Using the “assembly” when mapping clr-namespace
I was playing around today with Data binding in WPF using the ObjectDataProvider. It is a powerful concept and you can apply it effectively if you understand it well. Beatriz Costa has been blogging for a while about DataBinding and her blog is a great resource.
Since the Feb CTP of WinFX the syntax has changed for mapping a CLR namespace to a XML namespace. Using the new syntax the mapping can be part of the root tag as:
<Grid
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/interactivedesigner/2006"
mc:Ignorable="d"
Background="#FFFFFFFF"
x:Name="DocumentRoot"
x:Class="UntitledProject1.Scene1"
Width="640"
Height="480"
xmlns:f="clr-namespace:MyHelper;assembly=MyHelper"
xmlns:system="clr-namespace:System;assembly=mscorlib">
Note the highlighted line which contains the mapping. With this concise syntax, we are creating a XML namespace “system” which maps to the CLR namespace of “System”. In the same line we also have an “assembly” attribute. This tells the XAML parser that the aforementioned namespace is not in the current assembly but lies in an external assembly (in this case “mscorlib”).
Thus when the XAML parser sees a fragment like below:
<ObjectDataProvider
x:Key="odp_1"
ObjectType="{x:Type f:MyHelper}"/>
<ObjectDataProvider
x:Key="odp_2"
MethodName="GetPhotos"
ObjectInstance="{StaticResource odp_1}">
<ObjectDataProvider.MethodParameters>
<system:String>pavan-podila</system:String>
</ObjectDataProvider.MethodParameters>
</ObjectDataProvider>
it would know that the “system:String” is a Type defined in the CLR “System” namespace which lies in the mscorlib assembly.
I have had enough trouble debugging a solution when I missed the “assembly” attribute. I would keep getting a XamlParseException and when I drill down into the InnerException it would say:
{"Error at element 'String' in markup file 'TestUI;component/scene1.xaml' : 'f:MyHelper' string cannot be converted to object of type 'System.Type'."}
After scratching my head for a while it dawned on me that I was missing the “assembly” attribute. The mapping should be:
xmlns:f="clr-namespace:MyHelper;assembly=MyHelper"
WITH the assembly attribute!
posted by Pavan Podila @ 6:11 PM
