Android databinding / MVVM pattern: computing view color based off Enum

Question

I have a class with the following enum and variables:

enum class ExerciseSetState {
    NOT_STARTED, PASSED, FAILED
}

@Entity
class ExerciseEntity(
        ... 
        @Ignore var setState: ExerciseSetState = ExerciseSetState.NOT_STARTED
        ....
 )

And in my databinding layout, I want to set the color based on this state variable:

<TextView
        android:id="@+id/tv_exer_rep_3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginTop="8dp"
        android:text="@{String.valueOf(exercise.setReps)}"
        android:backgroundColor="@{exercise.setState == ExerciseSetState.PASSED? (Color.GREEN : exercise.setState == ExerciseSetState.FAILED ? Color.RED: Color.TRANSPARENT )}"/>

Unfortunately I have this pretty horrible ternary expression in order to compute the color based off the value.

What is the idiomatic way of implementing this?

see Binding adapters

pskink
– pskink

2018-10-22 05:05:38 +00:00
Commented Oct 22, 2018 at 5:05 — pskink
– pskink, Commented Oct 22, 2018 at 5:05

Maksym V. · Accepted Answer · 2018-10-22 05:09:59Z

2

Make it simple with adapter:

 @BindingAdapter("xmlTag")
        public static void bindColor(TextView textView, @Nullable ExerciseSetState state) {
            //switch state and set the value
        }

in xml:

app:xmlTag="@{exercies.setState}"

answered Oct 22, 2018 at 5:09

Maksym V.

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3 Comments

Lanaru Over a year ago

Thank you. Where should I put the code for the binding adapter? It doesnt seem to fit in my WorkoutActivity or my WorkoutViewModel..

Maksym V. Over a year ago

just create a separate class for it

Lanaru Over a year ago

I did that. Thx.

Mohammad Fakhrpour · Accepted Answer · 2018-10-27 10:06:55Z

Create a Converter class and use it for converting enum to color

Layout:

<import type="*.Converter"/>
...

android:background="@{Converter.enumToColor(context, exercise.setState)}"

Converter Class:

class Converter {

    fun enumToColor(context: Context ,enum: ExerciseSetState) : Int {
        return when (enum){
            ExerciseSetState.NOT_STARTED -> getColor(context, R.color.colorAccent)
            ExerciseSetState.PASSED -> getColor(context, R.color.colorAccent)
            ExerciseSetState.FAILED -> getColor(context, R.color.colorAccent)
        }
    }
}

getColor helper method:

fun getColor(context: Context, colorId: Int): Int {
    return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        context.resources.getColor(colorId, null)
    } else {
        context.resources.getColor(colorId)
    }
}

and better to change setState to getState in here :)

Khemraj Sharma · Accepted Answer · 2018-10-22 10:29:09Z

0

You can simply specify colors in the enum. Because colors relate to enum.

enum class ExerciseSetState(var color: Int) {
    NOT_STARTED(Color.TRANSPARENT), PASSED(Color.GREEN), FAILED(Color.RED)
}

and

android:backgroundColor="@{exercise.setState.color}"

answered Oct 22, 2018 at 10:29

Khemraj Sharma

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1 Comment

Khemraj Sharma Over a year ago

And change setState to getState or state for better naming convention.

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