Hi, how could we make this function work like a delegate property? ```fun TextView.drawableStart(dra...

# android

[Sergio C.]

Hi, how could we make this function work like a delegate property?

fun TextView.drawableStart(drawableRes: Int) {
    val drawable = ContextCompat.getDrawable(context, drawableRes)
    drawable?.setBounds(0, 0, drawable.intrinsicWidth, drawable.intrinsicHeight)
    setCompoundDrawables(drawable, null, null, null)
}

I want to do something like:

someTextview.drawableStart = R.drawable.someDrawable

[gildor]

do you mean:
var TextView.someDrawable: Int
set(drawableRes: Int) { … }

[gildor]

I just don’t see any delegation here, just standard extension property

[Sergio C.]

cool that's what I was looking for!

[Sergio C.]

var TextView.drawableStart: Int
    set(drawableRes: Int)  {
        val drawable = ContextCompat.getDrawable(context, drawableRes)
        drawable?.setBounds(0, 0, drawable.intrinsicWidth, drawable.intrinsicHeight)
        setCompoundDrawables(drawable, null, null, null)
    }
    get() {
        throw Error("Drawable Start Not available")
    }

It works but It must be a var and have a getter to work

[gildor]

Correct, it was a typo in my example, it cannot be val of course, if you need setter

[gildor]

You need getter with Int, you can do this:
var drawableStart: Int = -1
set(value) {
field = value
}

[gildor]

Not perfect, because it will have getter value only after first set, but imo better than exception

[Sergio C.]

Initializer is not allowed here because this property has no backing field

[gildor]

Still, function looks a bit more semantically correct for this case

[Sergio C.]

It doesn't work here

[Sergio C.]

It doesn't let me have an initializer

[Sergio C.]

probably because it's an extension on TextView

[gildor]

Should work

[Sergio C.]

no, try it

[gildor]

On phone

[gildor]

https://kotlinlang.org/docs/properties.html#backing-fields

[Sergio C.]

it's ok as is

[Sergio C.]

thanks for the help

[gildor]

Ahhhh

[gildor]

Sorry, you right, of course, it's extension

[gildor]

You can implement it by saving value to TV tags if want to make getter work

[gildor]

So no backing field, but getter will read from tags

[gildor]

Again, more like a workaround, it's not perfect because cannot get value before first initialization (same with backing field)

[Sergio C.]

using tags for the getter is an idea...
but for now I just need the setter, just to make reading the code easier.

[Sergio C.]

*getter

[gildor]

If you have a setter, you need a getter for property, this how properties work in Kotlin
Personally I would just use extension function for this case, because it's impossible to implement getter correctly, just to avoid possible confusion

[Sergio C.]

yes you are correct