Behaviors

• Nov 22, 2022
• 6 minutes to read

Behaviors can attach to visual controls and customize them (or extend their capabilities). Use this customization technique if you want your application to follow the MVVM pattern (no code-behind in Views). Our WPF product line ships with a wide variety of pre-defined Behaviors. You can find the list later in this topic. If no-built in Behavior meets your requirements, you can implement a custom class as described in the last section.

Run Demo: Behaviors Module in the WPF MVVM Demo

Add Behaviors to a Control

In XAML

The Interactivity.Interaction class implements the Behaviors attached property. To use a Behavior, place it in the following collection:

MainView.xaml

<TextBox Text="This control is focused on startup">
    <dxmvvm:Interaction.Behaviors>
        <dxmvvm:FocusBehavior/>
        <!--Other Behaviors-->
    </dxmvvm:Interaction.Behaviors>
</TextBox>

Behaviors may contain dependency properties:

MainView.xaml

<ListBox ...> 
    <dxmvvm:Interaction.Behaviors> 
        <dxmvvm:EventToCommand EventName="MouseDoubleClick" Command="{Binding EditCommand}"> 
            <dxmvvm:EventToCommand.EventArgsConverter> 
                <Common:ListBoxEventArgsConverter/> 
            </dxmvvm:EventToCommand.EventArgsConverter> 
        </dxmvvm:EventToCommand> 
    </dxmvvm:Interaction.Behaviors> 
    ...
</ListBox>

In Code-Behind

The following code sample attaches a BarSubItemThemeSelectorBehavior to a BarSubItem in code-behind. This example hides touch themes from the theme selector (sets the ShowTouchThemes property to false):

MainWindow.xaml

<Window ...
    xmlns:dxb="http://schemas.devexpress.com/winfx/2008/xaml/bars"
    xmlns:dxr="http://schemas.devexpress.com/winfx/2008/xaml/ribbon">
    <StackPanel>
        <dxr:RibbonControl>
            <dxr:RibbonDefaultPageCategory>
                <dxr:RibbonPage Caption="Home">
                    <dxr:RibbonPageGroup Caption="File">
                        <dxb:BarSubItem x:Name="barsubitem1"/>
                    </dxr:RibbonPageGroup>
                </dxr:RibbonPage>
            </dxr:RibbonDefaultPageCategory>
        </dxr:RibbonControl>
    </StackPanel>
</Window>

MainWindow.xaml.cs

using DevExpress.Mvvm.UI.Interactivity;
using DevExpress.Xpf.Bars;

// ...

    public MainWindow() {
        InitializeComponent();
        Interaction.GetBehaviors(barsubitem1).Add(new BarSubItemThemeSelectorBehavior {ShowTouchThemes=false });
    }

MainWindow.xaml.vb

Imports DevExpress.Mvvm.UI.Interactivity
Imports DevExpress.Xpf.Bars

Public Sub New()
    InitializeComponent()
    Interaction.GetBehaviors(barsubitem1).Add(New BarSubItemThemeSelectorBehavior With {
        .ShowTouchThemes = False
    })
End Sub

Add Behaviors to Controls of the Specified Type

Add a Single Behavior

You can attach a behavior to all objects of a specific type (and descendants) on a Window or a UserControl. To do that, place your declaration in Style. The following code sample uses the BehaviorsTemplate attached property to add the KeyToCommand behavior to each element of the GridControl type:

XAML

<Style TargetType="dxg:GridControl">
    <Setter Property="dxmvvm:Interaction.BehaviorsTemplate">
        <Setter.Value>
            <DataTemplate>
                <ContentControl>
                    <dxmvvm:KeyToCommand KeyGesture="CTRL+U" Command="{Binding UpdateCommand}"/>
                </ContentControl>
            </DataTemplate>
        </Setter.Value>
    </Setter>
</Style>

Add Multiple Behaviors

Place multiple behaviors to the ItemsControl element. The following code sample adds KeyToCommand and EventToCommand behaviors to each element of the GridControl type and its descendants:

MainView.xaml

<Style TargetType="dxg:GridControl">
    <Setter Property="dxmvvm:Interaction.BehaviorsTemplate">
        <Setter.Value>
            <DataTemplate>
                <ItemsControl>
                    <dxmvvm:KeyToCommand KeyGesture="CTRL+U" Command="{Binding UpdateCommand}"/>
                    <dxmvvm:EventToCommand EventName="MouseDoubleClick" Command="{Binding EditCommand}"> 
                        <dxmvvm:EventToCommand.EventArgsConverter> 
                            <Common:ListBoxEventArgsConverter/> 
                        </dxmvvm:EventToCommand.EventArgsConverter> 
                    </dxmvvm:EventToCommand> 
                </ItemsControl>
            </DataTemplate>
        </Setter.Value>
    </Setter>
</Style>

Predefined Behaviors

DevExpress WPF Product Line includes the following predefined behaviors:

EventToCommand

Executes a command in response to a raised event.

