What is the difference in these 2 underlying calls to create an instance?

Question

               Assembly assembly = Assembly.GetCallingAssembly();
               assembly.CreateInstance("MyType");

and

               Activator.CreateInstance(typeof(MyType));

Ok, the Activator.CreateInstance can be generic which eliminates the need to cast your created instance, but when would you use one against the other?

possible duplicate of [Difference between Assembly.CreateInstance and Activator.CreateInstance?](http://stackoverflow.com/questions/1833615/difference-between-assembly-createinstance-and-activator-createinstance) — annakata, Dec 03 '10 at 15:05

score 2 · Accepted Answer · answered Dec 03 '10 at 14:59

2

The string-based version looks only in the root namespace (since no namespace is included) of the current assembly (since no assembly name is included), plus a few system assemblies. The Type-based version already knows the type to use, so no search is necessary. It could be in any namespace or assembly, but the implication of typeof is that you could also have used "new".

The Type approach makes more sense when you will have a Type supplied at runtime, but not usually that close to the object creation.

answered Dec 03 '10 at 14:59

Marc Gravell

1,026,079
266
2,566
2,900

Great comment, we should marry our two comments and have little comment kids. We could name them Billy and Edwina. I know horrible name but my Grandfather's name was Billy so... – Dec 03 '10 at 15:03
does System in this case constitute the root: System System.Text? – dexter Dec 03 '10 at 20:04
@Max - yes; it would need to be the full namespace, for example System.Text.Regex ( although that lacks an empty ctor so would fail for unrelated reasons) – Marc Gravell Dec 03 '10 at 20:10

score 2 · Answer 2 · edited Feb 06 '11 at 01:59

2

In the first instance you could use that methodology to create an instance dynamically without knowing the type at run time. Where as the second one you need to know the type when you're writing the code.

edited Feb 06 '11 at 01:59

SLaks

868,454
176
1,908
1,964

answered Dec 03 '10 at 14:59

1

You could also use `Type.GetType(string typeName)` with Activator. – Matt Greer Dec 03 '10 at 15:01
Excellent point. Then you wouldn't be limited to the types in the existing assembly. – Dec 03 '10 at 15:23

score 2 · Answer 3 · answered Dec 03 '10 at 15:02

An obvious "problem" is that the former is stringly typed which is rarely a good thing, but it has the situational advantage of being runtime type checked so you have a level of dynamism. Personally, the refactor-factor outweighs dynamic design concerns mostly.

What is the difference in these 2 underlying calls to create an instance?

3 Answers3