Known Issues for Visual Studio 2010 Release Candidate

This post provides information on a few high profile Visual Studio 2010 Release Candidate bugs and some additional information that will help developers have a successful experience with the WPF & Silverlight Designer.

Known Issues

Visual Studio crashes when IntelliSense displays

Problem: Users have reported frequent crashes of Visual Studio 2010 Release Candidate when IntelliSense displays.  This can happen in the XAML Editor or Code Editor.

Solution: If you are experiencing crashes please install this Hot Fix:

Find in Files is very slow when the XAML Editor is open

Problem: Some customers have reported that the Find if Files feature of Visual Studio can by very slow if a XAML Editor document is open and the search is conducted shortly after opening the solution.

Solution: If this bug affects your work, close all Visual Studio documents and then close Visual Studio. Reopen Visual Studio and the solution you were working on. Before opening any documents, perform the Find in Files search.

This bug will be corrected for the final release of Visual Studio 2010.

Implicit Style using BasedOn Disables the Designer

Problem: If you have an implicit Style that uses BaseOn that is located in App.xaml or in a Merged Resource Dictionary that is merged in App.xaml, the WPF & Silverlight Designer will always be in a read-only error state.

Gold Bar Error: InstanceBuilderException was thrown due to a document error: a loop was detected in the property expressions

Error List Error: A loop was detected in the property expressions


  • Use full XAML View or edit XAML files with the Source Code (Text Editor) rather than use the Designer.
  • Instead of merging resource dictionaries in App.xaml, merge them in the root Window or root UserControl as below.  The below solution while less than ideal, will enable using the Designer along with BaseOn styles in Resource Dictionaries.

Dictionary1.xaml content – note BaseOn Style

<ResourceDictionary xmlns=""

    <Style TargetType="{x:Type TextBlock}" BasedOn="{StaticResource {x:Type TextBlock}}">
        <Setter Property="VerticalAlignment" Value="Center" />
        <Setter Property="Background" Value="Green" />
        <Setter Property="Foreground" Value="Yellow" />


MainWindow.xaml – note Dictionary1.xaml was merged here, rather than App.xaml.

<Window x:Class="MainWindow"
    Title="MainWindow" Height="350" Width="525" xmlns:my="clr-namespace:WpfApplication1">
                <ResourceDictionary Source="Dictionary1.xaml" />
        <TextBlock Text="Hello" />

Application Compatibility

Silverlight Support for Visual Studio 2010 Release Candidate

Silverlight 3 projects are supported with the Visual Studio 2010 Release Candidate build – however Silverlight 4 projects are not yet supported.

We will be adding Visual Studio 2010 Release Candidate support for Silverlight 4 with the next public Silverlight 4 drop.

If you are doing active Silverlight 4 development today we recommend staying with the Visual Studio 2010 Beta 2 build for now.

Tim Heuer has also blogged about this limitation here.

No Expression Blend Support for .NET 4.0 Projects

Expression Blend does not support for .NET 4.0 projects.  

Visual Studio 2010 Release Candidate customers can use Blend to target .NET 3.5 and SL3, but not .NET 4.0.

Designer Limitations

Custom MarkupExtensions should be located in a separate assembly

Developers writing their own MarkupExtensions should locate them in a separate assembly from the assembly that is consuming them for the best design support.  If located in the same assembly the following error may be displayed:

Error Message:  No constructor for type '[ClassName]' has 0 parameters

Image files with Build Action set to Content work at runtime but not at design time for Silverlight

Usually, Silverlight image files have their Build Action set to Resource.  The Silverlight run-time supports setting the Build Action to Content.  However the Designer will display the following gold bar error:

Error Message:  Project does not support paths relative to the root application directory.

Unhandled design-time exceptions in Converters and DataTemplateSelectors

At design-time, the Designer executes code in Converters and DataTemplateSelectors.  If those classes allow an unhandled exception to bubble up to the Designer, an exception will be displayed in the Designer.

Developers must ensure they code defensively to avoid this design-time problem.

Comments (13)
  1. Curt Nichols says:

    @Ed, the Blend Preview for .NET 4 crashes when trying to open projects, so at the moment "no Blend support" is quite correct for the RC.

  2. Curt Nichols says:

    (sent too soon)

    Obvious if you want to continue using the Blend preview with Beta2 just don’t install the RC. 🙂

  3. weitzhandler says:

    This bug is really nasty I have a gazillion of my custom local markup extensions, I raelly don’t want to move them to a different assembly!

  4. karl140.6 says:


    We do appologize for the inconvenience of moving the Custom MarkUpExtensions to another assembly

    This requirement will be reviewed in a future version of Visual Stuio.

