A day in the life...

ASP MVC Silverlight control not appearing–404 not found

Peter Morris — Thu, 10 Nov 2011 11:17:50 GMT

Just a quick tip in case you have deployed your ASP MVC app with silverlight controls in it which are not appearing. I experienced this recently when deploying to IIS6. The solution is

Open the IIS manager app (Start->Admin->Internet Information Services (IIS) Manager)
Expand the local computer node
Then expand the Websites nodes
Right-click your website and select “Properties”
Click the “Http Headers” tab
At the bottom of the page click the “MIME Types” button
Click the “New” button
For the extension type in .xap
For the MIME Type type in application/x-silverlight-app

All done

Identified associations (maps)

Peter Morris — Tue, 12 Apr 2011 09:57:41 GMT

I thought I’d share this approach to having named associations. Let’s say you have an Address class with a Name property on it, your Employee can have a property like this

1 var homeAddress = new Address(.....);
2 homeAddress.Line1 = "192 Blah Street";
3 homeAddress.Line2 = "etc";
4 employee.Addresses["Home"] = homeAddress;
5 
6 var workAddress = new Address(.....);
7 workAddress.Line1 = "123 Meh Road";
8 workAddress.Line2 = "etc";
9 employee.Addresses["Work"] = workAddress;

Once you have created your Employee and Address classes add a private association from Employee to Address named something like _Addresses. Then add the following code to the Employee class.

 1 IdentifiedAssociation<string, NamedPostalAddress> postalAddresses;
 2 public IdentifiedAssociation<string, NamedPostalAddress> PostalAddresses
 3 {
 4   get
 5   {
 6     if (postalAddresses == null)
 7       postalAddresses = new IdentifiedAssociation<string, NamedPostalAddress>(
 8         //Delete existing value on unlink
 9         true,
10         //Get association
11         () => this._Addresses,
12         //Object matches identifier
13         (address, identifier) => string.Compare(identifier, address.Name, true) == 0,
14         //Set object identifier
15         (address, identifier) => address.Name = identifier);
16     return postalAddresses;
17   }
18 }
19

You might want to make the setter for the indexed property (Address.Name in this case) to internal so that only business classes can alter it. The generic code to implement this identified association is as follows

 1   public class IdentifiedAssociation<TIdentifier, TAssociated> : IEnumerable<TAssociated>
 2     where TAssociated : IEcoObject
 3   {
 4     readonly bool DeleteOnUnlink;
 5     readonly Func<IList<TAssociated>> GetAssociation;
 6     readonly Func<TAssociated, TIdentifier, bool> ObjectMatchesIdentifier;
 7     readonly Action<TAssociated, TIdentifier> SetIdentifier;
 8 
 9     public IdentifiedAssociation(
10       bool deleteOnUnlink,
11       Func<IList<TAssociated>> getAssociation,
12       Func<TAssociated, TIdentifier, bool> objectMatchesIdentifier,
13       Action<TAssociated, TIdentifier> setIdentifier)
14     {
15       Contract.Requires(getAssociation != null);
16       Contract.Requires(objectMatchesIdentifier != null);
17       Contract.Requires(setIdentifier != null);
18 
19       DeleteOnUnlink = deleteOnUnlink;
20 
21       GetAssociation = getAssociation;
22       ObjectMatchesIdentifier = objectMatchesIdentifier;
23       SetIdentifier = setIdentifier;
24     }
25 
26     public TAssociated this[TIdentifier identifier]
27     {
28       get
29       {
30         return GetAssociation().SingleOrDefault(x => ObjectMatchesIdentifier(x, identifier));
31       }
32       set
33       {
34         var currentValue = this[identifier];
35         if (currentValue != null && currentValue.Equals(value))
36           return;
37         if (currentValue != null && DeleteOnUnlink)
38           currentValue.AsIObject().Delete();
39         if (value != null)
40         {
41           GetAssociation().Add(value);
42           SetIdentifier(value, identifier);
43         }
44       }
45     }
46 
47     public IEnumerator<TAssociated> GetEnumerator()
48     {
49       return GetAssociation().GetEnumerator();
50     }
51 
52     System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
53     {
54       return GetEnumerator();
55     }
56   }
57

A WebServer for MonoTouch that also parses posted form data (HttpListenerRequest)

Peter Morris — Sat, 02 Apr 2011 17:58:14 GMT

I found a few examples of web servers for MonoTouch but none of them parsed the data sent in a POST request. I looked around the web and was unable to find any examples of how to achieve this. So now that I’ve written it myself I’ve decided to share my own implementation. This includes not only the code for processing the form post data but also for registering request handlers etc.

Here is an example of how you would use the web server

 1     public BookUploadViewController() 
 2       : base("BookUploadViewController", null)
 3     {
 4       RequestHandler = new DefaultRequestHandler();
 5       var defaultActionHandlerFactory = new DefaultActionHandlerFactory();
 6       RegisterActionHandlers(defaultActionHandlerFactory);
 7       RequestHandler.AddActionHandlerFactory(defaultActionHandlerFactory);
 8       
 9       WebServer = new EmbeddedWebServer(RequestHandler);
10     }
11     
12     void RegisterActionHandlers(DefaultActionHandlerFactory factory)
13     {
14       factory.RegisterHandler(
15         request => request.RawUrl == "/",
16         request => new IndexActionHandler(request)
17         );
18       factory.RegisterHandler(
19         request => 
20           string.Compare(request.RawUrl, "/Upload", true) == 0 && 
21           string.Compare(request.HttpMethod, "POST", true) == 0,
22         request => new UploadActionHandler(request)
23         );
24     }
25     
26     public override void ViewDidAppear(bool animated)
27     {
28       base.ViewDidAppear(animated);
29       StatusLabel.Text = string.Format("Server listening on\r\nhttp://{0}:8080", GetIPAddress ());
30       WebServer.Start(8080);
31     }
32     
33     public override void ViewDidDisappear (bool animated)
34     {
35       base.ViewDidDisappear(animated);
36       WebServer.Stop();
37     }
38

