转换：从对象类型检索的System.Attribute

Question

I've written (using a sneak peek on the net) my generic method to get attributes on classnames. Here is the code.

The attribute:

[System.AttributeUsage(System.AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
public class FileType : Attribute
{
    public String TypeName { get; set; }
}

The implementation

[FileType (TypeName ="wordFile")]
public class BudFile
{ ... }

My Generic Method

    public T GetAttributeOfObject<T>(Type objectTypeToCheck)
    {
        object myAttribute = (T)Attribute.GetCustomAttribute(objectTypeToCheck, typeof(T));
    }

The Usage:

BudFile A;
FileType myFileType = GetAttributeOfObject<FileType>(typeof(A));

The Problem:

I'm getting the error Cannot convert type System.Attribute to T on the following line:

        object myAttribute = (T)Attribute.GetCustomAttribute(objectTypeToCheck, typeof(T));

Which makes sense since Attribute.GetCustomAttribute returns an object of System.Attribute . How can I Safely cast the retrieved System.Attribute to my attribute?

Answer 1

You simply need a constraint for T as Attribute . You get the compiler error because T could be anything which can't be casted to an Attribute type.

public T GetAttributeOfObject<T>(Type objectTypeToCheck) where T: Attribute
{
    return (T)Attribute.GetCustomAttribute(objectTypeToCheck, typeof(T));
}