Day Difference between two dates in VB.Net

in my asp.net+vb web  i am using this code to obtain the date diffrenec between two days

 im D1 As Date

Dim D2 As Date
Dim ts As New TimeSpan
D1 = txtHStart_Date.Text
D2 = txtHEnd_Date.Text
ts = D2 - D1

i want the diffrenec in a text box named difftxt.text

and another thing is =had kept a submit button to know the diffrence of both tetx boxes txtHstart and txtHend_date . Is there any other trick as when i enter the date in second text box ie 

txtHEnd_Date.text then the calculation starts and the diffrence is displayed in eifftxt.text