Implement Multiselect in WPF DataGrid in proper WPF way with Multiselect Behavior and without any code behind

Introduction

In this article you will see how to implement multiselect in WPF DataGrid in proper way when you are following MVVM pattern. In this article you will see how to implement a behavior to your DataGrid so that we can achieve multiselect.

Behaviors are introduced with Expression Blend, to encapsulate pieces of functionality into a reusable component. These components can then be attached to controls to give them an additional behavior.

Background

Multiselect is something which is like a must have feature in any control which displays multiple items, but unfortunately it is not straight forward in WPF when you are an MVVM developer. We need to attach a multiselect behavior to controls like DataGrid in order to get multiselect working.

Problem it addresses

In DataGrid, the property “SelectedItems” does not have an accessible setter. So we need alternate ways to get the list of selected items.

Requirements

Here you need to add reference to System.Windows.Interactivity. If you have installed blend, then it is available in C:\Program Files (x86)\Microsoft SDKs\Expression\Blend 3\Interactivity\Libraries\WPF.

Using the code

  1. Add reference to System.Windows.Interactivity
  2. Add DataGrid to your xaml.
<window []="" xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity">
    <grid>
        <datagrid itemssource="{Binding Values}">
        </datagrid>
    </grid>
</window>
  1. create view model with a public property called SelectedItems.
namespace WpfApplicationTest
{
    using System.Collections;
    using System.Collections.Specialized;

    internal class MainWindowViewModel
    {
        public IList Values { get; set; }

        public MainWindowViewModel()
        {
            this.Values = new StringCollection { "test1", "test2", "test3", "test4", "test5" };
        }

        public IList SelectedItems { get; set; }
    }
}
  1. Create multiselect behavior as shown below.
namespace WpfApplicationTest
{
    using System;
    using System.Windows.Controls;
    using System.Windows.Interactivity;

    public class MultiSelectBehavior : Behavior<datagrid>
    {
        protected override void OnAttached()
        {
            base.OnAttached();

            ((MainWindowViewModel)this.AssociatedObject.DataContext).SelectedItems = this.AssociatedObject.SelectedItems;
        }
    }
}
  1. Now add this behavior to DataGrid. Also don’t forget to make SelectionMode=”Extended”. This will help you to select row by pressing Ctrl key.
<window []="">
    <grid>
        <datagrid itemssource="{Binding Values}" SelectionMode="Extended">
            <i:interaction.behaviors>
                <wpfapplicationtest:multiselectbehavior></wpfapplicationtest:multiselectbehavior>
            </i:interaction.behaviors>
        </datagrid>
    </grid>
</window>

Point of interest

If you have multiple DataGrid, then you need multiple Multiselect behaviors, one way to avoid this is by creating switch in MultiselectBehavior.

namespace WpfApplicationTest
{
    using System;
    using System.Windows.Controls;
    using System.Windows.Interactivity;

    public class MultiSelectBehavior : Behavior<datagrid>
    {
        protected override void OnAttached()
        {
            base.OnAttached();
            switch (this.AssociatedObject.Name)
            {
                case "DataGrid1":
                    ((MainWindowViewModel)this.AssociatedObject.DataContext).SelectedItemsForDataGrid1 = this.AssociatedObject.SelectedItems;

                    break;

                case "DataGrid2":
                    ((MainWindowViewModel)this.AssociatedObject.DataContext).SelectedItemsForDataGrid1 = this.AssociatedObject.SelectedItems;

                    break;

                default:
                    break;
            }
        }
    }
}

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Libish Varghese Jacob

Libish Varghese JacobI am currently working as a lead engineer in one of the leading wind turbine manufacturing firm. I have wide range of interests and getting my hands dirty in technology is one among them. I use this platform primarily as my knowledge base. I also use this platform to share my experience and experiments so that it might help someone who is walking the way I already did. The suggestions expressed here are the best to my knowledge at the time of writing and this may not necessarily be the best possible solution. I would pretty much appreciate if you could comment on it to bring into my notice on what could have been done better.