Dynamic input in Templated Razor Delegates - ASP.Net Core Razor Pages

Question

Hello,

The input parameter in the following Templated Razor Delegate is dynamic. I expected I didn't have any errors before executing the program. because it is a dynamic type and it execute at run time if we misspell the name.

@page
@model WebApplication1.Pages.WelcomeModel
@{
     Func<dynamic, object> myUnorderedListTemplate =
               @<ul>
               @foreach (var item in cities)
               {
                    <li>@item.Name</li>
               }
     </ul>;
}
@myUnorderedListTemplate(citiesA) @*when added A to cities, the compiler got an error. 
            The variable is dynamic and I did not expect the error before execution.*@
@functions {
     public class City
     {
          public string Name { get; set; }
          public string Country { get; set; }
     }
     List<City> cities = new List<City>{
        new City { Name = "London", Country = "UK" },
        new City { Name = "Paris", Country = "France" },
        new City { Name = "Rome", Country = "Italy" }
    };
}

Answer 1

The loop pattern is...

Func<dynamic, object> myUnorderedListTemplate =
    @<ul>
    @foreach (var i in item)
    {
        <li>@i.Name</li>
    }
    </ul>;

Answer 2

dynamic is similar to object in that its type can be changed. what's different is that the properties and methods are executed at runtime via reflection.

in your code:

Func<dynamic, object> myUnorderedListTemplate =
     @<ul>
     @foreach (var item in cities). 
     {
         <li>@item.Name</li>
     }
     </ul>;

you have a couple of issues:

• the variable cities is not a parameter, just a undefined variable.
• also the razor html syntax is not supported in a function definition.

while a helper is cleaner, you can:

Func<IEnumerable<dynamic>, HtmlString> myUnorderedListTemplate = (cities) =>
{
    var html = "<ul>";
    foreach (var item in cities)
    {
       html += $"<li>{System.Web.HttpUtility.HtmlEncode(item.Name)}</li>";
    }
    html += "</ul>";
    return new HtmlString(html);
};

though as the function needs to know the property names, not sure why dynamic.

in your code calling the function the variable citiesA is undefined.

@myUnorderedListTemplate(citiesA)

Answer 3

Hi @Shervan360 ,

Func<dynamic, object>

The input parameter represents data and is a dynamic type, the data is accessible within the template through a parameter named item. When you pass citiesA, you need to define citiesA first, the full code like :

@page
@model WebApplication1.Pages.WelcomeModel
@{
     Func<dynamic, object> myUnorderedListTemplate =
               @<ul>
               @foreach (var city in item)
               {
                    <li>@city.Name</li>
               }
     </ul>;
}
@myUnorderedListTemplate(citiesA) @*when added A to cities, the compiler got an error. 
            The variable is dynamic and I did not expect the error before execution.*@
@functions {
     public class City
     {
          public string Name { get; set; }
          public string Country { get; set; }
     }
     List<City> cities = new List<City>{
        new City { Name = "London", Country = "UK" },
        new City { Name = "Paris", Country = "France" },
        new City { Name = "Rome", Country = "Italy" }
    };
    List<City> citiesA = new List<City>{
        new City { Name = "London", Country = "UK" },
        new City { Name = "Paris", Country = "France" }        
    };
}

result:

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