    Have a nice day,

    Karl Shifflett

    Visual Studio Product Team

  5. weitzhandler says:

    Be sure that I am not going to move all my markup exts to an external assembly just because the IDE has quirks.

    Lucky me that the designer anyhow works.

    BTW, there is also a problem with converters, for example, I have a converter that converts Int values to String, the designer send in an incompatibe parameter variable (I think it was the unbeloved MS.Internal.UnsetValue something like this), and the converter throws exception.

    Now, of course you’ll say "So convert it to string", the answer is I am a lazy VB programmer, and this converter uses the CInt function so it accepts strings, ints and bigints etc (the actual result of the converter is the enum string of int value).

    Now I had to wrap it in a try, and return empty str when CInt tries to convert the goddamned UnsetValue instance, and I hate to write code that doesn’t serve my own needs.

    Anyway Karl, I love reading your blogs and your articles and I am having fun using the Mole of yours!

    It is a big honor for me to have a response from Karl Shifflett!


  6. karl140.6 says:

    Hi Shimmy,

    Sorry you are having another problem.

    With converters here is what I normally do:

    Check if the value parameter is null.  If so, return value.

    Check if the value is of the expected type.  If not, return value.

    Then cast value to the correct type and perform your logic.

    This removes the need for try/catch blocks.

    If you are working with enums it’s much easier to use the Shared methods on the Enum type.

    Check out:




    Glad you like the blog.  

    Have a super day,

    Karl Shifflett

    Visual Studio Product Team

  7. weitzhandler says:

    Oh g zuz!

    hell thawas a quick response

    I know of the above and I do use the GetName func in my converter, but since the expected type is either string, int or more, so wrapping the CInt function in a try works best for me, and since an exception is only expected at runtime I don’t mind so much (I made myself a not to remove it on release, I will maybe wrap the whole try in a #If DEBUG -try- #Else -no try-


    A good idea would be implementing (maybe it’s already implemented and I am not aware of?) System.ComponentModel.DesignerProperties.IsIndesignMode, not related to any element but to the running thread etc.

    Note, that even though I use 2010, I still use 3.5.

    Thanks a gazillion.

  8. karl140.6 says:


    Please post you converter code for me.  Let me see what you are doing.  You should not have to do any magic for converters work.

    BTW: You can use this hack if you need it, "DesignerProperties.IsIndesignMode(New DependencyObject())"

    This enables your classes to get access to this information.


    Karl Shifflett

    Visual Studio Product Team

  9. weitzhandler says:

    OMG, almost a chat…

    I haven’t your line but it loox like a very good idea.

    I think I will include such a function in my public module (yeah that’s what I like in VB, calling just a function, I told you I am a lazy VBer..).

    My converter consist of multiple enum types and is a bit complicated, I don’t find a reason to post it.

    It works just fine, as I said, I don’t mind to wrap in a try, cuz no exceptions are expected.

    I will anyway want to convert the ‘value’ param thru CInt.

    Also, I anyway use try for another cast (to control the ret type, call it managed TryCast), so I will post my code, I am sure you can enrich my knowledge with tips, and I always love to learn, especially when it’s from people like you.

    So here it is:

    If value Is Nothing OrElse parameter Is Nothing Then Return Nothing


       Dim type = DirectCast(parameter, Type) ‘throw if not type and return nothing

       If Not type.IsEnum Then Return Nothing ‘if is not enum don’t continue to next line

       value = CInt(value) ‘make sure the value is anyhow compatible with integer.


       Return Nothing

    End Try

    BTW, FYI, I was wrong before, the converter returns image based on the enum type and the value.

  10. karl140.6 says:


    Try this out, it works in the designer and at runtime.

    You really never want to throw from the Convert method.

    Public Class DemoConverter

       Implements IValueConverter

       Public Enum Demo




       End Enum

       Public Function Convert(ByVal value As Object, ByVal targetType As System.Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.Convert

           If value Is Nothing OrElse parameter Is Nothing OrElse Not TypeOf value Is Integer Then Return Nothing

           If TypeOf parameter Is Type Then

               Dim type = DirectCast(parameter, Type)

               If Not type.IsEnum Then Return Nothing

               Dim enumValue As Demo

               If [Enum].TryParse(value.ToString(), enumValue) Then

                   ‘enumValue has a value you can use


                   ‘bummer, out of range value passed

               End If

           End If

       End Function

       Public Function ConvertBack(ByVal value As Object, ByVal targetType As System.Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.ConvertBack

       End Function

    End Class



  11. weitzhandler says:

    OK whatever.

    When using the CInt, the ToString is not necessary lol.

    Thanks a lot.

  12. weitzhandler says:

    And since I have a huge library of enum types, I prefer to make the validation at the beginning rather then TryParse of each enum, plus the ByRef is not what I am looking for.

    Anyway thanks for your suggestions.

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