customAttribute is processed inside CustomTextView through obtainStyledAttributes.

Another approach is to use Extension Functions in Kotlin to add methods to the existing TextView class without creating a subclass, for example:

fun TextView.setTextWithAnimation(newText: String, duration: Long = 300) {
    // Implementation of animation when changing text
}