C# Static types cannot be used as parameters

Question

public static void SendEmail(String from, String To, String Subject, String HTML, String AttachmentPath = null, String AttachmentName = null, MediaTypeNames AttachmentType = null)
{
    ....

    // Add an attachment if required
    if (AttachmentPath != null)
    {
        var ct = new ContentType(MediaTypeNames.Text.Plain);
        using (var a = new Attachment(AttachmentPath, ct)
                    {
                        Name = AttachmentName,
                        NameEncoding = Encoding.UTF8,
                        TransferEncoding = TransferEncoding.Base64
                    })
        {
            mailMessage.Attachments.Add(a);
        }
    }

    ....
}

As you can see the MediaTypeNames AttachmentType throws the error:

'System.Net.Mime.MediaTypeNames': static types cannot be used as parameters

What is the best way to deal with this?

You are probably wanting to use "string" as the type. MediaTypeNames has a number of classes held within it each with some static properties that return strings. — PlayDeezGames
– PlayDeezGames, Commented Mar 7, 2012 at 2:53

user596075 · Accepted Answer · 2012-03-07 02:51:50Z

34

You can't pass a static type to a method as a parameter because then it would have to be instantiated, and you can't create an instance of a static class.

answered Mar 7, 2012 at 2:51

user596075

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3 Comments

Tom Gullen Over a year ago

This is what I figured, what would be a good way to solve this problem in my case?

user596075 Over a year ago

@TomGullen It's a static class, so you don't seem to need to instantiate it for your logic. You can just reference the class within your method. You don't need to pass it as a parameter, and you don't even reference the parameter name in your method. Just referencing the class name as static will be sufficient. You already do that correctly in your method. Long story short, just take out the parameter and you should be all set.

Daniel B Over a year ago

A class specified as a type parameter cannot be used for instantiatiation unless the type parameter has specified a "new" constraint. So it still doesn't make sense not to be able to pass a static type as parameter without the "new" constraint.

csblo · Accepted Answer · 2012-11-13 13:31:45Z

It's not recommended but you can simulate use of Static classes as parameters. Create an Instance class like this :

public class Instance
{

    public Type StaticObject { get; private set; }

    public Instance(Type staticType)
    {
        StaticObject = staticType;
    }

    public object Call(string name, params object[] parameters)
    {
        MethodInfo method = StaticObject.GetMethod(name);
        return method.Invoke(StaticObject, parameters);
    }

    public object Call(string name)
    {
        return Call(name, null);
    }

}

Then your function where you would use the static class :

    private static void YourFunction(Instance instance)
    {
        instance.Call("TheNameOfMethodToCall", null);
    }

For instance.Call :

The first parameter is the name of the method of your static class to call
The second parameter is the list of arguments to pass to the method.

And use like this :

    static void Main(string[] args)
    {

        YourFunction(new Instance(typeof(YourStaticClass)));

        Console.ReadKey();

    }

Primary Key · Accepted Answer · 2012-03-07 02:58:10Z

1

The best deal is definitely to remove the last parameter. Since type is static you don't need a reference to an instance and you can refer to its members from your function body.

edited Mar 7, 2012 at 2:58

answered Mar 7, 2012 at 2:51

Primary Key

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Comments

Pang · Accepted Answer · 2020-11-19 01:08:12Z

1

Use a different type for the argument.

A method argument needs to be of a type that can accept a reference to an instance, so it can't be a static class.

edited Nov 19, 2020 at 1:08

Pang

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answered Mar 7, 2012 at 2:52

Andrew Cooper

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Comments

Pang · Accepted Answer · 2020-11-19 01:08:55Z

1

You can wrap static types around an interface or another non-static class and add that as the parameter. Not ideal but a way around it. Or simply just reference the static type in the method body itself.

edited Nov 19, 2020 at 1:08

Pang

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answered Mar 7, 2012 at 2:51

aqwert

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Comments

Nikolai · Accepted Answer · 2014-07-25 02:45:16Z

0

Send a static class as the type of the parameter and then give it a variable name for use in the function. This works because the new variable is a reference to the static class. It is necessary to address the global variable problem. If you use a static class as a variable inside a method, you need to pass it in as a parameter, to avoid the global variable issue. This is basic structured programming 101 from the 80's.

answered Jul 25, 2014 at 2:45

Nikolai

11

1 Comment

Dave Cousineau Over a year ago

You can't pass a reference to a static class. You access the static members via the type name.

score 0 · Accepted Answer · 2015-06-01 16:05:05Z

0

It doesn't look like you even use that parameter in your method. You should just remove it because MediaTypeNames cannot be instantiated anyway.

edited Jun 1, 2015 at 16:05

answered Mar 7, 2012 at 4:59

user370770

Comments

Semir · Accepted Answer · 2021-02-02 00:31:36Z

0

A workaround to passing static parameters is to pass it as an object.

Function:

public static void HoldKey(object key)
{
   ...
}

Call function:

Function(static param);

answered Feb 2, 2021 at 0:31

Semir

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