I have created HtmlHelper in ASP.NET MVC 4 razor view engine C#.
Can I pass view model property to my helper class?
For example, I have property
[Required]
[Display(Name = "Your Lastname")]
public string Lastname { get; set; }
Can I pass this property to my helper something like this @Html.Example(model => model.Lastname)
and then get data annotations in helper (if this field is required what is display name and etc.)?
The [Display]
attribute enriches the metadata. So you could fetch the information from the metadata.
For example if you wanted to retrieve the display name inside the helper:
public static class HtmlHelpers
{
public static IHtmlString Example<TModel, TProperty>(
this HtmlHelper<TModel> html,
Expression<Func<TModel, TProperty>> ex
)
{
var metadata = ModelMetadata.FromLambdaExpression(ex, html.ViewData);
var displayName = metadata.DisplayName;
return new HtmlString(html.Encode(displayName));
}
}
and then if we assume that you have a view model:
public class MyViewModel
{
[Required]
[Display(Name = "Your Lastname")]
public string Lastname { get; set; }
}
you could use the helper in your strongly typed view:
@model MyViewModel
@Html.Example(x => x.Lastname)
Now let's suppose that you wrote a custom metadata attribute:
public class FooBarAttribute : Attribute, IMetadataAware
{
public FooBarAttribute(string bar)
{
Bar = bar;
}
public string Bar { get; private set; }
public void OnMetadataCreated(ModelMetadata metadata)
{
metadata.AdditionalValues["foo"] = Bar;
}
}
that you used to decorate your model with:
public class MyViewModel
{
[Required]
[FooBar("This is the bar")]
public string SomeBar { get; set; }
}
and then inside your helper you could fetch the custom attribute:
public static class HtmlHelpers
{
public static IHtmlString Example<TModel, TProperty>(
this HtmlHelper<TModel> html,
Expression<Func<TModel, TProperty>> ex
)
{
var metadata = ModelMetadata.FromLambdaExpression(ex, html.ViewData);
if (metadata.AdditionalValues.ContainsKey("foo"))
{
var foo = metadata.AdditionalValues["foo"] as string;
return new HtmlString(html.Encode(foo));
}
return MvcHtmlString.Empty;
}
}
UPDATE:
It seems that you need to fetch the Required message. No idea why you need to do this in a custom helper but here's an example how you could achieve that:
public static class HtmlHelpers
{
public static IHtmlString Example<TModel, TProperty>(
this HtmlHelper<TModel> html,
Expression<Func<TModel, TProperty>> ex
)
{
var me = (ex.Body as MemberExpression);
if (me != null)
{
var required = me
.Member
.GetCustomAttributes(typeof(RequiredAttribute), false)
.Cast<RequiredAttribute>()
.FirstOrDefault();
if (required != null)
{
var msg = required.FormatErrorMessage(me.Member.Name);
return new HtmlString(html.Encode(msg));
}
}
return MvcHtmlString.Empty;
}
}