CompositeCommandBehavior

• Jun 07, 2019
• 3 minutes to read

The grouping and execution of multiple commands in a sequence are common tasks when creating a WPF MVVM application. However, standard WPF mechanisms do not provide a convenient way to perform these actions.

The CompositeCommandBehavior can be used to aggregate and execute multiple commands

XAML

<dxb:BarButtonItem ... >
    <dxmvvm:Interaction.Behaviors>
        <dxmvvm:CompositeCommandBehavior>
            <dxmvvm:CommandItem Command="{Binding SaveCommand}"/>
            <dxmvvm:CommandItem Command="{Binding CloseCommand}"/>
        </dxmvvm:CompositeCommandBehavior>
    </dxmvvm:Interaction.Behaviors> 
</dxb:BarButtonItem>

To use the CompositeCommandBehavior, it is necessary to specify its child CommandItem items bound to the required ViewModel’s command.

The CompositeCommand property returns the resulting aggregate function.

The CompositeCommand can only be executed when all of its inner commands can be executed (the CommandItem.CanExecute property is set to true). This is the default behaviour.

Set the CompositeCommandBehavior.CanExecuteCondition property to AnyCommandCanBeExecuted to allow running the CompositeCommand when at least one of its inner commands can be executed (the CommandItem.CanExecute property is set to true).

Example

View Example

MainView.xaml

<UserControl 
    x:Class="CompositeCommandBehaviorExample.View.MainView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core" 
    xmlns:dxb="http://schemas.devexpress.com/winfx/2008/xaml/bars"
    xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm" 
    xmlns:vm="clr-namespace:CompositeCommandBehaviorExample.ViewModel" 
    mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="300"
    DataContext="{dxmvvm:ViewModelSource Type=vm:MainViewModel}">
    <dxmvvm:Interaction.Behaviors>
        <dx:DXMessageBoxService />
    </dxmvvm:Interaction.Behaviors>
    <Grid>
        <dxb:BarManager>
            <dxb:BarManager.Bars>
                <dxb:Bar Caption="Main Menu" IsMainMenu="True">
                    <dxb:BarButtonItem Content="Save" Command="{Binding SaveCommand}"/>
                    <dxb:BarButtonItem Content="Close" Command="{Binding CloseCommand}"/>
                    <dxb:BarButtonItem Content="Save and Close">
                        <dxmvvm:Interaction.Behaviors>
                            <dxmvvm:CompositeCommandBehavior>
                                <dxmvvm:CommandItem Command="{Binding SaveCommand}"/>
                                <dxmvvm:CommandItem Command="{Binding CloseCommand}"/>
                            </dxmvvm:CompositeCommandBehavior>
                        </dxmvvm:Interaction.Behaviors> 
                    </dxb:BarButtonItem>
                </dxb:Bar>
            </dxb:BarManager.Bars>
            <Grid>
                <TextBox Text="{Binding Text,Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" AcceptsReturn="True"/>
            </Grid>
        </dxb:BarManager>
    </Grid>
</UserControl>

MainViewModel.cs

using System;
using System.Linq;
using DevExpress.Mvvm;
using DevExpress.Mvvm.POCO;
using System.Collections.Generic;

namespace CompositeCommandBehaviorExample.ViewModel {
    public class MainViewModel : ViewModelBase {
        protected MainViewModel() { }
        public static MainViewModel Create() {
            return ViewModelSource.Create(() => new MainViewModel());
        }

        public virtual string Text { get; set; }
        public virtual string SavedText { get; set; }
        bool IsSaved { get { return SavedText == Text; } }
        protected IMessageBoxService MessageService { get { return GetService<IMessageBoxService>(); } }

        public void Save() {
            SavedText = Text;
        }
        public bool CanSave() {
            return !IsSaved;
        }
        public void Close() {
            if(!IsSaved && MessageService.ShowMessage("Are you sure to close unsaved document", "Warning", MessageButton.YesNo) == MessageResult.No)
                return;
            Text = String.Empty;
            SavedText = String.Empty;
        }
        public bool CanClose() {
            return !String.IsNullOrEmpty(Text);
        }
    }
}

MainViewModel.vb

Imports System
Imports System.Linq
Imports DevExpress.Mvvm
Imports DevExpress.Mvvm.POCO
Imports System.Collections.Generic

Namespace CompositeCommandBehaviorExample.ViewModel
    Public Class MainViewModel
        Inherits ViewModelBase

        Protected Sub New()
        End Sub
        Public Shared Function Create() As MainViewModel
            Return ViewModelSource.Create(Function() New MainViewModel())
        End Function

        Public Overridable Property Text() As String
        Public Overridable Property SavedText() As String
        Private ReadOnly Property IsSaved() As Boolean
            Get
                Return SavedText = Text
            End Get
        End Property
        Protected ReadOnly Property MessageService() As IMessageBoxService
            Get
                Return GetService(Of IMessageBoxService)()
            End Get
        End Property

        Public Sub Save()
            SavedText = Text
        End Sub
        Public Function CanSave() As Boolean
            Return Not IsSaved
        End Function
        Public Sub Close()
            If (Not IsSaved) AndAlso MessageService.ShowMessage("Are you sure to close unsaved document", "Warning", MessageButton.YesNo) = MessageResult.No Then
                Return
            End If
            Text = String.Empty
            SavedText = String.Empty
        End Sub
        Public Function CanClose() As Boolean
            Return Not String.IsNullOrEmpty(Text)
        End Function
    End Class
End Namespace