And here are two app specific examples of request handlers

 1 class IndexActionHandler : DefaultActionHandler
 2 {
 3   public IndexActionHandler(HttpListenerRequest request)
 4     : base(request)
 5   {
 6   }
 7   
 8   public override ActionResult Execute()
 9   {
10     var result = new HtmlResult();
11     result.AppendLine("<html>");
12     result.AppendLine("<body>");
13     result.AppendLine("<h1>Upload an image</h1>");
14     result.AppendLine("<form action='/Upload' enctype='multipart/form-data' method='post'>");
15     result.AppendLine ("<input name='Image' type='file'/><br/>");
16     result.AppendLine("<input name='Upload' type='submit' text='Upload'/>");
17     result.AppendLine("</form>");
18     result.AppendLine("</body>");
19     result.AppendLine("</html>");
20     return result;
21   }
22 }
23 
24 class UploadActionHandler : DefaultActionHandler
25 {
26   public UploadActionHandler(HttpListenerRequest request)
27     : base(request)
28   {
29   }
30 
31   public override ActionResult Execute()
32   {
33     string errorMessage = null;
34     var file = FormData.GetFile("Image");
35     if (file == null 
36       || file.FileData == null 
37       || file.FileData.Length == 0 
38       || string.IsNullOrEmpty(file.FileName))
39       errorMessage = "No image uploaded";
40     
41     if (errorMessage == null)
42       ProcessFile(file);
43       
44     var result = new HtmlResult();
45     result.AppendLine("<html>");
46     result.AppendLine("<body>");
47     if (errorMessage == null)
48       result.AppendLine("<h1>File uploaded successfully</h1>");
49     else
50     {
51       result.AppendLine("<h1>Error</h1>");
52       result.AppendLine("<h2>" + errorMessage + "</h2>");
53     }
54     result.AppendLine("</body>");
55     result.AppendLine("</html>");
56     return result;
57   }
58   
59   void ProcessFile(MultiPartStreamFileValue postedFile)
60   {
61     string fileName = "Where to save the file";
62     using (var fileStream = 
63       new FileStream(fileName, FileMode.Create, FileAccess.Write, FileShare.None))
64     {
65       fileStream.Write(postedFile.FileData, 0, postedFile.FileData.Length);
66     }
67   }
68   
69 }
70

You can download the files here.

Aurora on the iPad

Peter Morris — Mon, 14 Mar 2011 18:17:31 GMT

I fancied indulging my side interest of making music by buying some music making apps on the iPad. One of which is called "Aurora" from 4pockets.com

Because Apple don't allow trial versions of apps in the Apple store people often release a "lite" version of their app free of charge in order to let potential customers try a limited version of their app before purchasing. I was disappointed to see that this app didn't have such a version, but decided that at a price of £24 it must be pretty good so I took the plunge and bought it.

What a mistake! It is absolutely awful! Even the demo tunes (which should show it off at its best) were terrible! I looked at the Apple store to see if there is any way to get a refund, but the T&C say "all purchases are final", great!

I thought that perhaps the company that developed the app might be good with customer relations and, like myself, only want money from people who actually like my work and think it is worth paying for. Unfortunately it seems as though their philosophy is more like "We want every penny we can get our hands on, even if it means selling over priced junk to unhappy customers."

On the other hand, the very reasonably priced £5 app "MorphWhiz" is great fun!

Mr P Morris to sales
Hi

I bought aurora for my iPad. With a lack of a "lite" version I was unable to evaluate it without purchasing it. Having purchased it I have found I really isn't my cup of tea at all. Is there a way to get a refund?

Pete

sales@4pockets.com to me
Dear Sir,

You will need to talk to Apple

Regards
Bill Muir

Peter Morris to sales
Hi Bill

I've read the terms and conditions and it seems that there is no process for issuing refunds after the application has been downloaded, which is why I wrote to you directly.

Regards

Pete

sales@4pockets.com to me
Dear Sir,

Your transaction is with Apple. We get no data as to who has purchased product via Apple. We only get dates, number of sales, value and country details. Sorry we are unable to help.

Regards
Bill Muir

Peter Morris to sales
Yes, I can see that being potential for fraudulent claims :)

What if I were to send you proof of purchase when I receive my invoice, would that be sufficient?

Pete

sales@4pockets.com to me
Dear Sir,

We can not help you. You are a client of Apple not 4pockets.com

Regards
Bill Muir

Peter Morris to sales
Okay, that's a real cop-out answer. I will take this to mean "Dear sir, we intend to grab every penny we can and to hell with customer satisfaction." I shall ensure my rating on your product accurately reflects your sentiments.

Thanks for taking your share of £23 of my hard earned money for an app not worth more than £5.

Shame on you.

Pete

Additional visualisations in ECO

Peter Morris — Thu, 10 Feb 2011 11:01:33 GMT

My model needs to take snapshots of certain data and to do this I have various snapshot classes.

Sometimes you might snapshot an aggregate root such as PurchaseOrder and expect all PurchaseOrderLines to be snapshotted along with it. Sometimes though the Parent/Child relationship is not part of an aggregate root and you want the child snapshot to create the parent snapshot, for example when snapshotting an Address you might want to snapshot the Country.

So when I was looking at my snapshot diagrams it wasn't immediately obviously which behaviour you get. Hans showed me this article: http://theblog.capableobjects.com/2009/12/catching-more-information-in-your-model.html

Now I have added symbols + tagged value definitions to my model and as a consequence the diagrams show me visually which way the snapshots work. Brilliant!

How many unique pizza combinations does Domino’s Pizza have?

Peter Morris — Mon, 10 Jan 2011 11:10:01 GMT

Okay, a weird topic I know but I saw a question asked in NewScientist querying whether the Domino’s Pizza claim of 1.8 billion combinations is possible. Here is the answer I am submitting:

If we have 4 options on the menu (ABCD) and choose 1 topping we have 4 unique combinations. If however we choose 2 toppings we have 6 unique combinations. As toppings in a different order are considered the same combination this means that when choosing the second topping we must choose from a sub-set of the entire menu. For example, when working out how many combinations start with A the second selection is limited to B..D, but when working out how many start with B the second selection is limited to C..D (because BA is the same combination as AB.) Domino's where I live has a menu of 21 toppings. So the valid options for the first selection when choosing 2 toppings are 1..20 (20 because we have 1 more selection to make after this), the valid options for the second selection are (first selection + 1)..21 (21 because there are no more selections to make after this.)

Not only does Domino's have 21 toppings on their menu, but you have the option of single/double which doubles the amount of options per topping, however you are only permitted a maximum of 9 toppings per pizza which brings the number of combinations down significantly.To bring the number of unique combinations back up again we have to take into account that the customer may order between 0..9 toppings, so we have to work out the iterations for each and add them together, where zero toppings is a single choice. Finally, in addition to the toppings you can choose from 3 sauces (single/double), 2 cheeses (single/double), and from 6 bases - increasing the total combinations by 6x4x6 = 144! I do not consider pizza size a “combination”.

I'm not much of a mathematician myself so I wrote a simple piece of recursive code to work out the result, which by the way is 200,407,536 - In short, the answer is "No."

And here is the source code to work it out:

 1     void ButtonCompute_Click(object sender, EventArgs e)
 2     {
 3       long combinations = 0;
 4       for (int toppingsToAdd = 1; toppingsToAdd <= 9; toppingsToAdd++)
 5         combinations += CalculateCombinations(21, toppingsToAdd);
 6 
 7       //Add one combination for "No toppings"
 8       combinations++;
 9 
10       //Take into account the non topping variations
11       combinations = combinations
12         * 6 //Multiply by 3 sauces, single or double
13         * 4 //Multiply by 2 cheeses, single or double
14         * 6; //Multiply by 6 bases
15       
16       textBox1.Text = string.Format("Combinations: {0}", combinations);
17     }
18 
19     long CalculateCombinations(int toppingsAvailable, int toppingsToAdd)
20     {
21       if (toppingsToAdd == 1)
22         return toppingsAvailable * 2; //Single or double
23 
24       long result = 0;
25       int toppingsToAddAfterThis = toppingsToAdd - 1;
26       checked
27       {
28         for (
29           //Start at highest value, e.g. 21 options
30           int currentChoice = toppingsAvailable;
31           //Keep enough options to fulfill the rest of the choices
32           currentChoice > toppingsToAddAfterThis;
33           currentChoice--)
34           result += CalculateCombinations(currentChoice - 1, toppingsToAddAfterThis);
35       }
36       return result;
37     }
38

Creating a pooled lifetime manager for Unity

Peter Morris — Sun, 19 Dec 2010 18:33:39 GMT

My application has a child container per request, this is because there are a lot of services used in each request which depend upon an IUnitOfWork. I thought it would be nice if I could define a pool of these IUnitOfWork instances so that any cost involved in creating them is reduced, they can just be reused in a round-robin fashion. Well, more accurately, the object space (EcoSpace) on which they depend can anyway.

A pool can now be registered like so…

1 //Must be called once, when the container is created
2 container.AddNewExtension<PooledLifetimeExtension>();
3 //To register a pooled item
4 container.RegisterType
5   <
6     ISomeItemThatIsExpensiveToCreate, 
7     SomeItemThatIsExpensiveToCreate
8   >(new PooledLifetimeManager(10));

The number 10 specifies how many instances at once may be stored in the pool. If an instance requests an item from the pool when it is empty it will get a new instance, it’s only at the point where an instance is returned to the pool that the MaxPoolSize is honoured – if the pool is not full then the instance goes back into the pool, if the pool is already full then Dispose is called on it instead. Of course you should be careful when pooling that your pooled items don’t hold onto other injected references which are also pooled as that will cause problems.

I have also added the following interface so that an instance can (optionally) specify whether or not its current state should permit it to go back into the pool, and two methods which indicate to the instance when it has been retrieved from a pool or is about to be returned to the pool – in my case I deactivated the object space upon returning in order to flush any object cache, and reactivated it again when retrieved from the pool.

1 public interface IPooledResource
2 {
3   bool CanReturnToPool { get; }
4   void RetrievedFromPool();
5   void ReturningToPool();
6 }

It’s important to note that this only works with child containers. You should create your main controller as a kind of template by registering your request specific services (like IUnitOfWork) with HierarchicalLifetimeManager. The PooledLifetimeManager will work in the same way as HierarchicalLifetimeManager except for the addition of pooling, and it will automatically attempt to return items to the pool once the child container is disposed of.

