Windows Phone 7 TextBox.Height = auto in Code?

How can set the Textbox.Heig开发者_运维知识库ht to "auto" in Code? Thank you

I believe that Auto is Double.NaN

Update -

In addition to acceptable Double values, this property can also be Double.NaN. This is how you specify auto sizing behavior in code.

from http://msdn.microsoft.com/en-us/library/system.windows.frameworkelement.height.aspx