Error Handling on Controller

Question

In my MVC application, I use uploadify for file uploads. The controller action is:

[HttpPost]
public ActionResult Upload(HttpPostedFileBase fileData, FormCollection forms)
{
  try
  {                
    if (fileData.ContentLength > 0)
    {
      var statusCode = Helper.UploadList();
      if (statusCode.Equals(System.Net.HttpStatusCode.Created))
      return Json(new { success = true });                      
    }                  
  }
  return Json(new { success = false });        
}
catch (Exception ex)
{       
}   

I set success= true/false based on the StatusCode and pass it to the onComplete event of uploadify (in a .js file) and show some meaningful alerts.

If Helper.UploadList() throws an exception like:

throw new ArgumentException("Doesn't exist");   

How can I catch that exception in the controller action and eventually pass it to the .js file so that I can show an error to the user?

EDIT: If I set return Json(new { success = false }); in the catch block, the value doesn't reach the onComplete.

'onComplete': function (event, queueID, fileObj, response, data) {
                if (response == '{"success":true}') {                    
                    alert("file uploaded successfully.");
                }
                else if (response == '{"success":false}') {
                    alert('file failed to upload. Please try again!');                   
                }
                return false;
            },

    I see this on the UI:

Answer 1

you can do this a little smarter :

public class ErrorModel{
    public bool Success{get;set;}
    public string Reason{get;set;}
}

public JsonResult Upload(HttpPostedFileBase fileData, FormCollection forms)
 {
    var model = new ErrorModel { Success = false };
    try
 {                
    if (fileData.ContentLength > 0)
  {
     var statusCode = Helper.UploadList();
    if (statusCode.Equals(System.Net.HttpStatusCode.Created))
    model.Reason = "File uploaded: " + filename;
    model.Success = true;
    return JSon(model);                           
   } else {
     model.REason = "ERROR: failed to upload file";
     return JSon(model);  
   }                  
 }

   }
    catch (Exception ex)
  {  
 model.reason = ex.Message;
 return JSon(model);  
}   

javascript:

dataTYpe: 'json',
success: function(data){
     if(data.Success){
       } else {
         alert(data.Reason);
      }
}

needs a little extra work and you need to do more checking on your file, but you will find it easier to return meaningful results this way.

Answer 2

you might consider returning a status code

catch(Exception ex)
{
    return new HttpStatusCodeResult(400, "Unexpected error uploading");
}

in your js

$.ajax({
    url: "http://blaa.com/Upload",
    type: "post",
    statusCode: {
        400: function(e) {
            // do whatever
        }
    }
});

the message can be found in e.statusText, but you must be using IIS or IIS Express to see it, the VS dev server does not send it when debugging - http://forums.asp.net/post/4180034.aspx