While uploading large files, it is nice to have a “Please wait…” text displaying on the button. You can simple achive this using ClientScript.GetPostBackEventReference method.
this.uxUpload.Attributes.Add("onclick", "this.value='Uploading... please wait'; this.disabled=true;" + ClientScript.GetPostBackEventReference(this.uxUpload,""));
The GetPostBackEventReference injects the __doPostBack method and also the hidden fields that hold the event target and event arguments.
This is a useful technique when uploading large files and during the process disabling the button control.
