Support for assets provided by library

[Daoting]

Current behavior

1. I create project with template "Cross-Platform Library".
2. Add the image file to the Assets directory of this project.
3. Set the build action to Content.
4. xaml
   <Image Source="ms-appx:///Bs.Kehu/Assets/header.png" />

The image is displayed in uwp and android. But in iOS:

2020-01-20 11:05:49.261049+0800 UnoApp[12385:168687] \^[[41m\^[[30mfail\^[[39m\^[[22m\^[[49m: Windows.UI.Xaml.Media.ImageSource[0]
      Unable to locate bundle resource [ms-appx:///Bs.Kehu/Assets/header.png]

Maybe it's not a bug. But I failed to get any help about this. I propose to add some help about this.
Thanks!

Expected behavior

How to reproduce it (as minimally and precisely as possible)

Environment

Nuget Package:

Package Version(s):

Affected platform(s):

• iOS
• Android
• WebAssembly
• WebAssembly renderers for Xamarin.Forms
• macOS
• Windows
• Build tasks
• Solution Templates

Visual Studio:

• 2017 (version: )
• 2019 (version: )
• for Mac (version: )

Relevant plugins:

• Resharper (version: )

Anything else we need to know?

[jeromelaban]

Thanks for the report! Indeed, this scenario is not yet supported.

[MartinZikmund]

@ajpinedam Are you planning to look into this?

[Juansero29]

This could be very useful for our use case, specially for fonts assets

[jeromelaban]

Until this issue is fixed, when working with a solution which contains a project with custom assets (assuming it is in a project named MyLibrary and the assets are located in a folder named Assets), a workaround can be to include the files as content from the consuming project (a project head, for instance), as such:

<ItemGroup>
    <Content Include="..\MyLibrary\Assets\**" Link="Assets\%(RecursiveDir)\%(FileName)%(Extension)" />
</ItemGroup>

This content could be located in a separate msbuild file (e.g. ProjectAssets.props), such as this one:

<Project>
   <ItemGroup>
      <Content Include="$(MSBuildThisFileDirectory)Assets\**" 
               Link="Assets\%(RecursiveDir)\%(FileName)%(Extension)" />
   </ItemGroup>
</Project>

And include it in the projects heads as follows:

<Import Project="..\MyLibrary\ProjectAssets.props" />

The path of the assets will local to the project head, though, with this workaround. WinUI prefixes assets with the library containing the assets (e.g. ms-apps://MyLibrary/Assets/MyAsset.txt), and this workaround will not include the library name.

The same workaround can be applied to nuget packages, and the contentfile convention.