MVC Razor: Helper method to render alternate content when empty - asp.net-mvc

Question

I've got some data, and sometimes that data is blank. Instead of making a bunch of crazy logic on my view I'd rather use a helper method that will render the data if it exists, and render some HTML that just says "N/A" when the string is empty/null.
Ideal syntax: #Helpers.RenderThisOrThat(Model.CustomerPhone)
If the Model.CustomerPhone (a string) is empty it will render this alternate HTML instead: <span class='muted'>N/A</span>
Here's what we have so far:
#helper RenderThisOrThat(string stringToRender, string methodToGetAlternateText = null)
{
#RenderThisOrThat(MvcHtmlString.Create(stringToRender), methodToGetAlternateText)
}
#helper RenderThisOrThat(MvcHtmlString stringToRender, string methodToGetAlternateText = null)
{
if (string.IsNullOrWhiteSpace(stringToRender.ToHtmlString()))
{
if (!string.IsNullOrWhiteSpace(methodToGetAlternateText)) {
#methodToGetAlternateText
}
<span class='muted'>N/A</span>
}
#stringToRender
}
This works just fine until we want to pass something other than a string into either parameter. For example when we have an email address we want it to be a link to that email and not just the string of the email.
#Helpers.RenderThisOrThat(##Html.DisplayFor(m => m.CustomerEmail))
It gives us the error: "Cannot convert lambda expression to type 'string' because it is not a delegate type"
We are at a loss for how to make this work... any help here?

Answer 1

You're looking for a helpers that will take a string and:
If the string is not empty, render that string.
If the string is not empty, render a given template.
If the string is empty, render "N/A" html.
If the string is empty, render a given template.
When passing a razor block to a function as a parameter, razor packages the block as Func. Change the parameters in the helper functions to take that type of delegate and don't forget to call those delegates (I chose to pass null).
These helpers should handle those scenarios.
Solution
#helper RenderThisOrThat(string stringToRender, Func<object, IHtmlString> leftTemplate = null, Func<object, IHtmlString> rightTemplate = null)
{
var shouldRenderLeft = !string.IsNullOrWhiteSpace(stringToRender);
leftTemplate = leftTemplate ?? (o => MvcHtmlString.Create(stringToRender));
#RenderThisOrThat(shouldRenderLeft, leftTemplate, rightTemplate)
}
#helper RenderThisOrThat(bool shouldRenderLeft, Func<object, IHtmlString> leftTemplate, Func<object, IHtmlString> rightTemplate = null)
{
var shouldRenderRight = !shouldRenderLeft;
if (shouldRenderRight)
{
if (rightTemplate != null)
{
#rightTemplate(null)
}
else
{
<span class='muted'>N/A</span>
}
}
else
{
#leftTemplate(null)
}
}
Examples
1. #Helpers.RenderThisOrThat(Model.StringWithBob)
2. #Helpers.RenderThisOrThat(Model.StringWithNull)
3. #Helpers.RenderThisOrThat(Model.StringWithBob, #<span>I'm #Model.StringWithBob</span>)
4. #Helpers.RenderThisOrThat(Model.StringWithNull, #<span>I'm #Model.StringWithBob</span>)
5. #Helpers.RenderThisOrThat(Model.StringWithBob, #<span>I'm #Model.StringWithBob</span>, #<span>What about Bob?</span>)
6. #Helpers.RenderThisOrThat(Model.StringWithNull, #<span>I'm #Model.StringWithBob</span>, #<span>What about Bob?</span>)
Will output:
Bob
<span class='muted'>N/A</span>
<span>I'm Bob</span>
<span class='muted'>N/A</span>
<span>I'm Bob</span>
<span>What about Bob?</span>

Answer 2

This is an awfully complex solution to a simple problem. You don't need to create complex views, in fact, you should be using an Editor/DisplayTemplate, then you put your logic in the template and it's done once, without all the need for extra inclusion of helper functions, or anything else.
You can also go a step further here, because in this case you're rendering an email address. You apply a DataType attribute to your model and then specify an Phone Number rendering type.
public class MyModel {
[DataType(DataType.PhoneNumber)]
public string PhoneNumber {get;set;}
}
Then you create a folder in ~/Views/Shared called DisplayTemplates and in that folder create a file called PhoneNumber.cshtml, in it you do this:
#model string
#if (string.IsEmptyOrWhiteSpace(Model)) {
#:<span class='muted'>N/A</span>
} else {
#: <span>#Model</span>
}
Then, in your view:
#Html.DisplayFor(x => x.PhoneNumber)
That's it, no complex logic in your view, no convluted helper functions everywhere. This is simple, easy, and maintainable. You can do the same for Email address as there is an EmailAddress datatype as well.
MVC has a lot of very good functionality built-in that most people simply do not use, because they haven't spent any real time learning it.