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Razor:

Templated delegates

The templated delegates functionality in Razor allows you to define a piece of markup and then have it used to represent a specific object on the page. This is a great tool when you need to represent e.g. one of your classes in multiple places inside of your View. It can also be a great way to separate a large chunk of markup from the logic of your View which can make it easier to read and maintain large Views.

When defining a templated delegate, you will be using a Func delegate - it could look like this:

Func<dynamic, object> movieTemplate = @<div>@item.Title [@item.ReleaseDate.ToShortDateString()]</div>;

In this first half, before the equal-sign, I create the movieTemplate delegate. In the second part, I specify the markup template to be used. Notice that I use a variable called item - it's passed into the delegate and the type is dynamic, meaning that I can access members on it (e.g. Title) which are not checked at compile-time. Instead, they are validated at runtime, where they are expected to exist on the object passed to the delegate - if not, an exception will be thrown! I intennd on passing in objects of the type Movie, a simple class we used previously in this tutorial:

public class Movie
{
    public string Title { get; set; }
    public DateTime ReleaseDate { get; set; }
}

So, with our templated delegate in place, we can now use it, e.g. inside a loop. Notice how I can now just call the delegate and pass in the Movie object, instead of defining the markup inside the loop:

@foreach(var movie in movies)
{
    @movieTemplate(movie)
}

When populating the movies collection, used in the loop, with some test data, the generated output will look like this:

<div>The Godfather [24-03-1972]</div>
<div>Forrest Gump [06-07-1994]</div>
<div>Fight Club [15-10-1999]</div>

And here's a complete example, including test data about movies, for you to experiment with:

@using HelloMVCWorld.Models
@{
    ViewData["Title"] = "TemplatedDelegate";

    Func<dynamic, object> movieTemplate = @<div>@item.Title [@item.ReleaseDate.ToShortDateString()]</div>;

    List<Movie> movies = new List<Movie>();
    movies.Add(new Movie() { Title = "The Godfather", ReleaseDate = new DateTime(1972, 3, 24) });
    movies.Add(new Movie() { Title = "Forrest Gump", ReleaseDate = new DateTime(1994, 7, 6) });
    movies.Add(new Movie() { Title = "Fight Club", ReleaseDate = new DateTime(1999, 10, 15) });

}

@foreach(var movie in movies)
{
    @movieTemplate(movie)
}

Summary

The templated delegates syntax found in Razor makes it easy for you to define markup-based templates which can be re-used in multiple places in your Views.

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