泛型类型的扩展方法

Question

How to create extension method for a generic type?

The below code returning error

Extension method can only be declared in non-generic, non-nested static class

Code:

public static class PagedList<T> where T : BaseEntity
{
    public static IEnumerable<T> ToPagedList(this IEnumerable<T> source, int pageNumber = 0, int pageSize = 5)
    {
        return source.Skip(pageNumber * pageSize).Take(pageSize);
    }
}

Any further implementation with this makes this work ?

Answer 1

Specify generic types directly on the method and make the class as the error says static and non-generic.

public static class PagedList
{
    public static IEnumerable<T> ToPagedList<T>(this IEnumerable<T> source, 
        int pageNumber = 0, int pageSize = 5) where T : BaseEntity
    {
        return source.Skip(pageNumber * pageSize).Take(pageSize);
    }
}

Answer 2

您应该收听错误消息，需要在非泛型类中声明扩展方法。