ok, done it.
Protected Sub gvGridView_PreRender(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles gvDocsEmpresas.PreRender
For Each row As GridViewRow In gvGridView.Rows
Dim cbEscolhido1 As CheckBox = row.FindControl("cbEscolhido1")
Dim txtData1 As TextBox = row.FindControl("txtData1")
cbEscolhido1.Attributes.Add("onclick", "InsereData(this,'" + txtData1.ClientID + "');")
Next
End Sub
and then the Javascript
function InsereData(me, txtId)
{
var dt = new Date();
var nmonth = dt.getMonth();
var ntoday = dt.getDate();
var nyear = dt.getYear();
nmonth += 1;
var today = ntoday + "-" + nmonth + "-" + nyear;
if (me.checked)
{
document.getElementById(txtId).value = today;
}
else
{
document.getElementById(txtId).value = '';
}
}
with this, no postbacks :)