how to get run a function on textbox....

hi

 I have one procedure as below. I am using VS 2008 & sql server 2005

 public sub GetData(txt as string)

Ds = ClsgetData.GetFullData(txt)

if ds.tables(0).rows.count >0 then

GridView1.DataSource= ds
GridView1.DataBind()

end sub

now i Have one textbox on my webform. I want to be run this procedure onkeypress event with parameter of current textbox value.

i tried like but doent work

<asp:textbox runat="server" id=txtUsername onkeypress='<%=Getdata(this)%>' />

wiaitng for reply
...