Adding Select All Option in ComboBox Drop-Down

Version	Product	Author
6.7.0	Telerik UI for .NET MAUI ComboBox	Dobrinka Yordanova

Description

To add a Select All option in the dropdown list of a Telerik UI for .NET MAUI ComboBox, follow the steps below.

Solution

1. Define the HeaderTemplate for the ComboBox control. The HeaderTemplate should contain a CheckBox that represents the Select All option.

<telerik:RadComboBox 
    x:Name="comboBox"
    ItemsSource="{Binding Items}"
    SelectionMode="Multiple"
    IsEditable="True"
    DisplayMemberPath="Name"
    SelectedItems="{Binding SelectedItems}"
    AutomationId="comboSelectedItemMultiple"
    WidthRequest="200">
    <telerik:RadComboBox.HeaderTemplate>
        <DataTemplate>
            <HorizontalStackLayout>
                <telerik:RadCheckBox IsCheckedChanged="RadCheckBox_IsCheckedChanged"/>
                <Label Text="Select All"/>
            </HorizontalStackLayout>
        </DataTemplate>
    </telerik:RadComboBox .HeaderTemplate>
</telerik:RadComboBox >

2. Handle the IsCheckedChange event of the CheckBox in the HeaderTemplate. In the event handler, execute the ComboBox's SelectAllCommand when the checkbox is checked, and execute the ComboBox's ClearSelectionCommand when the checkbox is unchecked.

private void RadCheckBox_IsCheckedChanged(object sender, IsCheckedChangedEventArgs e)
{
    RadCheckBox cb = (RadCheckBox)sender;
    MyComboBox mcb = GetMyComboBox(cb);

    if (cb.IsChecked.HasValue && cb.IsChecked.Value)
    {
        mcb.SelectAllCommand.Execute(null);
    }
    else
    {
        mcb.ClearSelectionCommand.Execute(null);

    }
}

private static MyComboBox GetMyComboBox(Element element)
{
    if (element is MyComboBox myComboBox1)
    {
        return myComboBox1;
    }

    if (element == null)
    {
        return null;
    }

    return GetMyComboBox(element.Parent); //get ComboBox control recursively
}

That's it! You have successfully added a Select All option in the drop-down list of the ComboBox for .NET MAUI.

Next, customize the appearance of the Select All option to match your application's design.

If you want to use a command when the CheckBox state changes, review the Implementing the CheckBoxUserCommand Behavior When Migrating from Xamarin CheckBox to MAUI CheckBox how-to article.

See Also

• ComboBox Documentation