Question

I’m having hard time understanding the following C# code. This code was taken from Pro ASP.NET MVC 2 Framework by Steven Sanderson. The code esentially creates URLs based on a list of categories.

Here’s the code:

        Func<string, NavLink> makeLink = categoryName => new NavLink { 
            Text = categoryName ?? "Home", 
            RouteValues = new RouteValueDictionary(new { 
                controller = "Products", 
                action = "List", 
                category = categoryName, 
                page = 1 
            }),
            IsSelected = (categoryName == currentCategory)

A lot of stuff is going on here. I’m guessing it’s defining a function that expects two parameters of type string, and NavLink. Then I see the Lambda categoryName => new NavLink etc.... I think all it’s doing is creating an instance of NavLink.

The function is then called in the same Controller action:

        // Place home link on top
        List<NavLink> navLinks = new List<NavLink>();
        navLinks.Add(makeLink(null));

        // Add link for each distinct category
        var categories = productsRepository.Products.Select(x => x.Category.Name);
        foreach (string categoryName in categories.Distinct().OrderBy(x => x))
            navLinks.Add(makeLink(categoryName));

I can tell that it’s making a list of NavLink. I don’t understand why Steven Sanderson wrote it this way though. Couldn’t he have written something like:

var categories = productsRepository.Products.Select(x => x.Category.Name);
foreach (string categoryName in categories.Distinct().OrderBy(x => x))
{
    var newlink = new Navlink{
        text = categoryName,
        RouteValues = new RouteValueDictionary(new {
           controller = "Products",
           action = "List",
           category = categoryName,
           page = 1
        }),
        IsSelected = (categoryName == currentCategory)
    }
    navLinks.Add(newlink);
}

Is there an advantage to doing it Steven’s way versus my way?

Answer 1

It looks like that he wanted to use a local function that can be used for both adding the home link and as part of the categories loop. If he did it in-line like you did he would have to almost repeat the same code just for the single home link.