Kotlin：未解决的参考：alpha

Question

I don't understand why, on a project that use Java and Kotlin, in Kotlin I have issues calling some methods of the View class.

If I try to modify the alpha of my AppCompatButton

binding.button.alpha = 0.5F

of if I directly try to modify the alpha on a newly created View

val view = View(context)
view.alpha = 1F

I have the following error

Execution failed for task ':app:compileAllDebugKotlin'. Unresolved reference: alpha

Some methods of the View class works some don't.

Answer 1

That's very strange, because View class has the alpha property and it should work.

• https://developer.android.com/reference/android/view/View#getAlpha()
• https://developer.android.com/reference/android/view/View#setAlpha(float)

Make sure that you have API level >= 11 and that you have a correct imports:

import android.view.View