KeyToCommand

Allows you to bind a KeyGesture to a command.

FocusBehavior

Focuses a UI control without code-behind.

ValidationErrorsHostBehavior

Tracks validation errors within a UI container.

ConfirmationBehavior

Shows a confirmation message box before an application executes the specified command. Users can confirm or cancel the operation.

DependencyPropertyBehavior

Allows you to bind a ViewModel property to a control’s non-dependency property.

EnumItemsSourceBehavior

Binds a control’s ItemsSource property to an enumeration.

CompositeCommandBehavior

Allows you to aggregate multiple commands and execute them in a specific order.

FunctionBindingBehavior

Binds a ViewModel function’s result to a control’s property.

MethodToCommandBehavior

Binds a method of a ViewModel or control to a Command property of a control on a View.

ReadOnlyDependencyPropertyBindingBehavior

Allows you to bind read-only dependency and attached properties to a ViewModel’s properties.

CurrentWindowSerializationBehavior

Allows you to serialize/deserialize settings (size and state) of the associated view (or window).

BarSubItemThemeSelectorBehavior

Populates the associated BarSubItem with available themes and allows you to choose the application’s theme.

BarSplitItemThemeSelectorBehavior

Populates the associated BarSplitButtonItem with available themes and allows you to choose the application’s theme.

RibbonGalleryItemThemeSelectorBehavior

Populates the associated RibbonGalleryBarItem with available themes and allows you to choose the application’s theme.

GalleryThemeSelectorBehavior

Populates the associated GalleryControl with available themes and allows you to choose the application’s theme.

HamburgerSubMenuThemeSelectorBehavior

Populates the associated HamburgerSubMenu with available themes and allows you to choose the application’s theme.

RibbonGalleryItemThemePaletteSelectorBehavior

Populates the associated RibbonGalleryBarItem with the available palettes and allows you to choose the application theme’s palette.

Create a Custom Behavior

Each Behavior is a Behavior<T> class descendant. The T parameter defines the associated control type. The following code sample specifies a Behavior that you can apply only to a TextBox control or its descendants:

C#

public class ValidationBehavior : Behavior<TextBox> // TextBox is the AssociatedObject type 
{
    protected override void OnAttached() {
        base.OnAttached();
        // subscribe to the AssociatedObject events
    }
    protected override void OnDetaching() {
        // unsubscribe from the AssociatedObject events
        base.OnDetaching();
    }
}

VB.NET

Class SurroundingClass
    Public Class ValidationBehavior
    ' TextBox is the AssociatedObject type 
        Inherits Behavior(Of TextBox)
    End Class

    Protected Overrides Sub OnAttached()
    ' subscribe to the AssociatedObject events
        MyBase.OnAttached()
    End Sub

    Protected Overrides Sub OnDetaching()
    'unsubscribe from the AssociatedObject events
        MyBase.OnDetaching()
    End Sub
End Class

The Behavior<T> class contains the AssociatedObject property. DevExpress MVVM Framework specifies this property when you add a Behavior to the Behaviors collection.

After the AssociatedObject is specified, DevExpress MVVM Framework invokes the virtual OnAttached method. You can override this method to subscribe to AssociatedObject’s events and initialize its properties.

To unsubscribe from events, you can use the virtual OnDetaching method. DevExpress MVVM Framework invokes when the Behavior is destroyed.

