error in using BtnSubmit.Attributes("onclick") in asp.net

can anybody tell me what is problem in

BtnSubmit.Attributes("onclick") = string.Format("document.getElementById(\'{0}\').value= document.getElementById(\'{1}\').value;", this.HiddenField1.ClientID, this.FileUpload1.ClientID)开发者_开发知识库;

it is giving me error 'Non invocable memberusing System.Web.UI.WebControls.Attributes cannot be used like method.'

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Please use Attributes properly. As it's an readonly property you can use it like this:

BtnSubmit.Attributes.Add("onclick", string.Format("document.getElementById(\'{0}\').value= document.getElementById(\'{1}\').value;", this.HiddenField1.ClientID, this.FileUpload1.ClientID));