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Asp.net TagHelper to add a class depending on an expression (inspired by Angular)

I am thinking about to create an tagHelper-attribute in the way of Angular.
In Angular I can do following:
<div [class.extra-sparkle]="isDelightful"></div>
This binds an css-class extra-sparkle depending on the bool-expression isDelightful to the div-tag.
I was thinking about to to the same in asp.net core mvc.
1. Idea
My first thought was to do it like this, but in this way the attribute-part 'myClass' has to be defined in a kind of wildcard attribute like 'myPrefix-*'.
But so far i saw there is no wildcard-option.
<div myPrefix-myClass="(expression)"></div>
2. Idea
My second idea was to use an attribute type of Func-Delegate.
<div myPrefix-class-if="("myClass", Model)=> Model.x == true"></div>
But in this case I'm struggeling with the razor-syntax and I also don't know,
whether it's possible to use a Func-Delegate as an property within a taghelper.
Does anybody know a possible solution or have an idea?

Using model objects in cshtml file

I am a newbie to MVC 4, (after 10 yrs of webforms) and have a question that I have not been able to figure out.
When writing code in the cshtml file, I am walking through a tutorial that has the following line:
#Html.DisplayNameFor(model => model.City)
What does the model => model.City imply? Why can't I use #Html.DisplayNameFor(model.City) ? I understand this is Linq query, but I would like to understand why would I need the model goes to model.city ?

Generally, that is called a lambda expression.In your scenario, you are telling the DisplayNameFor method that "take my model, and create a display element for this property.".You can't use model.City, because it just returns the value of the property.The method needs more than that in order to create a display element for your property.For example, it needs to know it's type and also it's attributes (like DisplayName attribute) and then it creates a display element for your element(it should be label I guess) .
DisplayName method is doing that using Expression Trees.The method takes an Expression<Func<TModel, TValue>> and uses it to get the name, value and the metadata information (attributes) about your property.
If you want to use model.City you can still use it, but then you won't need the functionality that DisplayNameFor provides.If you just need to display value of the property you can always do it like this:
<label> #model.City </label>
I understand this is Linq query,
Btw, this is incorrect, that is not a LINQ query.That is just an extension method.

Write additional HTML comments in razor

I'm struggling with the following problem and I can't find an acceptable way to solve it.
My challenge: write out HTML comments just before the actual property value in a Razor view.
This is my (simplyfied) Viewmodel:
public class Article
{
public string Title {get;set;}
}
To write out this title I simply do this in my Razor view:
<h2>#Model.Title</h2>
Now I want to write out a html comment just before the actual title so the generated HTML looks like this (simplyfied):
<h2><!-- some parameters for a 3th party system --> This is my title</h2>
The HTML comment comes from an Attribute I applied to the 'Title' attribute. It's value is generated, so the attribute-value is added at runtime using the TypeDescriptor from the .NET framework.
Now I know I could achieve this by simply writing out all my properties using an HTML helper. Like this: #MyHelper.Write(m => m.Title)
But since potentially ALL my properties need this HTML comment I want to avoid the use of an HTML helper since it clutters the View and doesn't make the view look nice and (more) readable.
This is what I have tried:
Created a custom Razor base page (Inheriting from WebViewPage<TModel>). And overwriting it's 'Write' method.
This kind of works but the BIGGEST problem here is that I don't know which property is been written out at that moment. There is no way of getting the current property name in the 'Write' method. So now I dynamically search my Model to find a property with the value that's been written out and prepend the HTML comment from the attribute.
My question: is there another approach to accomplish what I want. As sais before: I want to avoid using an HTML helper to write out all my properties. (Think about loops, etc. It's just not nice).
Also, adding this HTML comment in my Controller is no option since:
it's not part of the actual value. Is a sort of metadata.
The HTML comment should be added to int's, double's and DateTime's. There is no way to adjust a double property to include a string. (Image a List<DateTime>. All date's need this HTML comment)
the HTML comment should be added based on a web.config setting. Yes or No. (The actual HTML comment is different for each value of a property)
I realize this question is rather long. Sorry for that. Any thoughts are appreciated.

You can use the existing #Html.Raw(Model.Title)
Alternatively you can use a display templates. Add a UIHintAttribute to the properties you wish to behave this way.
public class MyModel
{
[UIHint("Raw")]
public string MyString { get; set; }
}
Create a new display template called Raw.cshtml that accepts model of type string:
#model string
#Html.Raw(model)
Then in your view you can use:
#Html.DisplayFor(m => m.MyString)
This still requires that you use a helper (DisplayFor). This is a recommended practice that allows you to easily change the behavior of one or many fields with minimal code changes.

Adding HTML5 data attributes to System.Web.Helpers.WebGrid [duplicate]

I am using an MVC3 WebGrid, and want to add custom attributes of the form "data-xxx" to the <table> element rendered by WebGrid.GetHtml().
I tried to do this as follows:
grid.GetHtml(...
htmlAttributes: new { data_xxx = "value" }
);
However this renders as:
<table ... data_xxx="value">
instead of the expected:
<table ... data-xxx="value">
I.e. unlike other MVC helpers, it doesn't replace the underscore in the property name with a hyphen.
After a bit of spelunking with Reflector it seems that:
WebGrid.GetHtml() calls System.Web.WebPages.Html.ObjectToDictionary to convert the anonymous attributes object to a dictionary. Unlike the method System.Web.Mvc.HtmlHelper.AnonymousObjectToHtmlAttributes used by other helpers, this doesn't replace "_" by "-".
Unlike most other MVC helpers, WebGrid.GetHtml() does not have an overload that takes an IDictionary<string, object>, so I can't work around the bug by specifying the attributes in this way.
This looks like a bug to me, and I've submitted it to Connect:
http://connect.microsoft.com/VisualStudio/feedback/details/767456/webgrid-gethtml-helper-does-not-allow-data-attributes-to-be-set
Any suggestions for a workaround? Or is it fixed in MVC4?

Thanks for reporting this issue:
This was fixed yesterday in CodePlex by resolving issues 610 & 575.
https://aspnetwebstack.codeplex.com/workitem/610
https://aspnetwebstack.codeplex.com/workitem/575
You can try out the nightly bits.

Adding dashed property to HtmlHelper in MVC

I am using a Html.TextBoxFor helper in an MVC4 project. Our web designer used a custom property of "error-type" for his box that jquery/javascript looks at to determine how an error should be rendered for that textbox.
I tried doing something like:
#Html.TextBoxFor(m => m.SomeValue, new { error-type="blue" });
But C# doesn't like the property name of "error-type".
Is there a way to be able to use the custom property when rendering it through Razor?

Use an underscore; the helper will convert attribute names containing underscores to dashes. FYI, I believe this will only work with MVC-3 or later.
An alternate route is to use the overload that accepts an IDictionary<string, object> of HTML attributes. That will be both forwards and backwards compatible.
#Html.TextBoxFor(m => m.SomeValue, new Dictionary<string, object>{{"error-type", "blue"}})