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asp.netcode-behindautopostback

Why do I have to force an AutoPostBack="true"?

ASP.net 2.0, Visual Studio 2005, and standard controls such as <asp:DropDownList>, etc require that I put in AutoPostBack="true" for there to be a call to the code behind. But why? Shouldn't that be happening anyway? Thanks

Solution

  • Code behind runs on the server. HTML code and Javascript run on the browser.

    A dropdownlist is an HTML element that runs on the browser. It can't do anything on the server without sending data back to the server. The means by which ASPX web forms send data to the server is via postback.

    Sometime you don't want a dropdownlist to send data to the server. It really slows down the user experience to have to wait for something to cross the wire. To speed things up, you can disable the postback on the list control; the server will only get contacted when the user posts the whole form. At that point, the server can inspect the list control to see if its value has changed and take action.