Retrieve Arguments of a Workflow (with default values)? - workflow-foundation-4

Question

Given is a Workflow Foundation 4 runtime that is working against a website ;)
We need to get the arguments of workflows to show the user an editor to enter the arguments. For that we need all arguments with names, types and - default values, as well as an indication whether an argument is required.
Workflows are stored as XAML files.
How to do that? The data seems to be in the Activity Metadata which seems to be not avaialble outside the Workflow. In addition, the Workflow Engine ModelService is for the Designer and has a lot of overhead.
Any easy way to retrieve this information?

Answer 1

I've already done something similar. Reflection might be your best (and only) option if you want a generic approach.
// Just an holder for InArgument informations
class InArgumentInfo
{
public string InArgumentName { get; set; }
public string InArgumentDescription { get; set; }
public bool InArgumentIsRequired { get; set; }
}
static ICollection<InArgumentInfo> GetInArgumentsInfos(Activity activity)
{
var properties = activity.GetType()
.GetProperties()
.Where(p => typeof(InArgument).IsAssignableFrom(p.PropertyType))
.ToList();
var argumentsCollection = new Collection<InArgumentInfo>();
foreach (var property in properties)
{
var descAttribute = property
.GetCustomAttributes(false)
.OfType<DescriptionAttribute>()
.FirstOrDefault();
string description = descAttribute != null && !string.IsNullOrEmpty(descAttribute.Description) ?
descAttribute.Description :
string.Empty;
bool isRequired = property
.GetCustomAttributes(false)
.OfType<RequiredArgumentAttribute>()
.Any();
argumentsCollection.Add(new InArgumentInfo
{
InArgumentName = property.Name,
InArgumentDescription = description,
InArgumentIsRequired = isRequired
});
}
return argumentsCollection;
}
This way you can not only retrieve the argument's name but also other information hold by the argument's attributes. For example I choose to give argument an user-friendly name through [Description] attribute (eg. instead of MyPropertyName user sees "My Property Name").
Note: if you can ensure that you activity is an ActivityBuilder or DynamicActivity they both have Properties property that you can use, but the principle is the same.

Answer 2

Load it as DynamicActivity and iterate over Properties property
var dynamicActivity = ActivityXamlServices.Load(foo) as DynamicActivity
foreach(DynamicActivityProperty prop in dynamicActivity.Properties)
{
// ...
}
UPDATE: Missed default value part
foreach (var prop in dynamicActivity .Properties)
{
object defaultValue;
if (prop.Value == null)
{
defaultValue = null;
}
else
{
Type genericTypeDefinition = prop.Type.GetGenericTypeDefinition();
if (genericTypeDefinition == typeof(InArgument<>) || genericTypeDefinition == typeof(InOutArgument<>))
{
var valueProp = prop.Value.GetType().GetProperty("Expression", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.DeclaredOnly);
var expression = valueProp.GetValue(prop.Value, null);
var expressionValueProp = expression.GetType().GetProperty("Value");
defaultValue = expressionValueProp.GetValue(expression, null);
}
}
}
Not totally guaranteed, there are some checks you have to do.