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 Wednesday, May 25, 2016

The CSLA PCL that supports Xamarin includes an implementation of System.ComponentModel.DataAnnotations, and that includes numerous types, one of which is DisplayAttribute.

The PCL uses type forwarding so at runtime the platform's DataAnnotations implementation is used (if available), and the CSLA implementation is only used at runtime for platforms where there's not already an implementation (WinRT Phone is the only remaining platform afaik).

There is a problem with Xamarin however, where all types seem to forward and work fine except for DisplayAttribute. The problem in this case is that at runtime it seems that mono is unable to locate the correct ctor for the type:

"System.MissingMethodException: Method 'DisplayAttribute..ctor' not found.\n  at (wrapper managed-to-native) System.MonoCustomAttrs:GetCustomAttributesInternal (System.Reflection.ICustomAttributeProvider,System.Type,bool)\n  at System.MonoCustomAttrs.GetCustomAttributesBase (ICustomAttributeProvider obj, System.Type attributeType, Boolean inheritedOnly) [0x00019] in /Users/builder/data/lanes/3236/ee215fc9/source/mono/mcs/class/corlib/System/MonoCustomAttrs.cs:128 \n  at System.MonoCustomAttrs.GetCustomAttributes (ICustomAttributeProvider obj, System.Type attributeType, Boolean inherit) [0x00040] in /Users/builder/data/lanes/3236/ee215fc9/source/mono/mcs/class/corlib/System/MonoCustomAttrs.cs:158 \n  at System.Reflection.MonoProperty.GetCustomAttributes (System.Type attributeType, Boolean inherit) [0x00000] in /Users/builder/data/lanes/3236/ee215fc9/source/mono/mcs/class/corlib/System.Reflection/MonoProperty.cs:317 \n  at Csla.Core.FieldManager.DefaultPropertyInfoFactory.GetFriendlyNameFromAttributes (System.Ty
pe type, System.String name) [0x00011] in <filename unknown>:0 \n  at Csla.Core.FieldManager.DefaultPropertyInfoFactory.Create[T] (System.Type containingType, System.String name) [0x00000] in <filename unknown>:0 \n  at Csla.ReadOnlyBase`1[T].RegisterProperty[P] (System.Linq.Expressions.Expression`1 propertyLambdaExpression) [0x0001c] in <filename unknown>:0 \n  at ProjectTracker.Library.ProjectInfo..cctor () [0x00000] in G:\\src\\rdl\\csla\\Samples\\ProjectTracker\\ProjectTracker.BusinessLibrary.Shared\\ProjectInfo.cs:10 "

This exception occurs when the consume app attempts to access the DisplayAttribute associated with a property to retrieve values from the attribute. It appears that mono is unable to create an instance of the attribute object because it can't find the ctor. The DisplayAttribute class has only a default ctor, but is typically initialized using named parameters, such as:

[Display(Name = "foo")]

I don't know what kind of ctor mono is looking for when it fails, but it obviously isn't finding the default ctor and then setting the property value, which is what would be the expected behavior.

I’m tracking this issue in the CSLA GitHub repo:

Steps to reproduce issue

The CSLA ProjectTracker reference app in my fork includes a repro of this issue. To see the issue, do the following:

  1. Clone my fork of CSLA from
  2. Checkout the 505-xamarin branch:
  3. Open the \Samples\ProjectTracker\ProjectTracker.sln solution
  4. Build the solution – it’ll pull down the CSLA .NET framework from NuGet
  5. Set a breakpoint in the XamarinFormsUi.ViewModels.ProjectList class as shown here
  6. Set the startup app to ProjectTracker.Ui.Xamarin.Droid
  7. Run the app in debug mode (on an emulator or device)
  8. On the first screen click the All Projects button

That’ll attempt to load the ProjectList page and ProjectList viewmodel. At this point the exception will occur and you’ll end up on the breakpoint because of the failure to create an instance of ProjectInfo, but that fails because mono can’t create an instance of DisplayAttribute (used on some properties in the ProjectInfo class).

Wednesday, May 25, 2016 12:51:26 PM (Central Standard Time, UTC-06:00)  #    Disclaimer
 Friday, May 20, 2016

I might have found a bug in mono, but want to see if anyone thinks I'm missing something.

The CSLA .NET framework has long included an implementation of the System.ComponentModel.DataAnnotations namespace for platforms where Microsoft/Xamarin didn’t provide that functionality. These days I think that is only Windows Phone 8.1, but that includes PCL Profile111 (which is what Xamarin currently targets as well).

Of course the CSLA implementation includes the DisplayAttribute class, which is used to decorate properties in consuming classes like this:

[Display(Name = "blah")]

That "blah" value is a human readable name/label for a property.

