Error: Cannot create an instance of xxx

[ShaningYu]

In one of the xaml file, received such an error at the line of code:

            <userControls:GraphComparison x:Name="GraphComp"/>

Error 114 Cannot create an instance of "GraphComparison". C:\...\Views\CompareCycles.xaml 270 13

The detail shows that
Cannot find a Resource with the Name/Key CommonBorder [Line: 10 Position: 44]
   at System.Windows.Application.LoadComponent(Object component, Uri resourceLocator)
   at xxx.UserControls.GraphComparison.InitializeComponent() in C:\...\obj\Debug\UserControls\GraphComparison.g.i.cs:line 60
   at xxx.UserControls.GraphComparison..ctor() in C:\...\UserControls\GraphComparison.xaml.cs:line 20

However, I did declare:
xmlns:userControls="clr-namespace:npsNavSL.UserControls"
and found nothing wrong.  Wish can get someone's hint for this bug.  Thanks.

[DominiqueBroux]

It's likely an error in the XAML part of your GraphComparison user control.

[ShaningYu]

The GraphComparison.xmal displays well.  In the xaml page that loads the GraphComparison.xaml shows the error message in the 1st post of this thread.  How to debug it?  Thanks.

[JenniferNery]

You can check that when you type "<userControls:" in XAML, GraphicSource is shown in the intellisense. If it can't find it then maybe the XAML namespace declaration could be wrong. Another way to check is to put a break point on GraphicSource class, to see if it comes through there. Check the class namespace is the same as what you define for xmlns:userControls="...".

[ShaningYu]

I  typed "<userControls:" in XAML, GraphicSource is shown in the intellisense (see the image attached).  What other approaches can be used for the debug?  Thanks.

[JenniferNery · Accepted solution]

Please check...

If it can't find it then maybe the   XAML namespace declaration could be wrong. Another way to check is to put a break point on GraphicSource class, to see if it comes through there. Check the class namespace is the same as what you define for xmlns:userControls="...".