Asp.net-mvc – How much logic is allowed in ASP.NET MVC views

asp.net-mvcviews

In looking at samples of ASP.NET MVC sites, I'm seeing quite a bit of examples with embedded logic in the views, e.g.:

<% if (customerIsAllowed)
   { %>

   <p>nnn</p>
   <p>nnn</p>
   <p>nnn</p>
   <p>nnn</p>
   <p>nnn</p>

<% }  else {%>

   <p>nnn</p>
   <p>nnn</p>
   <p>nnn</p>
   <p>nnn</p>
   <p>nnn</p>

<% } %>

Although this seems wrong to me since it is the kind of thing we were trying to get away from in ASP 3.0, I have even heard in some podcasts how "a little bit of logic in view is ok" since the rest of the MVC framework is taking care of the structure that we didn't have in ASP 3.0.

Are there any MVC conventions specifying what kind and how much logic is allowed in views?

Best Answer

It depends on the reason for the logic. If the logic is choosing an alternate presentation based on some property passed to it by the controller, it is probably ok. This allows you some view reuse. Instead of having to recreate (and repeat) an entire view for each custom privilege, you can pass in some data that allows the view to be customized based on this privilege.

I think of this as a pragmatic balance between an idealized MVC and strict enforcement of DRY (don't repeat yourself). In some situations it is wiser to violate one or the other if you can't attain both easily. In the case where clearly the model and the basic view is the same, putting a little logic in the view to keep your views DRY is reasonable.

Related Solutions

Asp.net-mvc – Compile Views in ASP.NET MVC

From the readme word doc for RC1 (not indexed by google)

ASP.NET Compiler Post-Build Step

Currently, errors within a view file are not detected until run time. To let you detect these errors at compile time, ASP.NET MVC projects now include an MvcBuildViews property, which is disabled by default. To enable this property, open the project file and set the MvcBuildViews property to true, as shown in the following example:

<Project ToolsVersion="3.5" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <MvcBuildViews>true</MvcBuildViews>
  </PropertyGroup>

Note Enabling this feature adds some overhead to the build time.

You can update projects that were created with previous releases of MVC to include build-time validation of views by performing the following steps:

Open the project file in a text editor.
Add the following element under the top-most <PropertyGroup> element: <MvcBuildViews>true</MvcBuildViews>
At the end of the project file, uncomment the <Target Name="AfterBuild"> element and modify it to match the following:

<Target Name="AfterBuild" Condition="'$(MvcBuildViews)'=='true'">
    <AspNetCompiler VirtualPath="temp" PhysicalPath="$(ProjectDir)\..\$(ProjectName)" />
</Target>

C# – How to create a dropdownlist from an enum in ASP.NET MVC

For MVC v5.1 use Html.EnumDropDownListFor

@Html.EnumDropDownListFor(
    x => x.YourEnumField,
    "Select My Type", 
    new { @class = "form-control" })

For MVC v5 use EnumHelper

@Html.DropDownList("MyType", 
   EnumHelper.GetSelectList(typeof(MyType)) , 
   "Select My Type", 
   new { @class = "form-control" })

For MVC 5 and lower

I rolled Rune's answer into an extension method:

namespace MyApp.Common
{
    public static class MyExtensions{
        public static SelectList ToSelectList<TEnum>(this TEnum enumObj)
            where TEnum : struct, IComparable, IFormattable, IConvertible
        {
            var values = from TEnum e in Enum.GetValues(typeof(TEnum))
                select new { Id = e, Name = e.ToString() };
            return new SelectList(values, "Id", "Name", enumObj);
        }
    }
}

This allows you to write:

ViewData["taskStatus"] = task.Status.ToSelectList();

by using MyApp.Common