Templated delegates

La fonctionnalité de modèles délégués dans Razor vous permet de définir un ensemble de balises et ensuite de l'utiliser pour représenter un objet spécifique dans la page. C'est un bon outil lorsque vous avez besoin de représenter, par exemple, une de vos classes dans divers endroits de votre Vue. Cela peut également être un bon moyen de séparer un gros morceau de balises depuis la logique de votre Vue, ce qui peut le rendre plus simple à lire et à maintenir.

Lors de la définition d'un template de délégué, vous serez amené à utiliser un délégué Func - cela ressemblera à ceci:

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 intend 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.