Calling an object method in a data trigger

Calling a method on an instance of an object in WPF is not as easy to figure out, but with the help of this Internet thing I managed it.

Say you have a DataTemplate that renders a WorkItemType as a button that is selectable:

1   1: <DataTemplate DataType="{x:Type tfswitc:WorkItemType}">

1   2:     <DockPanel>

1   3:         <Image DockPanel.Dock="Left"

1   4:                x:Name="wiImage"

1   5:                Width="16"

1   6:                Height="16"

1   7:                Source="pack://application:,,/Resources/Images/WorkItems/unknown.gif">

1   8:         </Image>

1   9:         <Button x:Name="wiButton"

1  10:                 Content="{Binding Name}"

1  11:                 Style="{DynamicResource WelcomeButtonStyle}"

1  12:                 CommandParameter="{Binding}"

1  13:                 Command="Controlers:TeamSystemCommands.ChangeWorkItemTypeCommand">

1  14:         </Button>

1  15:     </DockPanel>

1  16: </DataTemplate>

Now, if I wanted to call a method on an instance of that WorkItemType and perform some action, then I would need a DataTrigger:

1   1: <DataTemplate DataType="{x:Type tfswitc:WorkItemType}">

1   2:     <DockPanel>

1   3:         <Image DockPanel.Dock="Left"

1   4:                x:Name="wiImage"

1   5:                Width="16"

1   6:                Height="16"

1   7:                Source="pack://application:,,/Resources/Images/WorkItems/unknown.gif">

1   8:         </Image>

1   9:         <Button x:Name="wiButton"

1  10:                 Content="{Binding Name}"

1  11:                 Style="{DynamicResource WelcomeButtonStyle}"

1  12:                 CommandParameter="{Binding}"

1  13:                 Command="Controlers:TeamSystemCommands.ChangeWorkItemTypeCommand">

1  14:         </Button>

1  15:     </DockPanel>

1  16:     <DataTemplate.Triggers>

1  17:         <DataTrigger Value="False">

1  18:             <DataTrigger.Binding>

1  19:                 <Binding>

1  20:                     <Binding.Source>

1  21:                         <ObjectDataProvider ObjectType="{x:Type tfswitc:WorkItemType}"

1  22:                                             MethodName="SupportedByHeat" />

1  23:                     </Binding.Source>

1  24:                 </Binding>

1  25:             </DataTrigger.Binding>

1  26:             <Setter TargetName="wiButton"

1  27:                     Property="IsEnabled"

1  28:                     Value="False" />

1  29:             <Setter TargetName="wiButton"

1  30:                     Property="ToolTip"

1  31:                     Value="You will need to add the 'HeatITSM.Ref' field to use this work item." />

1  32:         </DataTrigger>

1  33:     </DataTemplate.Triggers>

1  34: </DataTemplate>

This will Call the method and if it returns false, it will disable the button and set a tooltip.

Now, this should work, but my SupportedByHeat method is an Extension method defined as:

1   1: Imports Microsoft.TeamFoundation.WorkItemTracking.Client

1   2:

1   3: Namespace TeamFoundationExtensions

1   4:

1   5:

1   6:     Module WorkItemTypeExtensions

1   7:

1   8:         <System.Runtime.CompilerServices.Extension()> _

1   9:       Public Function SupportedByHeat(ByVal wit As WorkItemType) As Boolean

1  10:             Dim c As Controlers.TeamSystemControler(Of MainWindow)

1  11:             c = Application.ControlerFactory.GetControler(Of Controlers.TeamSystemControler(Of MainWindow))()

1  12:             Return c.CheckWorkItemField(wit)

1  13:         End Function

1  14:

1  15:     End Module

1  16:

1  17: End Namespace

And this does not seam to work even if I import the namespace in the XAML:

1   1: <UserControl x:Class="SelectWorkItemType"

1   2:   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

1   3:   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

1   4:   xmlns:d="http://schemas.microsoft.com/expression/blend/2006"

1   5:   xmlns:tfs="clr-namespace:Microsoft.TeamFoundation.Client;assembly=Microsoft.TeamFoundation.Client"

1   6:   xmlns:tfswitc="clr-namespace:Microsoft.TeamFoundation.WorkItemTracking.Client;assembly=Microsoft.TeamFoundation.WorkItemTracking.Client"

1   7:   xmlns:tfse="clr-namespace:Hinshelwood.TFSHeatITSM.TeamFoundationExtensions"

1   8:   xmlns:local="clr-namespace:Hinshelwood.TFSHeatITSM"

1   9:   xmlns:Controlers="clr-namespace:Hinshelwood.TFSHeatITSM.Controlers"

1  10:   xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

1  11:   mc:Ignorable="d">

The error message that is received is:

System.Windows.Data Error: 34 : ObjectDataProvider: Failure trying to invoke method on type; Method=‘SupportedByHeat’; Type=‘WorkItemType’; Error=‘No method was found with matching parameter signature.’ MissingMethodException:‘System.MissingMethodException: Method ‘Microsoft.TeamFoundation.WorkItemTracking.Client.WorkItemType.SupportedByHeat’ not found.
at System.RuntimeType.InvokeMember(String name, BindingFlags bindingFlags, Binder binder, Object target, Object[] providedArgs, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParams)
_at System.Type.InvokeMember(String name, BindingFlags invokeAttr, Binder binder, Object target, Object[] args, CultureInfo culture)
at System.Windows.Data.ObjectDataProvider.InvokeMethodOnInstance(Exception& e)’_

As you can see, during the binding the extension method is not evaluated.

During my investigation I came across WPFix Part 3 (Extension Methods) that intoned that there is indeed some solution, but it is complicated requiring the use of Lambda expressions.

I am looking for an easy solution :)

Technorati Tags: .NET WPF WIT TFS

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