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    <p>I didn't like the idea of using ModuleDependency because this would mean that module a would not load when module b was not present, when in fact there was no dependency. Instead I created a priority attribute to decorate the module:</p> <pre><code>/// &lt;summary&gt; /// Allows the order of module loading to be controlled. Where dependencies /// allow, module loading order will be controlled by relative values of priority /// &lt;/summary&gt; [AttributeUsage(AttributeTargets.Class, AllowMultiple = false)] public sealed class PriorityAttribute : Attribute { /// &lt;summary&gt; /// Constructor /// &lt;/summary&gt; /// &lt;param name="priority"&gt;the priority to assign&lt;/param&gt; public PriorityAttribute(int priority) { this.Priority = priority; } /// &lt;summary&gt; /// Gets or sets the priority of the module. /// &lt;/summary&gt; /// &lt;value&gt;The priority of the module.&lt;/value&gt; public int Priority { get; private set; } } </code></pre> <p>I then decorated the modules like this:</p> <pre><code>[Priority(200)] [Module(ModuleName = "MyModule")] public class MyModule : IModule </code></pre> <p>I created a new descendent of DirectoryModuleCatalog:</p> <pre><code>/// &lt;summary&gt; /// ModuleCatalog that respects PriorityAttribute for sorting modules /// &lt;/summary&gt; [SecurityPermission(SecurityAction.InheritanceDemand), SecurityPermission(SecurityAction.LinkDemand)] public class PrioritizedDirectoryModuleCatalog : DirectoryModuleCatalog { /// &lt;summary&gt; /// local class to load assemblies into different appdomain which is then discarded /// &lt;/summary&gt; private class ModulePriorityLoader : MarshalByRefObject { /// &lt;summary&gt; /// Get the priorities /// &lt;/summary&gt; /// &lt;param name="modules"&gt;&lt;/param&gt; /// &lt;returns&gt;&lt;/returns&gt; [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic"), System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Reliability", "CA2001:AvoidCallingProblematicMethods", MessageId = "System.Reflection.Assembly.LoadFrom")] public Dictionary&lt;string, int&gt; GetPriorities(IEnumerable&lt;ModuleInfo&gt; modules) { //retrieve the priorities of each module, so that we can use them to override the //sorting - but only so far as we don't mess up the dependencies var priorities = new Dictionary&lt;string, int&gt;(); var assemblies = new Dictionary&lt;string, Assembly&gt;(); foreach (ModuleInfo module in modules) { if (!assemblies.ContainsKey(module.Ref)) { //LoadFrom should generally be avoided appently due to unexpected side effects, //but since we are doing all this in a separate AppDomain which is discarded //this needn't worry us assemblies.Add(module.Ref, Assembly.LoadFrom(module.Ref)); } Type type = assemblies[module.Ref].GetExportedTypes() .Where(t =&gt; t.AssemblyQualifiedName.Equals(module.ModuleType, StringComparison.Ordinal)) .First(); var priorityAttribute = CustomAttributeData.GetCustomAttributes(type).FirstOrDefault( cad =&gt; cad.Constructor.DeclaringType.FullName == typeof(PriorityAttribute).FullName); int priority; if (priorityAttribute != null) { priority = (int)priorityAttribute.ConstructorArguments[0].Value; } else { priority = 0; } priorities.Add(module.ModuleName, priority); } return priorities; } } /// &lt;summary&gt; /// Get the priorities that have been assigned to each module. If a module does not have a priority /// assigned (via the Priority attribute) then it is assigned a priority of 0 /// &lt;/summary&gt; /// &lt;param name="modules"&gt;modules to retrieve priorities for&lt;/param&gt; /// &lt;returns&gt;&lt;/returns&gt; private Dictionary&lt;string, int&gt; GetModulePriorities(IEnumerable&lt;ModuleInfo&gt; modules) { AppDomain childDomain = BuildChildDomain(AppDomain.CurrentDomain); try { Type loaderType = typeof(ModulePriorityLoader); var loader = (ModulePriorityLoader) childDomain.CreateInstanceFrom(loaderType.Assembly.Location, loaderType.FullName).Unwrap(); return loader.GetPriorities(modules); } finally { AppDomain.Unload(childDomain); } } /// &lt;summary&gt; /// Sort modules according to dependencies and Priority /// &lt;/summary&gt; /// &lt;param name="modules"&gt;modules to sort&lt;/param&gt; /// &lt;returns&gt;sorted modules&lt;/returns&gt; protected override IEnumerable&lt;ModuleInfo&gt; Sort(IEnumerable&lt;ModuleInfo&gt; modules) { Dictionary&lt;string, int&gt; priorities = GetModulePriorities(modules); //call the base sort since it resolves dependencies, then re-sort var result = new List&lt;ModuleInfo&gt;(base.Sort(modules)); result.Sort((x, y) =&gt; { string xModuleName = x.ModuleName; string yModuleName = y.ModuleName; //if one depends on other then non-dependent must come first //otherwise base on priority if (x.DependsOn.Contains(yModuleName)) return 1; //x after y else if (y.DependsOn.Contains(xModuleName)) return -1; //y after x else return priorities[xModuleName].CompareTo(priorities[yModuleName]); }); return result; } } </code></pre> <p>Finally, I changed the bootstrapper to use this new catalog:</p> <pre><code> /// &lt;summary&gt;Where are the modules located&lt;/summary&gt; /// &lt;returns&gt;&lt;/returns&gt; protected override IModuleCatalog GetModuleCatalog() { return new PrioritizedDirectoryModuleCatalog() { ModulePath = @".\Modules" }; } </code></pre> <p>I'm not sure if the stuff with assembly loading is the best way to do things, but it seems to work...</p>
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    1. CO+1 I have wanted to know how to do this for quite some time. Thank you very, very much.
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    2. COExcellent solution, exactly what I was looking for!
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