MVC how to return instruction to run javascript method?

Question

I am submitting an ajax form and returning a partialresult to the view. However, when validation fails I only want to tell the user why it failed with a js method without reloading the model for the view. How do I specify what to return in the controller?

Answer 1

I'd return a error text/html and check for that on success of the jQuery call and if it exists then just alert it out.

What might be nicer is if you return an error partial view and display that as a modal div giving the user a nice looking error message rather than just an alert.

for that matter you could return html/text and place that within a div on the page and simply show the div modal or otherwise.

i hate the simple alert messages from j/script. grey and ugly with a horrible ding sound. but that's just me.

EDIT

I'm going to make the assumption that you are going to return a partial view representing the error. This is I think the easiest and the best way.

Create an error object somewhere. Below is a very simple object. Add properties as required.

public class MyErrorObj
{
  public string errorText{get;set;}
}

Then in your controller you might have the following code. It assumes that you have a partial view called "ErrorDisplay" which inherits from MyErrorObj.

public ActionResult jQueryCheckError()
{
    MyErrorObj errObj = new MyErrorObj { errorText = "error happened" };
    return PartialView("ErrorDisplay", errObj);
}

Then in your view, not your partial view but your page;

$.post("/MyViewFolder/jQueryCheckError", { PARAMETERS GO HERE }, function(newErrorHTML) {
  $(".MyErrorDivContainer").html(newErrorHTML);
  $(".MyErrorDivContainer").html(newErrorHTML).slideDown(300);
});

The above posts to your controller action, then when it returns it uses the html that was returned and puts it into a div with a class name of "MyErrorDivContainer".

Now, you can check to see if the returned html is empty and then choose not to display the error message.

You could return a jSON object, itterate through the error collection and render the html to the same div if you wanted to. It's a little more involved but do-able.

Let me know if you want that code as well or if this is enough.

Answer 2

http://devlicio.us/blogs/billy_mccafferty/archive/2009/02/07/beware-of-asp-net-mvc-javascriptresult.aspx

public ActionResult DoSomething() {  
   script s = "$('#some-div').html('Updated!');";  
   return JavaScript(s);  
}  

But I'd suggest returning something like "Json(new { Type = "ValidationError", Errors = ModelState.SelectMany(x => x.Errors)})" - and process it on client side. Or, at least, wrap your returned JavaScript into common class, like "return new JavaScriptError(ModelState)".