C# 静态类型不能用作参数

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?

Answer 1

您不能将静态类型作为参数传递给方法，因为这样就必须对其进行实例化，并且您无法创建static类的实例。

Answer 2

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();

    }

Answer 3

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.

Answer 4

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.

Answer 5

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.

Answer 6

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.

Answer 7

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);

Answer 8

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