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Strongly Typed Custom HTML Helpers In MVC

In the previous article ‘Custom HTML helpers in MVC’ we learned how to create custom HTML Helpers. In this article we will learn how to create strongly typed custom HTML Helpers. 

To create a strongly typed helper we need to understand what makes them different from regular HTML Helpers. Strongly typed helpers are used to pass data from the model to the helper using expression syntax. The ‘HtmlHelper<TModel>’ class is a strongly typed subclass of the ‘HtmlHelper’ class.

Creating Strongly Custom Helper

To create a strongly typed custom helper we writethe extension method for ‘HtmlHelper<TModel>’ class. We also use the following:

  1. Expression:

    While using a strongly typed helper on view we use lambda expressions like ‘@Html.TextBoxFor(m=>m.Name)’. Expression class is used to get the model information from this lambda expression.

  2. ModelMetaData:

    This class is used to get model information with its data from the lambda expression.

    Example:

    Add new class in MVC application and give it a meaningful name. Add one model class as User as in the following:
    1. public class User  
    2. {  
    3.    public string UserName { get; set; }  
    4. }  

In this application add class “CustomHelper”. As we are going to createan extension method make this class static. Write the following code in class.

  1. using System;  
  2. using System.Linq.Expressions;  
  3. using System.Web.Mvc;  
  4. namespace StrongCustomHelpers  
  5. {  
  6.     public static class CustomHelper  
  7.     {  
  8.         public static MvcHtmlString CustomTextBoxFor < TModel, TProperty > (this HtmlHelper < TModel > htmlHelper, Expression < Func < TModel, TProperty >> expression)  
  9.         {  
  10.             var name = ExpressionHelper.GetExpressionText(expression);  
  11.             var metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);  
  12.             TagBuilder tb = new TagBuilder("input");  
  13.             tb.Attributes.Add("type", "text");  
  14.             tb.Attributes.Add("name", name);  
  15.             tb.Attributes.Add("value", metadata.Model as string);  
  16.             tb.Attributes.Add("style", "color:red");  
  17.             return new MvcHtmlString(tb.ToString());  
  18.         }  
  19.     }  
  20. }  
Inthe above code we created a static method CustomTextBoxFor for HtmlHelper<TModel> class. In this method we created an HTML tag with the help of TagBulider class. We get the name of the model’s property with the help of ‘GetExpressionText()’ method of ‘Expression’ class. This name is used as the Id for the helper element on view. We get model data with the help of ‘FromLambdaExpression()’ method. And then use this data as a value forthe helper element. We also set the forecolor of text input to red.

Now we can use this helper on view as below:

helper on view

Add this helper to view for UserName property as below:

Html.CustomTextBoxFor(m=>m.UserName)
Run application and check output.

run

Advantages of creating custom helpers

The advantage of custom helper is that suppose we create a helper with some style attributes or other properties. Then we don’t need to write the same code on multiple views for those properties. We just need to add custom helper. Like in the above example, we createa  text field with red forecolor. So when we need a text field with a red color we don’t need to write style, we just use this new helper instead of the inbuilt helper.

Conclusion

In this article we learned to create strongly typed custom HTML Helpers. This will help us to remove some redundant code from the application.
 
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