通过类型作为参数并检查

Question

I want to build a method that accepts parameter as Type like

void M1(Type t)
{
  // check which type it is
}

and call it like

M1(typeof(int));

I have no idea how to check type in method body.

I have tried

if (t is double)

But it is giving warning

The given expression never provided type (double)

Please help me for checking the type of parameter.

Answer 1

If you want to check for an exact type, you can use:

if (t == typeof(double))

That's fine for double , given that it's a struct, so can't be inherited from.

If you want to perform a more is-like check - eg to check whether a type is compatible with System.IO.Stream - you can use Type.IsAssignableFrom :

if (typeof(Stream).IsAssignableFrom(t))

That will match if t is System.IO.MemoryStream , for example (or if it's System.IO.Stream itself).

I always find myself having to think slightly carefully to work out which way round the call goes, but the target of the call is usually a typeof expression.

Answer 2

You can try

  if(t == typeof(double))

or

 if (typeof(double).IsAssignableFrom(t))

or

 if(t == default(double).GetType())

or

 if(t.Name == "Double")

Personally i prefer the first option

Answer 3

Have a look at IsAssignableFrom , which determines whether an instance of a specified type can be assigned to the current type instance.

public void M<T>(T value) 
{
    if (typeof(T).IsAssignableFrom(typeof(double)))
        Console.Write("It's a double");  
}

It returns true if the given parameter:

• represents the same type.

• is derived either directly or indirectly from the current instance.

• is a generic type parameter, and the current instance represents one of the constraints of the parameter.

• represents a value type, and the current instance represents Nullable (Nullable(Of paramerter) in Visual Basic).