Sort and Group ListItems in a WPF ListBox- GroupItem collapse and expand

Question

I sort and group listbox items, I use CollectioView on this purpose.

From view model class I bind collection on ListBox ItemSource property, here is it.

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Answer 1

The workaround isn't perfect. As I said, it is better to use ViewModels with your own grouping, but it will require much more code.

You need two event handlers:

    private Dictionary<string, bool?> expandStates = new Dictionary<string, bool?>();

    private void Grid_Loaded(object sender, RoutedEventArgs e)
    {
        var grid = (Grid)sender;
        var dc = grid.DataContext as CollectionViewGroup;
        var groupName = (string)dc.Name;

        //If the dictionary contains the current group, retrieve a saved state of the group
        if (this.expandStates.ContainsKey(groupName))
        {
            var btn = (ToggleButton)grid.FindName("btnShowHide");
            btn.IsChecked = this.expandStates[groupName];
        } //Else add default state
        else this.expandStates.Add(groupName, true);

    }

    private void btnShowHide_Click(object sender, RoutedEventArgs e)
    {
        var btn = (ToggleButton)sender;
        var dc = (CollectionViewGroup)btn.DataContext;
        var groupName = (string)dc.Name;

        //Loaded event is fired earlier than the Click event, so I'm sure that the dictionary contains the key
        this.expandStates[groupName] = btn.IsChecked; //Save the current state
    }

They are bound with controls here:

<ControlTemplate TargetType="{x:Type GroupItem}">
    <Grid Loaded="Grid_Loaded">

and here:

<ToggleButton x:Name="btnShowHide" Click="btnShowHide_Click" IsChecked="True" Margin="3.5" />

If you define Template for GroupItem somewhere in an external dictionary, you must use UserControl for the purpose of having access to code-behind.