根据需要/不需要字段进行WPF验证

I'm new to WPF's developing but I was thinking about how to kill 3 birds with one stone. Example: I've a form with 2 TextBox and 2 TextBlocks. The first 'bird' would be to be able to "enrich" some textblock with an asterisk if they refer to required fields:I'm new to WPF's developing but I was thinking