How do I make a checkbox tri-state?

At times, when you bind a checkbox to a table field that allows nulls, you may want the checkbox to have three states:

  • Selected
  • Unselected
  • Indeterminate

This is the default behavior for checkboxes added to DataGrids. However, if you want a standalone checkbox to have this behavior, you must set its ThreeState property to true.

The following image shows how each of these states is rendered in Windows Forms:

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