  1 //PooledLifetimeExtension.cs
  2 using Microsoft.Practices.Unity;
  3 using Microsoft.Practices.Unity.ObjectBuilder;
  4 
  5 namespace YourNameHere.Infrastructure.Unity
  6 {
  7   public class PooledLifetimeExtension : UnityContainerExtension
  8   {
  9     protected override void Initialize()
 10     {
 11       // Add to type mapping stage so that it runs before the lifetime stage
 12       Context.Strategies.AddNew<PooledLifetimeStrategy>
 13         (UnityBuildStage.TypeMapping);
 14     }
 15   }
 16 }
 17 
 18 
 19 
 20 //PooledLifetimeManager.cs
 21 using System;
 22 using System.Collections.Generic;
 23 using Microsoft.Practices.Unity;
 24 using Microsoft.Practices.ObjectBuilder2;
 25 
 26 namespace YourNameHere.Infrastructure.Unity
 27 {
 28   public class PooledLifetimeManager : LifetimeManager
 29   {
 30     readonly PooledLifetimeManagerPool Pool;
 31 
 32     public PooledLifetimeManager(int maxPoolSize)
 33     {
 34       Pool = new PooledLifetimeManagerPool(maxPoolSize);
 35     }
 36 
 37     internal PooledLifetimeManagerPoolConsumer CreatePoolUserForChildContainer()
 38     {
 39       return new PooledLifetimeManagerPoolConsumer(Pool);
 40     }
 41 
 42     #region GetValue/SetValue/RemoveValue all redundant
 43     public override object GetValue()
 44     {
 45       throw new InvalidOperationException();
 46     }
 47 
 48     public override void SetValue(object newValue)
 49     {
 50       throw new InvalidOperationException();
 51     }
 52 
 53     public override void RemoveValue()
 54     {
 55       throw new InvalidOperationException();
 56     }
 57     #endregion
 58   }
 59 
 60   internal class PooledLifetimeManagerPool
 61   {
 62     readonly int MaxPoolSize;
 63     readonly object SyncRoot = new object();
 64     readonly Queue<object> Queue = new Queue<object>();
 65 
 66     public PooledLifetimeManagerPool(int maxPoolSize)
 67     {
 68       if (maxPoolSize < 0)
 69         throw new ArgumentOutOfRangeException(
 70           "MaxPoolSize", "Cannot be less than zero");
 71       MaxPoolSize = maxPoolSize;
 72     }
 73 
 74     internal object RetrieveFromPool()
 75     {
 76       object result = null;
 77       lock (SyncRoot)
 78         if (Queue.Count > 0)
 79           result = Queue.Dequeue();
 80       IPooledResource resultAsIPooledResource = result as IPooledResource;
 81       if (resultAsIPooledResource != null)
 82         resultAsIPooledResource.RetrievedFromPool();
 83       return result;
 84     }
 85 
 86     internal void ReturnToPool(object instance)
 87     {
 88       if (instance == null)
 89         throw new ArgumentNullException("Instance");
 90       IPooledResource instanceAsIPooledResource = instance as IPooledResource;
 91       if (instanceAsIPooledResource != null)
 92       {
 93         if (!instanceAsIPooledResource.CanReturnToPool)
 94           return;
 95         instanceAsIPooledResource.ReturningToPool();
 96       }
 97       bool wentIntoPool = false;
 98       lock (SyncRoot)
 99         if (Queue.Count < MaxPoolSize)
100         {
101           Queue.Enqueue(instance);
102           wentIntoPool = true;
103         }
104 
105       //Dispose any instances which did not go back into the pool
106       if (!wentIntoPool && instance is IDisposable)
107         ((IDisposable)instance).Dispose();
108     }
109   }
110 
111   public class PooledLifetimeManagerPoolConsumer :
112     ContainerControlledLifetimeManager, IDisposable
113   {
114     readonly PooledLifetimeManagerPool SharedPool;
115     object Instance;
116 
117     internal PooledLifetimeManagerPoolConsumer(
118       PooledLifetimeManagerPool sharedPool)
119     {
120       if (sharedPool == null)
121         throw new ArgumentNullException("SharedPool");
122       SharedPool = sharedPool;
123     }
124 
125     protected override object SynchronizedGetValue()
126     {
127       if (Instance == null)
128         Instance = SharedPool.RetrieveFromPool();
129       return Instance;
130     }
131 
132     protected override void SynchronizedSetValue(object newValue)
133     {
134       if (Instance != null && newValue == null)
135         SharedPool.ReturnToPool(Instance);
136       Instance = newValue;
137     }
138 
139     public override void RemoveValue()
140     {
141       throw new InvalidOperationException();
142     }
143 
144     void IDisposable.Dispose()
145     {
146       SetValue(null);
147       base.Dispose();
148     }
149   }
150 }
151 
152 
153 
154 //PooledLifetimeStrategy.cs
155 using Microsoft.Practices.ObjectBuilder2;
156 
157 namespace YourNameHere.Infrastructure.Unity
158 {
159   public class PooledLifetimeStrategy : BuilderStrategy
160   {
161     public override void PreBuildUp(IBuilderContext context)
162     {
163       PooledLifetimeManager activeLifetime = 
164         context.PersistentPolicies.Get<ILifetimePolicy>(context.BuildKey)
165           as PooledLifetimeManager;
166       if (activeLifetime != null)
167       {
168         // did this come from the local container or the parent?
169         var localLifetime = 
170           context.PersistentPolicies.Get<ILifetimePolicy>(
171             context.BuildKey, true);
172         if (localLifetime == null)
173         {
174           // came from parent, add a ContainerControlledLifetime here
175           var newLifeTime = activeLifetime.CreatePoolUserForChildContainer();
176           context.PersistentPolicies.Set<ILifetimePolicy>(
177             newLifeTime, context.BuildKey);
178           //Make sure it gets disposed
179           //so that it can return its reference to the pool
180           context.Lifetime.Add(newLifeTime);
181         }
182       }
183     }
184   }
185 }
186 
187 
188 
189 //PooledResourceIntf.cs
190 namespace YourNameHere.Infrastructure.Unity
191 {
192   public interface IPooledResource
193   {
194     bool CanReturnToPool { get; }
195     void RetrievedFromPool();
196     void ReturningToPool();
197   }
198 }
199

