WPF DataGrid full row selection

Based on previous comment from Aleksey L., here is the solution with DataGridBehavior class with FullRowSelect dependency property.

Behavior will automatically attach MouseDown event handler. Also, it will set "SelectionMode = DataGridSelectionMode.Single" so it will work properly with DataContext and SelectedItem binding.

XAML

<UserControl x:Class="WpfDemo.Views.Default"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:b="clr-namespace:WpfDemo.Behaviors"
         mc:Ignorable="d" 
         d:DesignHeight="300">

        <DataGrid b:DataGridBehavior.FullRowSelect="True">
              ...
        </DataGrid>             

DataGridBehavior class

using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace WpfDemo.Behaviors
{
    /// <summary>
    /// Extends <see cref="DataGrid"/> element functionality.
    /// </summary>
    public static class DataGridBehavior
    {
        #region - Dependency properties -

        /// <summary>
        /// Forces row selection on empty cell, full row select.
        /// </summary>
        public static readonly DependencyProperty FullRowSelectProperty = DependencyProperty.RegisterAttached("FullRowSelect",
            typeof(bool),
            typeof(DataGridBehavior),
            new UIPropertyMetadata(false, OnFullRowSelectChanged));

        #endregion

        #region - Public methods -

        /// <summary>
        /// Gets property value.
        /// </summary>
        /// <param name="grid">Frame.</param>
        /// <returns>True if row should be selected when clicked outside of the last cell, otherwise false.</returns>
        public static bool GetFullRowSelect(DataGrid grid)
        {
            return (bool)grid.GetValue(FullRowSelectProperty);
        }

        /// <summary>
        /// Sets property value.
        /// </summary>
        /// <param name="grid">Frame.</param>
        /// <param name="value">Value indicating whether row should be selected when clicked outside of the last cell.</param>
        public static void SetFullRowSelect(DataGrid grid, bool value)
        {
            grid.SetValue(FullRowSelectProperty, value);
        }

        #endregion

        #region - Private methods -

        /// <summary>
        /// Occurs when FullRowSelectProperty has changed.
        /// </summary>
        /// <param name="depObj">Dependency object.</param>
        /// <param name="e">Event arguments.</param>
        private static void OnFullRowSelectChanged(DependencyObject depObj, DependencyPropertyChangedEventArgs e)
        {
            DataGrid grid = depObj as DataGrid;
            if (grid == null)
                return;

            if (e.NewValue is bool == false)
            {
                grid.MouseDown -= OnMouseDown;

                return;
            }

            if ((bool)e.NewValue)
            {
                grid.SelectionMode = DataGridSelectionMode.Single;

                grid.MouseDown += OnMouseDown;
            }
        }

        private static void OnMouseDown(object sender, MouseButtonEventArgs e)
        {
            var dependencyObject = (DependencyObject)e.OriginalSource;

            while ((dependencyObject != null) && !(dependencyObject is DataGridRow))
            {
                dependencyObject = VisualTreeHelper.GetParent(dependencyObject);
            }

            var row = dependencyObject as DataGridRow;
            if (row == null)
            {
                return;
            }

            row.IsSelected = true;
        }

        #endregion
    }
}

There is one more solution if you can use code behind in your project. You can handle mouse down event of datagrid and programmatically select the clicked row:

 private void SomeGridMouseDown(object sender, MouseButtonEventArgs e)
    {
        var dependencyObject = (DependencyObject)e.OriginalSource;

        //get clicked row from Visual Tree
        while ((dependencyObject != null) && !(dependencyObject is DataGridRow))
        {
            dependencyObject = VisualTreeHelper.GetParent(dependencyObject);
        }

        var row = dependencyObject as DataGridRow;
        if (row == null)
        {
            return;
        }

        row.IsSelected = true;
    }

There are two solutions:

1. Set the width of the last column in the DataGrid to Width="*".
2. The second solution is a workaround. Add an additional empty column after the last column (i.e. neither setting its Header nor Binding properties) and set its width to Width="*"

I personally prefer the first solution; it's cleaner than the second one.