Windows Workflow Syntax Editor Integration Sample Question

Hello, thank you for evaluating SyntaxEditor.

Is the custom assembly changing continuously (what is the error)?  If not, one thing you can possibly do is just create a single static project assembly and use that in each editor instance.  That way it only loads once and is probably better anyhow since the editor instance will be getting created repeatedly.

We have a TODO list item to possibly look into using Cecil or CCI as an alternative to reflection.  We can't include those in the main product though because they are third-party, so they would need to be optional add-ons that just wrap the assembly loading and create the appropriate IBinaryAssembly.  That being said, the current method does work all right in most cases.

Question: Is the custom assembly changing?  
Answer:  In most cases the custom assembly will not be changing.  
(In theory, someone migh accidently select the wrong assembly when addng a reference and need to unload it, then browse to the correct assembly.  That could present a problem.  But in our case, the custom assemblies should not be changing.) 

Question:  What is the error?
Answer:  When the following code executes the first time, I have 5 items in the Assembly References collection.  When the code executes the second time, I only have 4 items in the collection.  No error is thrown.  The custom.dll is just not added.  I was hoping the the AddFrom method would detect that the assembly was already loaded in the process space and get the reflection data from the in process assembly, or better from the ambient assembly repository provider.

// Add some common assemblies for reflection (any custom assemblies could be added using various Add overloads instead)
projectAssembly.AssemblyReferences.AddMsCorLib();
projectAssembly.AssemblyReferences.Add("System");
projectAssembly.AssemblyReferences.Add("System.Core");
projectAssembly.AssemblyReferences.Add("System.Xml");
projectAssembly.AssemblyReferences.AddFrom(@"C:\Test\Custom.dll");

Question:  Could I use a Static Project Assembly?
Answer:  I agree that recreating the Project Assembly is not the best idea. I will expore a static Project Assembly.  

Note: I was able to work around the problem by creating my own method that handles Adding AssemblyReferences.  It first checks the ambient assembly repository cache path for a Dat file.  If it exist, I load the Dat, otherwise it loads the Dll.  As long as the Dll does not change and I don't prune the cache this seems to work.  This is similar to precreating the Dat files and loading the from a resource, but it happens at run time.

I was debating about trying to find a way to perform the AssemblyReferences.AddFrom in a different App Domain.  The advantage of this is I could populate the Cache and unload the App Domain to unload the assemblies.  This would give me a ReflectionOnly Load without actually loading the assembly.  But AppDomains are kind of a pain to work with.

Overall I am very impressed with the suite of controls.  Thank you.

I believe the ambient assembly repository provider stores the number of references for each assembly from the ProjectAssembly objects.  So if you drop all references to it, it will remove the assembly info from the assembly repository provider to free up memory.  Still it should be able to load the Custom.dll file again ok.  Unless there is some pruning or something going on at the time it's trying to load (perhaps a file lock issue)?  If you set VS to break on all thrown CLR exceptions, maybe you can catch what's going on there.

The exception is a FileLoadException.

API restriction: The assembly '' has already loaded from a different location. It cannot be loaded from a new location within the same appdomain.

My guess is the following method:

projectAssembly.AssemblyReferences.AddFrom()

 is reading the assembly into a byte array and then using a ReflectionOnlyLoad().

It is the same exception you get if you run this code.

using System.Reflection;
class Program
{
    static void Main(string[] args)
    {
        byte[] fileAsBytes = System.IO.File.ReadAllBytes(@"C:\Test\Custom.dll");
        Assembly.ReflectionOnlyLoad(fileAsBytes);
        Assembly.ReflectionOnlyLoad(fileAsBytes);  // exception here
    }
}

Just for contrast the following code, which uses ReflectionOnlyLoadFrom, DOES NOT throw an exception.

using System.Reflection;
class Program
{
    static void Main(string[] args)
    {   
        Assembly.ReflectionOnlyLoadFrom(@"C:\Test\Custom.dll");
        Assembly.ReflectionOnlyLoadFrom(@"C:\Test\Custom.dll");
    }
}

To duplicate this behavior in the Actipro and Windows Workflow Integration sample do the following.

1) Create a .Net dll with a namespace called "Test". Create a public class with a public method.  Call it Custom.dll.

2) Modify the sample code by adding one line to the DotNetProjectAssemblyReferenceLoader method.

projectAssembly.AssemblyReferences.AddFrom(@"C:\Test\Custom.dll");

 3) Run the program.

4) Give focus to the To part of the Assign activity and type:  new T    You should see the intellisense with your custom namespace.

5) Give focus to the Text part of the WriteLine Activity and type:  new T  You will not see your namespace because the assembly would not load for the new instance.

I have several options to workaround this issue. Overall the tool, documenation, and this forum has been outstanding.  Thank you.

Thanks for the reply.

I believe we used to use ReflectionOnlyLoadFrom but then found that it locks the file.  So if someone tried to compile a new assembly at that path, it couldn't be written.  The ReadAllBytes version at least didn't lock the file.

One thing you might try is doing a shadow copy.  Perhaps copy the .dll to another new unique filename, load from that using our method, and then delete the file later on when done.

The best solution is to use one of those non-reflection ways to read the assembly info, and hopefully we can get one of those written in the future.

Would it be possible to receive the sample project integration with Windows Workflow? I am currently researching a solution to add intellisense to my rehosted workflow designer.

Hi Gerald,

Yes certainly.  Please email our support address and we'll send you the link.

Will do!