What is the C# equivalent to Java's isInstance()?

Question

I know of is and as for instanceof, but what about the reflective isInstance() method?

Putrescible

Answer 1

The equivalent of Java’s obj.getClass().isInstance(otherObj) in C# is as follows:

bool result = obj.GetType().IsAssignableFrom(otherObj.GetType());

Note that while both Java and C# work on the runtime type object (Java java.lang.Class ≣ C# System.Type) of an obj (via .getClass() vs .getType()), Java’s isInstance takes an object as its argument, whereas C#’s IsAssignableFrom expects another System.Type object.

Brouwer

Note IsAssignableFrom takes a Type, not an object, so you need to actually do OtherObj.getType(). – Sulk

Thanks Jon – and remember, this is a wiki! I don't resent people correcting my mistakes. – Brouwer

interesting... in java, the JVM treats "instanceof" specially, apparently its very very fast, which may explain why its unusually a keyword (there is also an isAssignable method in java). – Nawab

Why is this method better then the "is" operator which is more readable? – Overbuild

@TimothyGonzalez Because it does something different. It tests whether two variables have the same type. is required a type name, by contrast. This is what OP wanted: the equivalent of Java's isInstance. The other answer is simply wrong despite the ridiculous number of upvotes. – Brouwer

Answer 2

bool result = (obj is MyClass); // Better than using 'as'

Crosswise

Does it work even for classes that use inheritance? (new Child() is Parent) – Eternalize

tested here, it works for classes that user inheritance. Thanks man. – Segovia

Answer 3

Depends, use is if you don't want to use the result of the cast and use as if you do. You hardly ever want to write:

if(foo is Bar) {
    return (Bar)foo;
}

Instead of:

var bar = foo as Bar;
if(bar != null) {
    return bar;
}

Terranceterrane

Answer 4

just off the top of my head, you could also do:

bool result = ((obj as MyClass) != null)

Not sure which would perform better. I'll leave it up to someone else to benchmark :)

Timberlake

Answer 5

Below code can be alternative to IsAssignableFrom.

parentObject.GetType().IsInstanceOfType(inheritedObject)

See Type.IsInstanceOfType description in MSDN.

Laurice