EventToCommand Class
Executes a command in response to a raised event.
Namespace: DevExpress.Mvvm.UI
Assembly: DevExpress.Xpf.Core.v23.2.dll
NuGet Package: DevExpress.Wpf.Core
Declaration
Remarks
EventToCommand: Basic Setup Example
Review the following example for information about the EventToCommand:
Specify a Source Object
A source object is an object that raises events. The default source object is a control associated with the EventToCommand behavior.
<UserControl>
<dxmvvm:Interaction.Behaviors>
<dxmvvm:EventToCommand EventName="Loaded" Command="{Binding InitializeCommand}"/>
</dxmvvm:Interaction.Behaviors>
</UserControl>
You can specify a different source object for the EventToCommand:
- SourceObject
- Allows you to bind the behavior’s source object to a control.
- SourceName
- Specifies the name of the behavior’s source object.
<UserControl>
<dxmvvm:Interaction.Behaviors>
<dxmvvm:EventToCommand SourceName="list" EventName="MouseDoubleClick" Command="{Binding InitializeCommand}"/>
<dxmvvm:EventToCommand SourceObject="{Binding ElementName=list}"
EventName="MouseDoubleClick"
Command="{Binding InitializeCommand}"/>
</dxmvvm:Interaction.Behaviors>
<ListBox x:Name="list"/>
</UserControl>
Specify an Event
You can use one of the following properties to specify an event:
- EventName
If the source object contains the event, use this property to specify the event’s name.
<dxe:TextEdit> <dxmvvm:Interaction.Behaviors> <dxmvvm:EventToCommand Command="{Binding LoadedCommand}" EventName ="Loaded"/> </dxmvvm:Interaction.Behaviors> </dxe:TextEdit>- Event
This property is of the RoutedEvent type. Use it to specify a routed event.
<dxe:TextEdit> <dxmvvm:Interaction.Behaviors> <dxmvvm:EventToCommand Command="{Binding LoadedCommand}" Event="FrameworkElement.Loaded"/> <dxmvvm:EventToCommand Command="{Binding TextChangedCommand}" Event="TextBoxBase.TextChanged"/> </dxmvvm:Interaction.Behaviors> </dxe:TextEdit>
Pass a Parameter to the Bound Command
Use the CommandParameter property to pass a parameter to a command:
<ListBox x:Name="list">
<dxmvvm:Interaction.Behaviors>
<dxmvvm:EventToCommand EventName="MouseDoubleClick"
Command="{Binding EditCommand}"
CommandParameter="{Binding ElementName=list, Path=SelectedItem}"/>
</dxmvvm:Interaction.Behaviors>
</ListBox>
Use one of the following properties to pass an event’s arguments to a command:
- PassEventArgsToCommand
Specifies if the event’s arguments are passed to the command.
<ListBox x:Name="list"> <dxmvvm:Interaction.Behaviors> <dxmvvm:EventToCommand EventName="MouseDoubleClick" Command="{Binding EditCommand}" PassEventArgsToCommand="True"/> </dxmvvm:Interaction.Behaviors> </ListBox>- EventArgsConverter
Allows you to maintain a clean MVVM pattern and convert the event’s arguments to an object suitable for the command.
<ListBox x:Name="list"> <dxmvvm:Interaction.Behaviors> <dxmvvm:EventToCommand EventName="MouseDoubleClick" Command="{Binding EditCommand}" EventArgsConverter="{dxmvvm:ItemsControlMouseEventArgsConverter}"/> </dxmvvm:Interaction.Behaviors> </ListBox>
Pass a Parameter Back to the Bound Event
A parameter that a command processes may indicate to the source object how to implement a certain action. You can pass the parameter from the command to the bound event, so that the source object can determine how to proceed. Create a converter class that implements IEventArgsTwoWayConverter and assign the class object to the EventArgsConverter property.
The code sample below uses the back conversion to validate data:
<dxe:TextEdit EditValue="{Binding UserName}">
<dxmvvm:Interaction.Behaviors>
<dxmvvm:EventToCommand Command="{Binding UserNameValidationCommand}"
EventArgsConverter="{local:ValidateEventArgsConverter}"
EventName="Validate"/>
</dxmvvm:Interaction.Behaviors>
</dxe:TextEdit>
public class ValidationArgs {
public string ErrorContent { get; private set; }
public object Value { get; }
public ValidationArgs(object value) => Value = value;
public void SetError(bool isValid, string errorContent) => ErrorContent = isValid ? null : errorContent;
}
public class ValidateEventArgsConverter : EventArgsConverterBase<ValidationEventArgs> {
protected override object Convert(object sender, ValidationEventArgs e) => new ValidationArgs(e.Value);
protected override void ConvertBack(object sender, ValidationEventArgs e, object parameter) {
var args = parameter as ValidationArgs;
e.IsValid = args.ErrorContent == null;
e.ErrorContent = args.ErrorContent;
}
}
Specify Modifier Keys as an Additional Condition of the Command Execution
Use the ModifierKeys property to specify keys a user should press to invoke the command.
In the code sample below, the bound EditCommand is invoked when a user clicks a ListBoxItem and presses the Ctrl and Alt keys.
<ListBox ItemsSource="{Binding Persons}">
<dxmvvm:Interaction.Behaviors>
<dxmvvm:EventToCommand EventName="MouseLeftButtonUp"
Command="{Binding EditCommand}"
EventArgsConverter="{dxmvvm:ItemsControlMouseEventArgsConverter}"
ModifierKeys="Ctrl+Alt"/>
</dxmvvm:Interaction.Behaviors>
</ListBox>
Related API
| Property | Description |
|---|---|
| MarkRoutedEventsAsHandled | Gets or sets whether the associated routed event is marked as handled when the command is executed. This is a dependency property. |
| DispatcherPriority | Gets or sets the priority of the Dispatcher that invokes the associated command. This is a dependency property. |
| AllowChangingEventOwnerIsEnabled | Gets or sets whether the event source object’s IsEnabled property value reflects the command’s CanExecute method value. This is a dependency property. |
| ProcessEventsFromDisabledEventOwner | Gets or sets whether the EventToCommand processes events for the source object even if the source object is disabled. This is a dependency property. |
Related GitHub Examples
The following code snippets (auto-collected from DevExpress Examples) contain references to the EventToCommand class.
Note
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