Because mono actually provides a System.ComponentModel.DataAnnotations implementation, my PCL uses type forwarding so at runtime the PCL implementation is ignored in favor of the platform-specific implementation provided by mono. For example:

[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.ComponentModel.DataAnnotations.DisplayAttribute))]

This works great on all platforms - except Xamarin Android/iOS where mono throws an exception because it can't find a matching constructor.

The thing is that the DisplayAttribute class has only the default constructor. The syntax being used to set the Name property of the attribute is supposed to use the default ctor, and then the Name property is explicitly set. This is a relatively old feature of C# - but I kind of suspect mono has a bug around this area, as it seems to be looking for a ctor that accepts a parameter when it should use the default ctor.

Friday, May 20, 2016 3:40:28 PM (Central Standard Time, UTC-06:00)  #    Disclaimer
 Saturday, March 26, 2011

There is now an alpha release of CSLA 4 version 4.2 available for download:

The big initiative for version 4.2 is to add support for the following platforms:

  • Linux and OS X (via Mono)
  • Android (via MonoDroid)
  • iPhone and iPad (via MonoTouch)

This alpha release does not include binaries for these platforms, but does include code and sln files (for Visual Studio and/or MonoDevelop) you can use to build the source on each of the platforms.

At this point in time we have the following:

  1. CSLA 4 builds and runs on mono in Windows and Linux.
    1. Core CSLA 4 functionality (Csla.dll) should be the same as on .NET 4.
    2. ASP.NET code using CSLA objects should work using Csla.Web.dll
    3. The Windows Forms support with Csla.Windows.dll is limited due to incompatibilities in data binding between real Windows Forms and the mono implementation of Windows Forms.
  2. CSLA 4 builds and runs on Android. Use the MonoDroid tools in Visual Studio to build Csla.dll.
    1. You should find behaviors and features for Android identical to that provided for WP7.
    2. There is not currently an equivalent to Csla.Xaml.dll for Android.
    3. No testing has been done around the use of any remote data portal channel – only the local data portal has had any testing.
  3. CSLA 4 builds and runs on iOS (iPhone/iPad). Use MonoDevelop on OS X to build Csla.dll.
    1. You should find behaviors and features for iOS identical to that provided for WP7.
    2. There is not currently an equivalent to Csla.Xaml.dll for iOS.
    3. No testing has been done around the use of any remote data portal channel – only the local data portal has had any testing.

Please remember, this is an alpha release, in the early stages of testing and stabilization. Any help you can provide in terms of testing and resolving issues is appreciated! Direct inquiries to

Other changes of note to existing .NET, SL, or WP7 users include:

  • When an async rule completes, rules for affected properties are now also run
  • BackgroundWorker from Csla.Threading is now available in WP7
  • Some cleanup work was done around CslaIdentity – this shouldn’t be a breaking change, but the internals are now quite different
  • Fix a bug in non-generic GetProperty where field wasn’t always set to the correct default value
Saturday, March 26, 2011 5:13:06 PM (Central Standard Time, UTC-06:00)  #    Disclaimer
 Wednesday, March 09, 2011

A few weeks ago I posted about my initial efforts to port CSLA 4 to MonoDroid. The idea being that business classes created for WP7 could be used on Android as well.

That inspired some people – which is awesome!

  • Stuart Bale volunteered to help port CSLA 4 to MonoTouch, for iOS (iPhone/iPad).
  • Jonny Bekkum (a long-time CSLA team member) volunteered to port CSLA 4 to mono – the open source implementation of .NET that runs on Linux, Windows, and other platforms.
  • Kevin Ford volunteered to finish what I’d started by getting CSLA 4 ported to MonoDroid (in reality, he’d already started a parallel effort, and then merged his work into mine).

Initial code for all three projects has been checked into the svn code repository. Jonny has some test apps running in mono, so there’s some confidence in that code. Kevin has a small test app running in Android, so there’s some confidence there too (though it is earlier in the process). The MonoTouch port is the hardest of the three due to some limitations of MonoTouch, and we don’t know for sure that the current code works (though it does build in MonoDevelop).

My current plan is that CSLA 4 version 4.2 will be the release that includes support for mono, Android, and iOS – in addition to the existing support for .NET, Silverlight, and Windows Phone. That’ll be exciting!

If you are a developer on any of these three new targets, we’d appreciate any help in testing the code to see if it works, and to find solutions to anything that doesn’t work. Please post any issues or comments on the forum at – thanks!

Wednesday, March 09, 2011 5:16:38 PM (Central Standard Time, UTC-06:00)  #    Disclaimer
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