WPF Select all CheckBox in a DataGrid

Question

I'm trying to select all CheckBox in a DataGrid but I didn't get any result using this code bellow

This is the function that I'm calling when the main CheckBox is clicked

private void CheckUnCheckAll(object sender, RoutedEventArgs e)
{
    CheckBox chkSelectAll = ((CheckBox)sender);
    if (chkSelectAll.IsChecked == true)
    {
        dgUsers.Items.OfType<CheckBox>().ToList().ForEach(x => x.IsChecked = true);
    }
    else
    {
        dgUsers.Items.OfType<CheckBox>().ToList().ForEach(x => x.IsChecked = false);
    }
}

dgUsers is the DataGrid but as I realize any checkbox is found.

This is the XAML that I'm using tho create the CheckBox in the datagrid

<DataGrid.Columns>
    <DataGridCheckBoxColumn x:Name="col0" HeaderStyle="{StaticResource ColumnHeaderGripperStyle}">
         <DataGridCheckBoxColumn.HeaderTemplate>
              <DataTemplate>
                   <CheckBox Click="CheckUnCheckAll" >
                   </CheckBox>
              </DataTemplate>
         </DataGridCheckBoxColumn.HeaderTemplate>
    </DataGridCheckBoxColumn>
<DataGrid.Columns>

And this is the picture of my DataGrid

Is there some way to select all checkbox programatically ?

Edit I already tried to follow this steps

that you can see that my code is the same there but didn't work to me

Answer 1

TLDR; This is what you want, code below:

The proper place to do this would be in your ViewModel. Your CheckBox can have three states, all of which you want to make use of:

1. Checked - Every item is checked
2. Unchecked - No item is checked
3. Indeterminate - Some items are checked, some are not

You will want to update the CheckBox whenever an item is checked/unchecked and update all items whenever the CheckBox was changed - implementing this only one way will leave the CheckBox in an invalid state which might have a negative impact on user experience. My suggestion: go all the way and implement it properly. To do this you need to be aware of which caused the change - the CheckBox of an entry or the CheckBox in the header.

Here is how I would do it:

First you need a ViewModel for your items, I've used a very simplified one here that only contains the IsChecked property.

public class Entry : INotifyPropertyChanged
{
    private bool _isChecked;

    public bool IsChecked
    {
        get => _isChecked;
        set
        {
            if (value == _isChecked) return;
            _isChecked = value;
            OnPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

Your main ViewModel will have a collection of all items. Whenever an item's IsChecked property changes, you'll have to check if all items are checked/unchecked and update the CheckBox in the header (or rather the value of its datasource).

public class ViewModel : INotifyPropertyChanged
{
    public List<Entry> Entries
    {
        get => _entries;
        set
        {
            if (Equals(value, _entries)) return;
            _entries = value;
            OnPropertyChanged();
        }
    }

    public ViewModel()
    {
        // Just some demo data
        Entries = new List<Entry>
        {
            new Entry(),
            new Entry(),
            new Entry(),
            new Entry()
        };

        // Make sure to listen to changes. 
        // If you add/remove items, don't forgat to add/remove the event handlers too
        foreach (Entry entry in Entries)
        {
            entry.PropertyChanged += EntryOnPropertyChanged;
        }
    }

    private void EntryOnPropertyChanged(object sender, PropertyChangedEventArgs args)
    {
        // Only re-check if the IsChecked property changed
        if(args.PropertyName == nameof(Entry.IsChecked))
            RecheckAllSelected();
    }

    private void AllSelectedChanged()
    {
        // Has this change been caused by some other change?
        // return so we don't mess things up
        if (_allSelectedChanging) return;

        try
        {
            _allSelectedChanging = true;

            // this can of course be simplified
            if (AllSelected == true)
            {
                foreach (Entry kommune in Entries)
                    kommune.IsChecked = true;
            }
            else if (AllSelected == false)
            {
                foreach (Entry kommune in Entries)
                    kommune.IsChecked = false;
            }
        }
        finally
        {
            _allSelectedChanging = false;
        }
    }

    private void RecheckAllSelected()
    {
        // Has this change been caused by some other change?
        // return so we don't mess things up
        if (_allSelectedChanging) return;

        try
        {
            _allSelectedChanging = true;

            if (Entries.All(e => e.IsChecked))
                AllSelected = true;
            else if (Entries.All(e => !e.IsChecked))
                AllSelected = false;
            else
                AllSelected = null;
        }
        finally
        {
            _allSelectedChanging = false;
        }
    }

    public bool? AllSelected
    {
        get => _allSelected;
        set
        {
            if (value == _allSelected) return;
            _allSelected = value;

            // Set all other CheckBoxes
            AllSelectedChanged();
            OnPropertyChanged();
        }
    }

    private bool _allSelectedChanging;
    private List<Entry> _entries;
    private bool? _allSelected;
    public event PropertyChangedEventHandler PropertyChanged;

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

Demo XAML:

<DataGrid ItemsSource="{Binding Entries}" AutoGenerateColumns="False" IsReadOnly="False" CanUserAddRows="False">
    <DataGrid.Columns>
        <DataGridCheckBoxColumn Binding="{Binding IsChecked, UpdateSourceTrigger=PropertyChanged}">
            <DataGridCheckBoxColumn.HeaderTemplate>
                <DataTemplate>
                    <CheckBox IsChecked="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=local:MainWindow}, Path=ViewModel.AllSelected}">Select All</CheckBox>
                </DataTemplate>
            </DataGridCheckBoxColumn.HeaderTemplate>
        </DataGridCheckBoxColumn>
    </DataGrid.Columns>
</DataGrid>