How to maintain the group expanded states while ungrouping and grouping the columns at runtime in WPF DataGrid (SfDataGrid)?

About the sample

This example illustrates how to maintain the group expanded states while ungrouping and grouping the columns at runtime in WPF DataGrid.

WPF DataGrid (SfDataGrid) allows you to maintain the expanded state of the group while ungrouping and grouping the columns at runtime by handling the events SfDataGrid.View.CollectionChanged, SfDataGrid.GroupExpanded and SfDataGrid.GroupCollapsed.

public Dictionary<string, bool> GroupStates = new Dictionary<string, bool>();

public MainWindow()
{
    InitializeComponent();
    this.dataGrid.Loaded += OnDataGrid_Loaded;
}

private void OnDataGrid_Loaded(object sender, RoutedEventArgs e)
{
    this.dataGrid.View.CollectionChanged += OnView_CollectionChanged;
    this.dataGrid.GroupExpanded += OnDataGrid_GroupExpanded;
    this.dataGrid.GroupCollapsed += OnDataGrid_GroupCollapsed;
}

private void OnDataGrid_GroupCollapsed(object sender, GroupChangedEventArgs e)
{
    GroupStates[e.Group.Key.ToString()] = false;
}

private void OnDataGrid_GroupExpanded(object sender, GroupChangedEventArgs e)
{
    GroupStates[e.Group.Key.ToString()] = true;
}

private void OnView_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
    var collectionViewWrapper = sender as GridQueryableCollectionViewWrapper;
    if (collectionViewWrapper != null)
    {
        if (collectionViewWrapper.Groups != null && collectionViewWrapper.Groups.Count > 0)
        {
            foreach (var group in collectionViewWrapper.Groups)
            {
                var grp = group as Group;
                var key = grp.Key.ToString();
                if (GroupStates.ContainsKey(key))
                {
                    grp.IsExpanded = GroupStates[key];
                    while (!grp.IsBottomLevel)
                    {
                        var innergroups = grp.Groups;
                        if (innergroups != null && innergroups.Count > 0)
                        {
                            foreach (var innerGroup in innergroups)
                            {
                                if (GroupStates.ContainsKey(innerGroup.Key.ToString()))
                                    innerGroup.IsExpanded = GroupStates[innerGroup.Key.ToString()];
                                else
                                    GroupStates.Add(innerGroup.Key.ToString(), innerGroup.IsExpanded);
                                grp = innerGroup;
                            }
                        }
                    }
                }
                else
                {
                    GroupStates.Add(key, grp.IsExpanded);
                }
            }
        }
    }
} 

KB article - How to maintain the group expanded states while ungrouping and grouping the columns at runtime in WPF DataGrid (SfDataGrid)?

Requirements to run the demo

Visual Studio 2015 and above versions.