Unity child containers + ASP MVC = Memory leak

Peter Morris — Sun, 19 Dec 2010 13:33:35 GMT

I was making some speed improvements to my current ASP MVC application. One of the things I did was to change from creating a completely new IUnityContainer for each request over to creating one master (template) container with all the services registered with HierarchicalLifetimeManager. Then whenever a controller is required my ControllerFactory does this

1 if (controllerType == null)
2   return null;
3 var requestContainer = Container.CreateChildContainer();
4 return (IController) requestContainer.Resolve(controllerType);

That’s all nice and simple, however it causes a memory leak. The reason is that the parent container holds a reference to all of its children. The only way to resolve this is to Dispose of the child container. Now obviously we cannot dispose of it in the controller factory because we need to return a fully working Controller. So the next thing I tried was to dispose of the request container in IControllerFactory.ReleaseController. The problem with this is that the controller is released before the view is rendered, so if your view depends on objects which retrieve their state from some kind of object space then this is too soon to dispose of the request container. So ultimately I couldn’t find anywhere in the ASP MVC framework into which I could hook an event which gets fired after the request has finished.

To solve the problem my IControllerFactory no longer returns the controller type requested. Instead at runtime it creates a descendant class which implements IController directly and then passes the request on to the original controller class. The type returned stores a reference to the per-request IUnityContainer and then does this

 1 void IController.Execute(RequestContext context)
 2 {
 3   try
 4   {
 5     base.Execute(context);
 6   }
 7   finally
 8   {
 9     RequestUnityContainer.Dispose();
10   }
11 }

So now we have a bit of code in our controller which disposes of the per-request unity container after the entire request has been processed. The ControllerFactory code only needs to be changed like so

1 protected override IController GetControllerInstance(RequestContext requestContext, Type controllerType)
2 {
3   if (controllerType == null)
4     return null;
5   IUnityContainer requestContainer = Container.CreateChildContainer();
6   ControllerBase controller = ContainerDisposingControllerFactory.Create(requestContainer, controllerType);
7   return controller;
8 }

