How do I call textbox change even when button is clicked?

See more:

C#

ASP.NET

Hi,

I have a gridview that has a column with a calender button and a textbox, when the button is clicked the popup for the calender control shows and when the user selects a date the textbox is populated with the date, I now have a change request so that when a user selects a date then the rest of the textboxes for the rest of the columns must get the same value.

I have tried using on text change but it does not fire until I go edit the textbox by pressing keys.

here is my code:

when the button is clicked:
btnPOPDropEnd.OnClientClick = "popCalendar('" + txtDropEnd.ClientID + "', '" + pnlPOPDropEnd.ClientID + "', '" + dateTestEnd + "'); return false;";

when setting the value:
updateCalendar(text_box, pop_div, currentDate);

how can i set the rest of the textbox values to the same date when this button assigns the date to 1 of the textboxes?

thanks