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.NET Forum / ASP.NET / General / March 2008page load after postback - how does it know?
Looking at the locals I have "ME" and "sender". I've just clicked on a dropdownlist and it's fired a post back. I'm in the page_load. I know that after the page_load is complete it will fire the click event handler for my dropdownlist, which indicates, since I've got several of these, that it knows which one fired. The question is: How does it know? Is there something in "Me" or "sender" that tells it what I clicked on? This seems to me to be a fairly rudimentary question, yet I'm not having any luck finding an answer via the usual search mechanisms. tia Chris > Looking at the locals I have "ME" and "sender". I've just clicked on a > dropdownlist and it's fired a post back. I'm in the page_load. I know [quoted text clipped - 9 lines] > tia > Chris When a page submits a form, .NET will implement the IPostBackEventHandler interface. This interface defines the RaisePostBackEvent method which is receiving the data from the control and will get fired when a postback is triggered. This method depends on the type of the control and will look up for an associated event handler to run it. See more in The ASP.NET Page Object Model article: http://msdn2.microsoft.com/en-us/library/aa479007.aspx its pretty simple. a control implements the IPostBackEventHandler interface. that control then renders some javascript that will do the postback. the javascript call includes the control name and arguments. this are stored in a hidden field, then a submit is done. on the server side, on a postback, if the postback event hidden field contains a value, it looks up the control with that id, and calls the IPostBackEventHandler method. the control then decides how to fire the event itself, and what to pass. -- bruce (sqlwork.com) > Looking at the locals I have "ME" and "sender". I've just clicked on a > dropdownlist and it's fired a post back. I'm in the page_load. I know [quoted text clipped - 9 lines] > tia > Chris
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