C#

public class ValidationBehavior : Behavior<TextBox> {
    public static readonly DependencyProperty ValidForegroundProperty =
        DependencyProperty.Register("ValidForeground", typeof(Brush), typeof(ValidationBehavior),
        new PropertyMetadata(new SolidColorBrush(Colors.Black), (d, e) => ((ValidationBehavior)d).Update()));
    public static readonly DependencyProperty InvalidForegroundProperty =
        DependencyProperty.Register("InvalidForeground", typeof(Brush), typeof(ValidationBehavior), 
        new PropertyMetadata(new SolidColorBrush(Colors.Red), (d,e) => ((ValidationBehavior)d).Update()));
    public static readonly DependencyProperty InvalidValueProperty =
        DependencyProperty.Register("InvalidValue", typeof(string), typeof(ValidationBehavior),
        new PropertyMetadata(string.Empty, (d, e) => ((ValidationBehavior)d).Update()));
    public Brush ValidForeground {
        get { return (Brush)GetValue(ValidForegroundProperty); }
        set { SetValue(ValidForegroundProperty, value); }
    }
    public Brush InvalidForeground {
        get { return (Brush)GetValue(InvalidForegroundProperty); }
        set { SetValue(InvalidForegroundProperty, value); }
    }
    public string InvalidValue {
        get { return (string)GetValue(InvalidValueProperty); }
        set { SetValue(InvalidValueProperty, value); }
    }

    protected override void OnAttached() {
        base.OnAttached();
        AssociatedObject.TextChanged += OnAssociatedObjectTextChanged;
        Update();
    }
    protected override void OnDetaching() {
        AssociatedObject.TextChanged -= OnAssociatedObjectTextChanged;
        base.OnDetaching();
    }
    void OnAssociatedObjectTextChanged(object sender, TextChangedEventArgs e) {
        Update();
    }
    void Update() {
        if(AssociatedObject == null) return;
        if(AssociatedObject.Text == InvalidValue)
            AssociatedObject.Foreground = InvalidForeground;
        else AssociatedObject.Foreground = ValidForeground;
    }
}

VB.NET

Public Class ValidationBehavior
    Inherits Behavior(Of TextBox)

    Public Shared ReadOnly ValidForegroundProperty As DependencyProperty = DependencyProperty.Register("ValidForeground", GetType(Brush), GetType(ValidationBehavior), New PropertyMetadata(New SolidColorBrush(Colors.Black), Sub(d, e) CType(d, ValidationBehavior).Update()))
    Public Shared ReadOnly InvalidForegroundProperty As DependencyProperty = DependencyProperty.Register("InvalidForeground", GetType(Brush), GetType(ValidationBehavior), New PropertyMetadata(New SolidColorBrush(Colors.Red), Sub(d,e) CType(d, ValidationBehavior).Update()))
    Public Shared ReadOnly InvalidValueProperty As DependencyProperty = DependencyProperty.Register("InvalidValue", GetType(String), GetType(ValidationBehavior), New PropertyMetadata(String.Empty, Sub(d, e) CType(d, ValidationBehavior).Update()))
    Public Property ValidForeground() As Brush
        Get
            Return CType(GetValue(ValidForegroundProperty), Brush)
        End Get
        Set(ByVal value As Brush)
            SetValue(ValidForegroundProperty, value)
        End Set
    End Property
    Public Property InvalidForeground() As Brush
        Get
            Return CType(GetValue(InvalidForegroundProperty), Brush)
        End Get
        Set(ByVal value As Brush)
            SetValue(InvalidForegroundProperty, value)
        End Set
    End Property
    Public Property InvalidValue() As String
        Get
            Return CStr(GetValue(InvalidValueProperty))
        End Get
        Set(ByVal value As String)
            SetValue(InvalidValueProperty, value)
        End Set
    End Property

    Protected Overrides Sub OnAttached()
        MyBase.OnAttached()
        AddHandler AssociatedObject.TextChanged, AddressOf OnAssociatedObjectTextChanged
        Update()
    End Sub
    Protected Overrides Sub OnDetaching()
        RemoveHandler AssociatedObject.TextChanged, AddressOf OnAssociatedObjectTextChanged
        MyBase.OnDetaching()
    End Sub
    Private Sub OnAssociatedObjectTextChanged(ByVal sender As Object, ByVal e As TextChangedEventArgs)
        Update()
    End Sub
    Private Sub Update()
        If AssociatedObject Is Nothing Then
            Return
        End If
        If AssociatedObject.Text = InvalidValue Then
            AssociatedObject.Foreground = InvalidForeground
        Else
            AssociatedObject.Foreground = ValidForeground
        End If
    End Sub
End Class

MainView.xaml

<TextBox Text="Text">
    <dxmvvm:Interaction.Behaviors>
        <Behaviors:ValidationBehavior ValidForeground="{Binding ValidBrush}"
                                      InvalidForeground="{Binding InvalidBrush}"
                                      InvalidValue="{Binding InvalidValue}"/>
    </dxmvvm:Interaction.Behaviors>
</TextBox>

View Example: WPF MVVM Behaviors - Create a Custom Attached Behavior