How to put this validation on asp.net file upload control?

I have a fileUpload User Control FileUploadControl.ascx containing asp.net fileupload control and a requiredfield validator.

I have another usercontrol RenderingTemplate.ascx that contains two FileUploadControl.ascx.

RenderingTemplate.ascx is on page RenderingTemplateDetails.aspx, this page has save and cancel button.

Now My requirement is in case user selects a file in one fileupload control,he has to select in other as well. If he does not select any file,let postback happen.

I cannot use Requiredfieldvalidator as it fires for both. I tried adding onclientclick to page save button and check whether file upload has some text in it.but i didnot succedd.

Now i want this functionality to be a part of control so that i dont have to recode it on every page. IS there any clientside 开发者_StackOverflow社区event on usercontrol which fires when save button of page is clicked. Please help and suggest some solution.

The solution will become easier if you add custom validator. Take a look at how to add client validation function to custom validator.

Add custom validator to both of the file uploads and then in client validation function, place a single javascript function, Here is a simple example:

function ValidateUpload(source,args){
   //assume f1 and f2 are your file upload controls:
   var f1 = document.getElementById('f1'); //in case of asp.net control use clientID
   var f2 = document.getElementById('f2');
   if(f1.value == f2.value)
     args.IsValid = true;
   else
     args.IsValid = false;
}

Notes: you can use single custom validator as well, or you can use source and args.Value with some additional logic to solve this but I think this is the most simple implementation I find.