The code required is listed below…

  1 //ContainerDisposingControllerIntf.cs
  2 using Microsoft.Practices.Unity;
  3 
  4 namespace YourNameHere.Infrastructure.Web
  5 {
  6   public interface IContainerDisposingController
  7   {
  8     IUnityContainer IContainerDisposingController_UnityContainer { get; set; }
  9   }
 10 }
 11 
 12 
 13 //ContainerDisposingControllerFactory.cs
 14 using System;
 15 using System.Collections.Generic;
 16 using System.Linq;
 17 using System.Reflection;
 18 using System.Reflection.Emit;
 19 using System.Threading;
 20 using System.Web.Mvc;
 21 using Microsoft.Practices.Unity;
 22 
 23 namespace YourNameHere.Infrastructure.Web
 24 {
 25   public static class ContainerDisposingControllerFactory
 26   {
 27     const string UnityContainerBackingFieldName = "IContainerDisposingController_BackingField";
 28     static MethodInfo DisposeMethodInfo = typeof(IDisposable).GetMethod("Dispose");
 29     static readonly Dictionary<Type, Type> InterceptingType_BySuperClass = new Dictionary<Type, Type>();
 30     static ReaderWriterLockSlim Locker = new ReaderWriterLockSlim();
 31 
 32     public static ControllerBase Create(IUnityContainer containerToDispose, Type controllerType)
 33     {
 34       try
 35       {
 36         return CreateTypeAndInstance(containerToDispose, controllerType);
 37       }
 38       catch
 39       {
 40         containerToDispose.Dispose();
 41         throw;
 42       }
 43     }
 44 
 45     private static ControllerBase CreateTypeAndInstance(IUnityContainer containerToDispose, Type controllerType)
 46     {
 47       Type interceptingControllerType;
 48       Locker.EnterUpgradeableReadLock();
 49       try
 50       {
 51         if (!InterceptingType_BySuperClass.TryGetValue(controllerType, out interceptingControllerType))
 52         {
 53           Locker.EnterWriteLock();
 54           try
 55           {
 56             interceptingControllerType = CreateInterceptingControllerType(controllerType);
 57             InterceptingType_BySuperClass[controllerType] = interceptingControllerType;
 58           }
 59           finally
 60           {
 61             Locker.ExitWriteLock();
 62           }
 63         }
 64       }
 65       finally
 66       {
 67         Locker.ExitUpgradeableReadLock();
 68       }
 69 
 70       var result = (Controller)containerToDispose.Resolve(interceptingControllerType);
 71       var resultAsIUnityContainerController = (IContainerDisposingController)result;
 72       resultAsIUnityContainerController.IContainerDisposingController_UnityContainer = containerToDispose;
 73       return result;
 74     }
 75 
 76     static Type CreateInterceptingControllerType(Type controllerType)
 77     {
 78       if (!typeof(ControllerBase).IsAssignableFrom(controllerType))
 79         throw new ArgumentException("ControllerType does not descend from ControllerBase");
 80 
 81       string guid = Guid.NewGuid().ToString();
 82       var assemblyName = new AssemblyName(guid);
 83       var assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(
 84         assemblyName,
 85         AssemblyBuilderAccess.Run);
 86       var moduleBuilder = assemblyBuilder.DefineDynamicModule(guid);
 87       var typeBuilder = moduleBuilder.DefineType(
 88         guid,
 89         TypeAttributes.Class | TypeAttributes.Public,
 90         controllerType);
 91       CreateConstructor(controllerType, typeBuilder);
 92       FieldBuilder unityContainerBackingFieldBuilder;
 93       ImplementIContainerDisposingController(typeBuilder, out unityContainerBackingFieldBuilder);
 94       ImplementIController(controllerType, typeBuilder, unityContainerBackingFieldBuilder);
 95       return typeBuilder.CreateType();
 96     }
 97 
 98     static void CreateConstructor(Type controllerType, TypeBuilder typeBuilder)
 99     {
100       var constructorInfo = controllerType.GetConstructors()
101         .OrderByDescending(x => x.GetParameters().Count())
102         .FirstOrDefault();
103       if (constructorInfo == null)
104         return;
105       ParameterInfo[] constructorParameters =
106         constructorInfo.GetParameters().ToArray();
107       Type[] parameterTypes = constructorParameters.Select(x => x.ParameterType).ToArray();
108 
109       var constructorBuilder = typeBuilder.DefineConstructor(
110         MethodAttributes.Public,
111         CallingConventions.Standard,
112         parameterTypes);
113 
114       //Define the parameters for our new constructor
115       for (int argumentIndex = 0; argumentIndex < parameterTypes.Length; argumentIndex++)
116         constructorBuilder.DefineParameter(
117           argumentIndex + 1,
118           constructorParameters[argumentIndex].Attributes,
119           constructorParameters[argumentIndex].Name);
120 
121       var bodyGenerator = constructorBuilder.GetILGenerator();
122       bodyGenerator.Emit(OpCodes.Ldarg_0);
123       for (int argumentIndex = 0; argumentIndex < parameterTypes.Length; argumentIndex++)
124         bodyGenerator.Emit(OpCodes.Ldarg_S, argumentIndex + 1);
125       bodyGenerator.Emit(OpCodes.Call, constructorInfo);
126       bodyGenerator.Emit(OpCodes.Ret);
127     }
128 
129     static void ImplementIContainerDisposingController(TypeBuilder typeBuilder, out FieldBuilder unityContainerBackingFieldBuilder)
130     {
131       typeBuilder.AddInterfaceImplementation(typeof(IContainerDisposingController));
132       unityContainerBackingFieldBuilder = typeBuilder.DefineField(
133         UnityContainerBackingFieldName,
134         typeof(IUnityContainer),
135         FieldAttributes.Private);
136 
137       var propertyAccessorAttributes =
138         MethodAttributes.Public | MethodAttributes.SpecialName |
139         MethodAttributes.HideBySig | MethodAttributes.Virtual;
140 
141       var getterBuilder = typeBuilder.DefineMethod(
142         "get_IContainerDisposingController_UnityContainer",
143         propertyAccessorAttributes,
144         typeof(IUnityContainer),
145         Type.EmptyTypes);
146       var getterGenerator = getterBuilder.GetILGenerator();
147       getterGenerator.Emit(OpCodes.Ldarg_0);
148       getterGenerator.Emit(OpCodes.Ldfld, unityContainerBackingFieldBuilder);
149       getterGenerator.Emit(OpCodes.Ret);
150 
151       var setterBuilder = typeBuilder.DefineMethod(
152         "set_IContainerDisposingController_UnityContainer",
153         propertyAccessorAttributes,
154         null,
155         new Type[] { typeof(IUnityContainer) });
156       var setterGenerator = setterBuilder.GetILGenerator();
157       setterGenerator.Emit(OpCodes.Ldarg_0);
158       setterGenerator.Emit(OpCodes.Ldarg_1);
159       setterGenerator.Emit(OpCodes.Stfld, unityContainerBackingFieldBuilder);
160       setterGenerator.Emit(OpCodes.Ret);
161     }
162 
163     static void ImplementIController(Type controllerType, TypeBuilder typeBuilder, FieldBuilder unityContainerBackingFieldBuilder)
164     {
165       typeBuilder.AddInterfaceImplementation(typeof(IController));
166       MethodInfo baseMethod = null;
167       Type implementingType = controllerType;
168       do
169       {
170         baseMethod = implementingType.GetMethod(
171           "Execute",
172           BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
173         implementingType = implementingType.BaseType;
174       }
175       while (baseMethod == null && implementingType != null);
176       if (baseMethod == null)
177         throw new NotImplementedException(controllerType.Name + " does not implement IController.Execute");
178 
179       var methodParameters = baseMethod.GetParameters();
180       var methodBuilder = typeBuilder.DefineMethod(
181         typeof(IController).Name + ".Execute",
182         MethodAttributes.Public | MethodAttributes.Virtual |
183         MethodAttributes.ReuseSlot | MethodAttributes.HideBySig,
184         null,
185         methodParameters.Select(x => x.ParameterType).ToArray());
186       //Define the parameters for our new constructor
187       for (int argumentIndex = 0; argumentIndex < methodParameters.Length; argumentIndex++)
188         methodBuilder.DefineParameter(
189           argumentIndex + 1,
190           methodParameters[argumentIndex].Attributes,
191           methodParameters[argumentIndex].Name);
192 
193       var bodyGenerator = methodBuilder.GetILGenerator();
194       bodyGenerator.BeginExceptionBlock();
195       bodyGenerator.Emit(OpCodes.Ldarg_0);
196       for (int argumentIndex = 0; argumentIndex < methodParameters.Length; argumentIndex++)
197         bodyGenerator.Emit(OpCodes.Ldarg_S, argumentIndex + 1);
198       bodyGenerator.Emit(OpCodes.Call, baseMethod);
199       bodyGenerator.BeginFinallyBlock();
200       bodyGenerator.Emit(OpCodes.Ldarg_0);
201       bodyGenerator.Emit(OpCodes.Ldfld, unityContainerBackingFieldBuilder);
202       bodyGenerator.Emit(OpCodes.Call, DisposeMethodInfo);
203       bodyGenerator.EndExceptionBlock();
204       bodyGenerator.Emit(OpCodes.Ret);
205       typeBuilder.DefineMethodOverride(methodBuilder, baseMethod);
206     }
207   }
208 }

