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c#wpfxamlprism

Upgrading XAML Behaviors

I've updated PRISM and now my XAML files are returning errors. I have done some research on how to fix it and it seems that changing the xmlns:i tag would do the job.

This is how it was:

xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"

and I changed it to:

xmlns:i="http://schemas.microsoft.com/xaml/behaviors"

The issue is now that i'm getting an error on the Class tag:

<Window x:Class="X.StatusHostWindow">

The error that I get is:

The specified value cannot be assigned to the collection. The following type was expected: "Behavior".

My code behind class has the class Window inherited, so if I want to inherit the class Behavior it is complaining that I cannot have multiple inheritances.

Code behind error stating that the class cannot have multiple base classes.

Any idea on how to fix this?

XAML code:

<Window x:Class="X.StatusHostWindow"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:po="http://schemas.microsoft.com/winfx/2006/xaml/presentation/options"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:TemplateSelectors="clr-namespace:X.TemplateSelectors"
    xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
    xmlns:s="clr-namespace:System;assembly=mscorlib"
    xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
    xmlns:local="clr-namespace:X.Client.Controls"
    xmlns:Shared="clr-namespace:X.Common.Shared;assembly=X"
    xmlns:converters="clr-namespace:X.Client.Controls.Convertors"
    xmlns:Behaviors="clr-namespace:X.Client.Controls.Behaviors" ShowActivated="False" 
    AllowsTransparency="True"
    WindowStyle="None"
    ShowInTaskbar="False"
    Background="Transparent" 
    Topmost="True" 
    UseLayoutRounding="True"
    DataContext="{Binding RelativeSource={RelativeSource Self}}"
    >
<Window x:Class="X.Client.Controls.StatusHostWindow"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:po="http://schemas.microsoft.com/winfx/2006/xaml/presentation/options"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:TemplateSelectors="clr-namespace:X.Client.Controls.TemplateSelectors"
    xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
    xmlns:s="clr-namespace:System;assembly=mscorlib"
    xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
    xmlns:local="clr-namespace:X.Client.Controls"
    xmlns:Shared="clr-namespace:X.Common.Shared;assembly=X.Common.Infrastructure"
    xmlns:converters="clr-namespace:X.Client.Controls.Convertors"
    xmlns:Behaviors="clr-namespace:X.Client.Controls.Behaviors" ShowActivated="False" 
    AllowsTransparency="True"
    WindowStyle="None"
    ShowInTaskbar="False"
    Background="Transparent" 
    Topmost="True" 
    UseLayoutRounding="True"
    DataContext="{Binding RelativeSource={RelativeSource Self}}"
    >
<Window.Resources>
    <converters:SeverityToBrushConverter x:Key="severityToBrushConverter"/>

    <local:TriggersCollection x:Key="removeTriggers" x:Shared="false">
        <i:EventTrigger EventName="MouseLeftButtonDown">
            <i:InvokeCommandAction Command="{Binding RemoveStatusCommand, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}"
                                   CommandParameter="{Binding}"
                                   />
        </i:EventTrigger>
    </local:TriggersCollection>

I get an error on <i:EventTrigger> tag:

The name eventTrigger does not exist in the namespace http://schemas.microsoft.com/expression/2010/interactivity.

That is why I've updated it to:

xmlns:i="http://schemas.microsoft.com/xaml/behaviors
Solution

  • In your XAML you do not use the right namespace. Both of the following namespaces are from the legacy interactivity library that you want to replace.

    • xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
    • xmlns:ei=http://schemas.microsoft.com/expression/2010/interactions" (unused in your sample)

    Replace them with the new XAML behaviors namespace.

    xmlns:i="http://schemas.microsoft.com/xaml/behaviors"

    The error in your code-behind comes from the fact, that C# only supports single inheritance, You cannot derive from multiple classes like Window and Behavior.

    Class types support single inheritance and polymorphism, mechanisms whereby derived classes can extend and specialize base classes.

    This has nothing to do with behaviors or the upgrade, it was not possible before either. The intention of behaviors is to create reusable components that encapsulate a certain behavior that can be attached to UI elements. Usually, you attach a behavior in XAML using the i:Interaction.Behaviors element, e.g.:

    <TextBox>
    <i:Interaction.Behaviors>
        <local:MySpecialHighlightingBehavior/>
    </i:Interaction.Behaviors>
</TextBox>

    Consequently, deriving both from a UI element and a behavior does not make sense.