I am quite new to WPF, and quite recently in my spare time while working on a hobby project I came across a very similar problem, with similar constraints.
Nonetheless, as you already figured, application works fine at design time but not at runtime while siteoforigin is the vice versa. As such one logical way to solve this problem is to simply use both, siteoforigin at runtime and application at design time.
To do this, you will simply need to intercept the setting of Source property of your control. One way to do this is to use inheritance.
The following is an example which does this for a ResourceDictionary:
Implementation
/// <summary>
/// A modified type of <see cref="ResourceDictionary"/> that translates "Resource" pack URIs to "Site of Origin"
/// pack URIs when in runtime.
///
/// i.e. This allows you to declare pack URIs as "pack://application:,,,", which will be resolved
/// as such in design mode while at runtime, actually using "pack://siteoforigin:,,,".
/// </summary>
public class SiteOfOriginResourceDictionary : ResourceDictionary
{
private const string SiteOfOriginPrefix = "pack://siteoforigin:,,,";
private const string ApplicationPrefix = "pack://application:,,,";
private const string UseRedirectSource = "Please use RedirectSource instead of Source";
private string _originalUri;
/// <summary>
/// Gets or sets the design time source.
/// </summary>
public string RedirectSource
{
get => _originalUri;
set
{
this._originalUri = value;
bool isInDesignMode = (bool) DesignerProperties.IsInDesignModeProperty.GetMetadata(typeof(DependencyObject)).DefaultValue;
if (! isInDesignMode)
{
if (value.Contains(ApplicationPrefix))
value = value.Replace(ApplicationPrefix, SiteOfOriginPrefix);
}
base.Source = new Uri(value);
}
}
/// <summary>
/// Please use <see cref="RedirectSource"/> instead.
/// </summary>
public new Uri Source
{
get => throw new Exception(UseRedirectSource);
set => throw new Exception(UseRedirectSource);
}
}
Usage Example
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<SiteOfOriginResourceDictionary RedirectSource="pack://application:,,,/Theme/Default/Root.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</ResourceDictionary.MergedDictionaries>
In practice, this solution has worked for me and I make active use of this code. I'm quite certain you can do the same with an Image and/or other WPF components.
That said, in my case, I only needed to support this on a ResourceDictionary. This solution would be unoptimal in your case as you would probably (eventually) require to do this for multiple controls down the road.
As such, I would propose as a potential solution to further investigate the use of Attached Properties, making a an attached property that sets the Source of a control, switching between application at design time and siteoforigin at runtime.
That instead could be re-used across multiple controls without having to inherit each time for each new control/class.
On a related note, I can't say I know why using application works in the designer when the build action for a resource is set to Content. According to the documentation this URI is to be used when a resource "is compiled into a referenced assembly" (Source), but nonetheless this works for me.
This is my first post on StackOverflow and I'm a hobbyist, so please take it easy on me .