ECO atomic operations

Peter Morris — Tue, 30 Nov 2010 20:40:07 GMT

I’ve just created a simple class which I thought I’d share.

  Account1.Balance += 10;
  Account2.Balance -= 10;

In this case we might expect the second line to throw an exception if the adjustment is not permitted, but the first line has already executed. Obviously this isn’t a problem because we simply wouldn’t update the database, but sometimes you want an operation to occur in memory as an atomic operation; like this

using (var atomicOperation = new AtomicOperation(EcoSpace))
{
  Account1.Balance += 10;
  Account2.Balance -= 10;
  atomicOperation.Commit();
}

And so that is exactly what I wrote. The class uses the UndoService to create/merge/remove undo blocks so it is even possible to nest atomic operations.

public class AtomicOperation : IDisposable
{
  IUndoService UndoService;
  bool IsResolved;
  string UndoBlockName;

  public AtomicOperation(IUnitOfWork unitOfWork)
  {
    Contract.Requires(unitOfWork != null);
    Contract.Requires(unitOfWork.ObjectSpace != null);

    UndoBlockName = Guid.NewGuid().ToString();
    UndoService = unitOfWork.ObjectSpace.GetEcoService<IUndoService>();
    UndoService.StartUndoBlock(UndoBlockName);
  }

  public void Commit()
  {
    if (IsResolved)
      throw new InvalidOperationException("AtomicOperation has already been committed or rolled back");

    IsResolved = true;
    int index = UndoService.UndoList.IndexOf(UndoBlockName);
    if (index > 0)
    {
      string nameOfBlockAbove = UndoService.UndoList[index - 1].Name;
      UndoService.UndoList.MergeBlocks(nameOfBlockAbove, UndoBlockName);
    }
    else
    {
      if (index > 0)
        UndoService.UndoList.RemoveBlock(UndoBlockName);
      if (UndoService.RedoList.IndexOf(UndoBlockName) > 0)
        UndoService.RedoList.RemoveBlock(UndoBlockName);
    }
  }

  public void Rollback()
  {
    if (IsResolved)
      throw new InvalidOperationException("AtomicOperation has already been committed or rolled back");

    IsResolved = true;
    if (UndoService.UndoList.IndexOf(UndoBlockName) > -1)
      UndoService.UndoBlock(UndoBlockName);
    if (UndoService.RedoList.IndexOf(UndoBlockName) > -1)
      UndoService.RedoList.RemoveBlock(UndoBlockName);
  }

  void IDisposable.Dispose()
  {
    GC.SuppressFinalize(this);
    if (!IsResolved)
      Rollback();
  }

  ~AtomicOperation()
  {
    throw new InvalidOperationException("AtomicOperation was not disposed, try using()");
  }
}

ASP MVC CheckListBox

Peter Morris — Fri, 26 Nov 2010 14:56:46 GMT

I needed to present the user with a list of objects from which they could select multiple items. There is a MultiSelectList class in ASP MVC so I looked into how to use that. It would seem that to use this class we need to use Html.ListBox. I think this is a poor choice because it requires the user to hold down the Control key to select additional options, and it is too easy to deselect all of your values accidentally by clicking the control accidentally without the Control key held down.

What I really wanted was something like a CheckListBox, a list of items with a check box next to them, so that’s what I have implemented. Here is an example of how to set up the view data for my CheckListBox extension.

  public ActionResult Index()
  {
    var availableItems = new List<MyItem>();
    availableItems.Add(new MyItem("A", "One"));
    availableItems.Add(new MyItem("B", "Two"));
    availableItems.Add(new MyItem("C", "Three"));
    availableItems.Add(new MyItem("D", "Four"));
    var selectedItems = availableItems.Skip(1).Take(2);
    ViewData["Items"] = CheckListBoxItems.Create(
      availableItems, 
      x => x.Code, 
      x => x.Name, 
      x => selectedItems.Contains(x));
    return View();
  }

  [HttpPost]
  public ActionResult Index(CheckListBoxItems items)
  {
    return Index();
  }

Make sure that when your application starts you register the custom binder for CheckListBoxItems

protected void Application_Start()
{
  ...
  ModelBinders.Binders.Add(
    typeof(CheckListBoxItems),
    new CheckListBoxItemsModelBinder());
}

Here is the first example of how you can mark up your view html.

