Is it possible to point one Color resource to another Color resource in Xamarin.Forms?

Question

I am building a Xamarin Forms Application and I am currently drawing up my application Resources, mainly my colours.

For example I have the following:

  <Color x:Key="Slate">#404040</Color>
  <Color x:Key="Blue">#458623</Color>

  <Color x:Key="SelectedItemColour">#458623</Color>

As you can see my SelectedItemColour is the same as the Blue.

I have tried the following but it didn't work:

  <Color x:Key="Slate">#404040</Color>
  <Color x:Key="Blue">#458623</Color>

  <Color x:Key="SelectedItemColour" Color="{StaticResource Blue}"/>

I know if WPF you can do the answer stated here

Is it possible to point a Colour Resource to another Colour Resource in Xamarin.Forms?

Answer 1

This may be an old question, but I was trying to accomplish this same thing for a project today and wanted a more elegant solution than the one proposed here. There doesn't seem to be a way to accomplish it purely with XAML, but this is the solution I ended up using.

First, I defined a utility class named ColorReference:

public class ColorReference : INotifyPropertyChanged
{
    private Color color = Color.Black;

    public Color Color
    {
        get => this.color;
        set
        {
            this.color = value;
            this.OnPropertyChanged();
        }
    }

    #region INotifyPropertyChanged

    public event PropertyChangedEventHandler PropertyChanged;

    [ NotifyPropertyChangedInvocator ]
    protected virtual void OnPropertyChanged([ CallerMemberName ] string propertyName = null)
    {
        this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    #endregion

    public static implicit operator Color(ColorReference colorReference) => colorReference.Color;
}

I'm not 100% positive that the INotifyPropertyChanged implementation is necessary but I figured it couldn't hurt (potentially allowing changing the color at runtime; I haven't tested this).

To use it, simply use it as a resource in a ResourceDictionary:

<Color x:Key="FirstColor">#51688f</Color>
...
<utility:ColorReference x:Key="SomeOtherColorName" Color="{StaticResource FirstColor}" />

In my use case, I'm using it to style Telerik controls with colors defined in my theme so that if I make a new theme, I don't need to copy the same color value all over the place. The obvious downside is that for any type other than Color, a new class would need to be defined, but I doubt I will need too many types to be aliased like this. Hopefully this helps someone else in the future trying to do the same thing I'm doing.