Custom control derived from RadCombobox errors in Expression Blend

[DOUG]

I have created a custom control derived from RadCombobox. It compiles and runs fine in Visual Studio. But if I use Expression Blend to view a screen containing my custon control, I receive a design time error stating "Object reference not set to an instance of an object". This happens even if the derived class contains an insignificant amount of code. If I place RadCombobox directly on the screen (e.g. without wrapping it in a custom control), it shows up fine.

Here is my custom control:

    public class ccComboBox : RadComboBox
    {
        public int i;
    }

Here is my xaml:
    <Grid>
        <StackPanel>
            <telerik:RadComboBox Height="30" Width="200" Background="LightBlue"/>
            <cc:ccComboBox Height="30" Width="200" Background="LightBlue"/>
            <cc:ccDatePicker />
        </StackPanel>
    </Grid>

Only the ccComboBox xaml causes the error. ccDatePicker is derived from RadDatePicker and works fine.

Any help is greatly appreciated.

Doug

[Valeri Hristov]

Hi DOUG,

What version of RadControls for WPF are you using? What's the .NET version of your application (3.5 or 4)?

I created a very simple application that seems to work fine in both Visual Studio 2010 and Blend 4, please, find it attached. Let me know if I am missing something.

All the best,
Valeri Hristov
the Telerik team

[DOUG]

Valeri,

I am using: .Net 4.0, Blend version 4.0.20525.0, Telerik WPF VSExtensions 2011.01.315.0, Visual Studio 2010 Professional 10.0.409219.1 SP1REL. The screen shows up fine in Visual Studio, but it causes the following error for the derived control when shown in the Blend designer: "Object reference not set to an instance of an object".

Thanks,

Doug

[Valeri Hristov]

Hi Doug,

What's the version of the Telerik assemblies you are using? Can you prepare and send us a simple application (or update mine) that can be used to observe the problem?

Best wishes,
Valeri Hristov
the Telerik team