How to Select All CheckBox of a Column by DataGrid Header CheckBox in WPF DataGrid

Question

I have a DataGrid with one CheckBoxColumn. In the header of that CheckBoxColumn I have added a CheckBox to Select all CheckBoxes of that Datagrid Row.

How can I achi

Answer 1

It turns out that this is quite a lot harder to get right than one would hope.

The first problem is that you can't just bind the view model to the column header because it doesn't have the view model as its data context, so you need a binding proxy to correctly route the binding to the view model.

public class BindingProxy : Freezable
{
    public static readonly DependencyProperty DataProperty = DependencyProperty.Register(
        "Data", 
        typeof(object), 
        typeof(BindingProxy),
        new UIPropertyMetadata(null));

    public object Data
    {
        get { return this.GetValue(DataProperty); }
        set { this.SetValue(DataProperty, value); }
    }

    protected override Freezable CreateInstanceCore()
    {
        return new BindingProxy();
    }
}

Now create a binding proxy in your data grid's resources:

Then the column needs to be defined as:

Note that there needs to be a binding to both the check box's IsChecked dependency property and its Command property and the IsChecked binding is OneWay. The IsChecked binding gets the check box to display the current state of the items and the Command binding performs the bulk selection. You need both.

Now in the view model:

public bool? AreAllSelected
{
    get
    {
        return this.Items.All(candidate => candidate.IsSelected)
        ? true
        : this.Items.All(candidate => !candidate.IsSelected)
            ? (bool?)false
            : null;
    }

    set
    {
        if (value != null)
        {
            foreach (var item in this.Items)
            {
                item.IsSelected = value.Value;
            }
        }

        this.RaisePropertyChanged();
    }
}

And the SelectAllCommand property is an implementation of ICommand where the Execute method is:

public void Execute(object parameter)
{
    var allSelected = this.AreAllSelected;

    switch (allSelected)
    {
        case true:
            this.AreAllSelected = false;
            break;
        case false:
        case null:
            this.AreAllSelected = true;
            break;
    }
}

Finally your row item view models (i.e. the things in Items) need to raise PropertyChanged on the main view model each time the value of IsSelected changes. How you do that is pretty much up to you.