The Problem

I have an application in WPF with a DataGrid that contains a checkbox column. I have a checkbox in the header to check and uncheck all the checkboxes in the column. That works well but I have been trying to get it unchecked after one of the checkboxes in the column is unchecked. I haven't been able to get the behaviour out of the code I have been writing for this situation that I want.

The Desired Behaviour

The column and DataGrid looks like:

DataGrid Checkbox Column

When the checkbox in the header is checked, all the checkboxes in the column become checked. And when the checkbox in the header is unchecked, all the checkboxes in the column become unchecked.

While the checkbox in the header is checked and all the checkboxes in the column are checked, if the user unchecks one of the checkboxes, the checkbox in the header should be unchecked.

Using the checked and unchecked events on the checkbox in the header works well to get the behaviour of checking and unchecking all the checkboxes contained in the column. But using them also causes issues when a single checkbox contained in the column is unchecked, because I want the checkbox in the header to be unchecked in that case which fires the unchecked event on the header checkbox causing every checkbox contained in the column to become unchecked.

The XAML for the CheckBox Column

                    <DataGridCheckBoxColumn Width="5*" 
                                            Binding="{Binding IsSelected, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}">
                        <DataGridCheckBoxColumn.HeaderTemplate>
                            <DataTemplate>
                                <CheckBox
                                    Name="CheckAll"
                                    Margin="2,0,0,0"
                                    HorizontalAlignment="Center"
                                    VerticalAlignment="Center"
                                    ClickMode="Press"
                                    IsChecked="{Binding CheckAllIsChecked, RelativeSource={RelativeSource AncestorType=Window}}"
                                    Checked="CheckAll_Checked"
                                    Unchecked="CheckAll_Unchecked"
                                    />
                            </DataTemplate>
                        </DataGridCheckBoxColumn.HeaderTemplate>

                        <DataGridCheckBoxColumn.ElementStyle>
                            <Style TargetType="{x:Type CheckBox}">
                                <Setter Property="HorizontalAlignment" Value="Center" />
                                <Setter Property="ClickMode" Value="Press" />
                                <EventSetter Event="Checked" Handler="DataGridCheckBox_Checked" />
                                <EventSetter Event="Unchecked" Handler="DataGridCheckBox_Unchecked" />
                            </Style>
                        </DataGridCheckBoxColumn.ElementStyle>
                    </DataGridCheckBoxColumn>

The Event Code

    private void DataGridCheckBox_Checked(object sender, RoutedEventArgs e)
    {
        UpdateCheckAllIsChecked();
    }

    private void DataGridCheckBox_Unchecked(object sender, RoutedEventArgs e)
    {
        UpdateCheckAllIsChecked();
    }

    private void CheckAll_Checked(object sender, RoutedEventArgs e)
    {
        UpdateCheckBoxes();
    }

    private void CheckAll_Unchecked(object sender, RoutedEventArgs e)
    {
        UpdateCheckBoxes();
    }

    /// <summary>
    /// Updates the CheckAll checkbox to indicate whether all files are selected.
    /// </summary>
    private void UpdateCheckAllIsChecked()
    {
        if (FilesDataGrid.ItemsSource is List<FileDetail> fileDetails)
        {
            CheckAllIsChecked = fileDetails.All(f => f.IsSelected);
        }
    }

    /// <summary>
    /// Updates the IsSelected property of all files in the DataGrid control to set the checkboxes that 
    /// represent them.
    /// </summary>
    private void UpdateCheckBoxes()
    {
        if (FilesDataGrid.ItemsSource is List<FileDetail> files)
        {
            foreach (var file in files)
            {
                file.IsSelected = CheckAllIsChecked;
            }
        }
    }

To fix the problem, I tried to use the MouseUp event on the checkbox in the header but the event never fired which stopped the behaviour of checking and unchecking all checkboxes contained in the column.

What can I do to get the behaviour I desire from the checkbox column in the DataGrid?