How to use an enum as a parameter of a function declaration within an interface?

Question

Is it possible to use an enum as a parameter of a function declaration within an interface? For example have:

class FloatingToastDialog(val messageType: FloatingToastType) {

    companion object {

        enum class FloatingToastType { Alert, Warning, Error }
    }        
    ...
}

I would like to declare in an interface a function that takes an enum as input parameter like so:

interface SecurityCallbacks {

    fun showFloatingToast(message: String, msgType: FloatingToastType)

}

but the compiler fails to import the enum by saying Unresolved reference: FloatingToastType

Is it possible to do that without using ordinals or other such escamotages?

Alexey Romanov · Accepted Answer · 2020-03-28 08:16:48Z

2

If you declare it this way, you have to refer to it as

fun showFloatingToast(message: String, msgType: FloatingToastDialog.Companion.FloatingToastType)

or

import FloatingToastDialog.Companion.FloatingToastType
...

fun showFloatingToast(message: String, msgType: FloatingToastType)

You can declare it inside the class directly and remove Companion:

class FloatingToastDialog(val messageType: FloatingToastType) {

    enum class FloatingToastType { Alert, Warning, Error }
    ...
}


fun showFloatingToast(message: String, msgType: FloatingToastDialog.FloatingToastType)

answered Mar 28, 2020 at 8:16

Alexey Romanov

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Comments

S.Bozzoni · Accepted Answer · 2020-03-28 09:20:02Z

2

You have to reference the enum inside a companion object this way: classame.Companion.enumtype

so, in your case, you can declare the interface like that :

interface SecurityCallbacks {
    fun showFloatingToast(message: String, msgType: FloatingToastDialog.Companion.FloatingToastType)
}

Alternativaly you can declare the enum inside the class FloatingToastDialog, not in the inner companion object and use it in the interface like that:

interface SecurityCallbacks {
        fun showFloatingToast(message: String, msgType: FloatingToastDialog.FloatingToastType)
    }

answered Mar 28, 2020 at 9:20

S.Bozzoni

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Comments

sciack · Accepted Answer · 2020-03-28 06:26:22Z

1

I think you have to declare the enum outside the class/companion object as package element, that should work. Also the enum should be in the interface.

answered Mar 28, 2020 at 6:26

sciack

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2 Comments

vitiello.antonio Over a year ago

Unfortunately it doesn't work that way either, and moving the enum to the interface would make no sense logically it's not SOLID

sciack Over a year ago

Usually you have concrete implementation that depends on interface not viceversa, but maybe you are in a scenario that make more sense the opposite approach.

Saksham Chaudhary · Accepted Answer · 2020-03-28 07:41:34Z

I'm from C# background but I think it'll be helpfull for you. I'm able to do it this way.If I skipped anything(or I need to tell java solution) feel free to point out.

using System;

public enum FloatingToastType {
    Alert, 
    Warning, 
    Error
}

interface SecurityCallbacks {
    void showFloatingToast(String message, FloatingToastType msgType);
}

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Main");
        FloatingToastDialog obj = new FloatingToastDialog();
        obj.showFloatingToast("Alert", FloatingToastType.Alert);
    }

}
class FloatingToastDialog : SecurityCallbacks
{
    public void showFloatingToast(String message, FloatingToastType messageType) 
    {
        Console.WriteLine(message + " " + messageType.ToString());
    }
}

It Gives the Output: Main Alert Alert

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