WPF Image source from constant

Question

I've got some icons that are resources in my project and I plan to use these icons for menu items and other things.

I've created a constants class to hold the locations of these icons in a central location rather than hardcoding them into each menu item etc.

E.g.

public const string IconName = "/Project;component/Icons/IconName.png";

If I hardcode this value into the Source property of an image in xaml it works fine. However, if I try to reference this constant then it fails.

E.g.

<Image Source="{x:Static pb:IconConstants.IconName}" Width="16" Height="16" />

It fails with this exception: "Cannot convert the value in attribute 'Source' to object of type 'System.Windows.Media.ImageSource'. ".

What is the difference between this and me just hardcoding the value? Is there a better way of referencing my constants in xaml?

Thanks, Alan

Answer 1

The difference is that in first case (when you hardcode the path) the XAML parser will invoke a value converter (ImageSourceConverter) for the string you specify in the Source attribute to convert it to a value of type ImageSource. While in second case it expects that value of your constant will already be of type ImageSource.

What you can do is you can put all the paths in a global ResourceDictionary:

<Window.Resources>
    <ResourceDictionary>
        <BitmapImage x:Key="IconName">/Project;component/Icons/IconName.png</BitmapImage>
    </ResourceDictionary>
</Window.Resources>

<Image Source="{StaticResource IconName}" Width="16" Height="16" />

---

If you want to store the path constants in the code, you can have Uri objects as contants and set the UriSource property of BitmapImage to this URI:

public static readonly Uri IconName = new Uri("/Project;component/Icons/IconName.png", UriKind.Relative); 

<BitmapImage x:Key="IconName" UriSource="{x:Static pb:IconConstants.IconName}"/>