Problem regarding list box with check box in windows phone 8.1?

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C#

XAML

Windows-Phone-8

Hi,

I am developing a windows 8.1 application . For this I am in a need of list box with check boxes . I implemented all the code for this . My problem is I want to iterate the list box items . While doing this I am getting error like null reference exception.

My code is...

foreach(Classes.FilterOperators li in listOperators.Items)
                   {
                       ListBoxItem checedItem2 = this.listOperators.ItemContainerGenerator.ContainerFromItem(li) as ListBoxItem;
                       checedItem2.IsSelected = true;
                   }

I am getting the error in the loop at 2nd line.

I don't know how to iterate the loop any help...

Thanks.