WPF label and textbox width

Hello,

Whenever I change my textbox/label from the code behind, the width doesn't update until my function stops running.

For example:

if label.content="test"

and the width returned was 50,

then I change the content to "test test"

I would still get 50 as width unless I restart this function.

Why doesn't the width change when I change the content?

How can I change the width immediately according to the content?

Thanks.