How to execute WPF assembly from memory?

Question

If the ms variable is a MemoryStream and contains a .Net assembly, you would normally run it like this:

var asm   = Assembly.Load(ms.ToArray());
var entry = asm.EntryPoint;
var inst  = asm.CreateInstance(entry.Name);
entry.Invoke(inst, null);

This works well on console applications and windows forms applications, however, WPF applications throw an exception:

Exception has been thrown by the target of an invocation.

With the inner exception of type System.IO.IOException:

Cannot locate resource 'mainwindow.xaml'.

The stacktrace is really big, but guessing from the start, it can't locate the resources when loaded from memory:

at MS.Internal.AppModel.ResourcePart.GetStreamCore(FileMode mode, FileAccess access)
at System.IO.Packaging.PackagePart.GetStream(FileMode mode, FileAccess access)
at System.IO.Packaging.PackagePart.GetStream()
at System.Windows.Application.LoadComponent(Uri resourceLocator, Boolean bSkipJournaledProperties)
at System.Windows.Application.DoStartup()
at System.Windows.Application.<.ctor>b__1(Object unused)
[...]

How could I fix this?

Answer 1

When you load an assembly dynamically from a MemoryStream, its working directory will be that of your own assembly. That directory is unlikely to contain the XAML markup files referred to by the assembly.

Try setting your Environment.CurrentDirectory to a new directory containing the necessary XAML, at least for the duration of the assembly loading and class instantiation.