command is not firing when IsChecked binding changed programmatically

Hi,

I have a checkbox added to treeview item.

In the heirarchicaldatatemplate, i have binded checkbox's isChecked property and command property to class properties.

when i press the checkbox with mouse, the command fires. but when i programatically set IsChecked property, the command doesnt fires.

i have checked in net, even in msdn forum, its suggested the following in forum.

"You can manually raise the command's CanExecuteChangedevent to notify the command source, or you can call CommandManager.InvalidateRequerySuggested method to force CommandManager to raise the RequerySuggested event."

But i am not exactly getting where to raise CanExecuteChanged or call CommandManager.InvalidateRequerySuggested method?

My code:

<HierarchicalDataTemplate x:Uid="HierarchicalDataTemplate_1" x:Key="1" ItemsSource="{Binding Models}">

           <CheckBox x:Uid="CheckBox_1" ClickMode="Press" IsChecked="{Binding Path=IsChecked,Mode=TwoWay}"                     

                     Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:HComboBox}}, Path=CheckAll, Mode=TwoWay}" CommandParameter="{Binding}">

               <TextBlock x:Uid="TextBlock_1" Text="{Binding Caption}"></TextBlock>

           </CheckBox>

       </HierarchicalDataTemplate>

publicICommand CheckAll

       {

           get { return (ICommand)GetValue(CheckAllProperty); }

           set { SetValue(CheckAllProperty, value); }

       }

publicstaticreadonly DependencyProperty CheckAllProperty =

           DependencyProperty.Register("CheckAll",typeof(ICommand),typeof(HComboBoxCopy),newUIPropertyMetadata(null));

public HComboBoxCopy()

{

    InitializeComponent();

    this.CheckAll =newDelegateCommand<Object>(ItemChecked);

}

publicvoid ItemChecked(Object e)

{ //Code }