<%: Html.CheckListBox("Items", (CheckListBoxItems)ViewData["Items"]) %>
<!-- Outputs the following HTML
<input type="hidden" name="Items[A].Key" value="A"/>
<input type="checkbox" name="Items[A].Selected" value="true"  />&nbsp;One<br/>
<input type="hidden" name="Items[B].Key" value="B"/>
<input type="checkbox" name="Items[B].Selected" value="true" checked />&nbsp;Two<br/>
<input type="hidden" name="Items[C].Key" value="C"/>
<input type="checkbox" name="Items[C].Selected" value="true" checked />&nbsp;Three<br/>
<input type="hidden" name="Items[D].Key" value="D"/>
<input type="checkbox" name="Items[D].Selected" value="true"  />&nbsp;Four<br/>
-->

And here is another example where you can pass in the HTML to use for each item in the list. The HTML is just a string used in String.Format where {0} is the check box html and {1} is where the text will be displayed. In the following example I pass the parameters in in the order 1,0 because I want the text first followed by the check box control.

<table>
  <tr>
    <th>Item</th>
    <th>Selected</th>
  </tr>
  <%: Html.CheckListBox(
    "Items", 
    (CheckListBoxItems)ViewData["Items"], 
    "<tr><td>{1}</td><td>{0}</td></tr>") %>
</table>
<!-- Outputs the following HTML
<table>
  <tr>
    <th>Item</th>
    <th>Selected</th>
  </tr>
  <tr>
    <td>One</td>
    <td>
      <input type="hidden" name="Items[A].Key" value="A"/>
      <input type="checkbox" name="Items[A].Selected" value="true"  />
    </td>
  </tr>
  <tr>
    <td>Two</td>
    <td>
      <input type="hidden" name="Items[B].Key" value="B"/>
      <input type="checkbox" name="Items[B].Selected" value="true" checked />
    </td>
  </tr>
  <tr>
    <td>Three</td>
    <td>
      <input type="hidden" name="Items[C].Key" value="C"/>
      <input type="checkbox" name="Items[C].Selected" value="true" checked />
    </td>
  </tr>
  <tr>
    <td>Four</td>
    <td>
      <input type="hidden" name="Items[D].Key" value="D"/>
      <input type="checkbox" name="Items[D].Selected" value="true"  />
    </td>
  </tr>
</table>
-->

Here is the source code:

//CheckListBoxItem.cs
using System.Collections.Generic;

namespace System.Web.Mvc
{
  public class CheckListBoxItem
  {
    public string Key { get; set; }
    public string Text { get; set; }
    public bool Selected { get; set; }
  }

  public class CheckListBoxItems : List<CheckListBoxItem>
  {
    public static CheckListBoxItems Create<T>(
      IEnumerable<T> source,
      Func<T, string> key,
      Func<T, string> text,
      Func<T, bool> selected)
    {
      var result = new CheckListBoxItems();
      foreach (T item in source)
      {
        CheckListBoxItem newItem = new CheckListBoxItem();
        result.Add(newItem);
        newItem.Key = key(item);
        newItem.Text = text(item);
        newItem.Selected = selected(item);
      }
      return result;
    }
  }
}

//CheckListBoxItems.cs
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace System.Web.Mvc.Html
{
  public static class CheckListBoxExtensions
  {
    public static MvcHtmlString CheckListBox(this HtmlHelper htmlHelper, string name, IEnumerable<CheckListBoxItem> items)
    {
      return htmlHelper.CheckListBox(name, items, "{0}&nbsp;{1}<br/>");
    }

    public static MvcHtmlString CheckListBox(this HtmlHelper htmlHelper, string name, IEnumerable<CheckListBoxItem> items, string itemFormat)
    {
      name = htmlHelper.Encode(name);
      var resultBuilder = new StringBuilder();
      var itemList = items.ToList();
      for (int index = 0; index < itemList.Count; index++)
      {
        CheckListBoxItem item = itemList[index];
        string encodedKey = htmlHelper.Encode(item.Key);
        string encodedText = htmlHelper.Encode(item.Text);
        string keyHtml =
          string.Format("<input type=\"hidden\" name=\"{0}[{1}].Key\" value=\"{2}\"/>", name, encodedKey, encodedKey);
        string checkBoxHtml =
          string.Format(
            "<input type=\"checkbox\" name=\"{0}[{1}].Selected\" value=\"true\" {2} />",
            name, encodedKey, item.Selected ? "checked" : "");
        resultBuilder.AppendFormat(itemFormat, keyHtml + checkBoxHtml, encodedText);
      }
      return MvcHtmlString.Create(resultBuilder.ToString());
    }
  }
}

//CheckListBoxItemsModelBinder.cs
using System.Linq;
using System.Text.RegularExpressions;

namespace System.Web.Mvc
{
  public class CheckListBoxItemsModelBinder : IModelBinder
  {
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
      var result = new CheckListBoxItems();
      string modelName = bindingContext.ModelName;
      string regexKeyPattern = "^" + modelName + @"\[.+?\]\.Key$";
      var keyRegex = new Regex(regexKeyPattern, RegexOptions.IgnoreCase);
      var keys = controllerContext.RequestContext.HttpContext.Request.Form.AllKeys.Where(x => keyRegex.IsMatch(x));
      foreach (string key in keys)
      {
        var valueSubmittedForKey = bindingContext.ValueProvider.GetValue(key);
        bindingContext.ModelState.SetModelValue(key, valueSubmittedForKey);

        string valueKey = key.Substring(0, key.Length - 4) + ".Selected";
        var valueSubmittedForValueKey = bindingContext.ValueProvider.GetValue(valueKey);
        bindingContext.ModelState.SetModelValue(valueKey, valueSubmittedForValueKey);

        var checkListBoxItem = new CheckListBoxItem();
        result.Add(checkListBoxItem);
        checkListBoxItem.Key = valueSubmittedForKey.AttemptedValue;
        checkListBoxItem.Selected = valueSubmittedForValueKey != null;
      }
      return result;
    }
  }
}