在ASP.NET MVC中，为什么绑定到对象而不是特定类型时将参数绑定为数组

Question

I have a bunch of controllers with a similar delete action, so I'm putting that into a base class. This is what it looked like before:

    public async Task<ActionResult> Delete(int id)
    {
        await apiClient.Delete(id);
        return new EmptyResult();
    }

And in the view there's a raw link pointing to:

/Items/Delete?Id=" + item.Id

And that works fine, but then some of the models use a string as a key in place of int. Since the API client is backed by an Entity Framework repo which can delete by object , I just tried this:

    public async Task<ActionResult> Delete(object id)
    {
        await apiClient.Delete(id);
        return new EmptyResult();
    }

Now I am getting a single-element array bound to id . The single element is the string representing the item.Id . Why's that? Why it's an array and not simply the element?

Answer 1

My guess is that's actually the default format for data passed to it, since all form values are passed to the server as string, and when there are name collisions, the values are accessible as an array under that name. So really, string[] is the default type of all submitted values, and anything else involves some kind of automatic conversion.

For example, if you had a form with three text inputs that all had the same name "text", the browser would send all three, and MVC would start out with a string array called "text". Since the controller parameter type is 'object', it really can't make any smart guesses about what to do with it, so it just gives you the original array.

On the other hand, if the field type is known to be string, then it combines them into a comma separated list; and you could probably avoid such an unwanted concatenation step by setting the type to 'string[]'. If the parameter type is 'int', it tries to convert the string value to an integer. If the parameter type is 'bool', it will try to interpret the string as a Boolean. So, the string array is actually the normal value, and it's everything else that's receiving special transforms.