C# – Rendering strongly-typed partial view with a different model

asp.netasp.net-mvc-3crazor

I have two views:
1) Register – primary view for creating user account
2) Category – partial view for adding category dynamically if it's not there in a register view combo field.

The Category view is shown as jQuery dialog when user click on Add Category while registering. This view shows fields required to make up a new category like name and description. For this reason, it has a separate model.

On get page everything works fine, however on post, if there's some validation error, the page needs to reload with user provider values for making correction, instead it throws following error:

Exception Details: System.InvalidOperationException: The model item passed into the dictionary is of type 'Delight.Models.User', but this dictionary requires a model item of type 'Delight.Models.Category'.

I thought that using the following statement might be causing this problem (since it doesn't specify the model object to use for partial view):

@Html.Partial("CreateCat")

However, resorting to the following overload didn't solve the problem either:

@Html.Partial("CreateCat", null, null)

Above the second parameter (with null value) represents the model object.

However, unexpectedly following solved my problem:

@Html.Partial("CreateCat", new Category(), null)

Why is empty object working in this case but null isn't?

Is there any other better way to render strongly-typed partial view with different model type.

Best Answer

Unless you want to use the parent's model or no model, you should always pass in the appropriate model for a partial view. Passing in null is silly, if you don't want an instantiated model in your partial view then why would your partial view use a model at all? In this instance, I think new Category() is the correct choice. However, I've always seen sub models passed into partials

@Html.Partial("CreateCat", Model.Category)

something about needing to do what you're doing seems strange, but I'm not certain how you're using the partial view.

Related Solutions

C# – String representation of an Enum

Try type-safe-enum pattern.

public sealed class AuthenticationMethod {

    private readonly String name;
    private readonly int value;

    public static readonly AuthenticationMethod FORMS = new AuthenticationMethod (1, "FORMS");
    public static readonly AuthenticationMethod WINDOWSAUTHENTICATION = new AuthenticationMethod (2, "WINDOWS");
    public static readonly AuthenticationMethod SINGLESIGNON = new AuthenticationMethod (3, "SSN");        

    private AuthenticationMethod(int value, String name){
        this.name = name;
        this.value = value;
    }

    public override String ToString(){
        return name;
    }

}

Update Explicit (or implicit) type conversion can be done by

adding static field with mapping
```
private static readonly Dictionary<string, AuthenticationMethod> instance = new Dictionary<string,AuthenticationMethod>();
```
- n.b. In order that the initialisation of the the "enum member" fields doesn't throw a NullReferenceException when calling the instance constructor, be sure to put the Dictionary field before the "enum member" fields in your class. This is because static field initialisers are called in declaration order, and before the static constructor, creating the weird and necessary but confusing situation that the instance constructor can be called before all static fields have been initialised, and before the static constructor is called.
filling this mapping in instance constructor
```
instance[name] = this;
```

and adding user-defined type conversion operator

public static explicit operator AuthenticationMethod(string str)
{
    AuthenticationMethod result;
    if (instance.TryGetValue(str, out result))
        return result;
    else
        throw new InvalidCastException();
}

C# – Case insensitive ‘Contains(string)’

You could use the String.IndexOf Method and pass StringComparison.OrdinalIgnoreCase as the type of search to use:

string title = "STRING";
bool contains = title.IndexOf("string", StringComparison.OrdinalIgnoreCase) >= 0;

Even better is defining a new extension method for string:

public static class StringExtensions
{
    public static bool Contains(this string source, string toCheck, StringComparison comp)
    {
        return source?.IndexOf(toCheck, comp) >= 0;
    }
}

Note, that null propagation ?. is available since C# 6.0 (VS 2015), for older versions use

if (source == null) return false;
return source.IndexOf(toCheck, comp) >= 0;

USAGE:

string title = "STRING";
bool contains = title.Contains("string", StringComparison.OrdinalIgnoreCase);

Best Answer

Related Solutions

C# – String representation of an Enum

C# – Case insensitive ‘Contains(string)’

Related Topic