Adding a 'ValueChangedOnPostback' property to TextBox, DropDownList, CheckBox, RadioButton, etc.

For my current project I'm building a framework that automatically saves all form-data on a page postback. Because a save-operation is time consuming, I want the framework only to save the information when the user really changed the data on the page.

For this, the ASP.NET framework offers a 'changed' event for each editor (TextBox, DropDownList, etc.) . E.g. when a user has changed the value in a textbox, the TextChanged event will be fired somewhere after the Page_Load and before the Page_OnPreRender event. This basically was my problem: I needed to know if the textbox was changed in the Page_Load eventhandler, not after. The TextChanged event of the TextBox just fired to late for me.

My solution was to write my own edit-controls that all inherited from their corresponding System.Web.UI.WebControls classes. All my custom edit-controls implement the IPostBackDataHandler interface, so the ASP.NET framework will call the LoadPostData method somewhere between the Init and the Load event. Also, I added my own IPostBackDataChanged interface, containing the boolean property 'ValueChangedOnPostback'. This property I can now read on the Page_Load event to know if the data of the TextBox was changed by the user.

Example code for my custom TextBox:

namespace MyProject.Web.UI.WebControls
{
   public class TextBox : System.Web.UI.WebControls.TextBox, IPostBackDataHandler, IPostBackDataChanged
   {
      private bool _valueChangedOnPostback = false;
      public bool ValueChangedOnPostback
      { 
         get { return _valueChangedOnPostback; }
      }

      bool IPostBackDataHandler.LoadPostData(string postDataKey, NameValueCollection postCollection)
      {
         string text1 = this.Text;
         string text2 = postCollection[postDataKey];
         if (!text1.Equals(text2))
         {
            this.Text = text2;
            _valueChangedOnPostback = true;
         }
         return _valueChangedOnPostback;
      }
      void IPostBackDataHandler.RaisePostDataChangedEvent()
      {
         this.OnTextChanged(EventArgs.Empty);
      }
   }
}