Styling the indeterminate state of a WPF checkbox

Question

I want to style the indeterminate state of a WPF checkbox. We have a treeview control with checkboxes, and we want the indeterminate state to represent that some descendants are

Answer 1

You can use CheckBox styling from the classic theme located at:

• C:\Program Files (x86)\Microsoft Expression\Blend 4\SystemThemes\Wpf\classic.xaml

This implementation has a Path representing the checkbox mark called CheckMarkPath. I simply replaced this Path with a filled Rectangle to get these results: