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?

score 191 · Answer 1 · answered Nov 12 '08 at 05:12

191

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

answered Nov 12 '08 at 05:12

Ana Betts

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Does it work even for classes that use inheritance? (`new Child() is Parent`) – Tomáš Zato Nov 03 '14 at 23:29
1

tested here, it works for classes that user inheritance. Thanks man. – Guilherme Golfetto Jan 04 '17 at 11:39

Konrad Rudolph · Accepted Answer · 2016-09-21T20:21:09.530

57

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.

edited Sep 21 '16 at 20:21

answered Nov 11 '08 at 23:13

Konrad Rudolph

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Note IsAssignableFrom takes a Type, not an object, so you need to actually do OtherObj.getType(). – FlySwat Nov 11 '08 at 23:25
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Thanks Jon – and remember, this is a wiki! I don't resent people correcting my mistakes. – Konrad Rudolph Nov 11 '08 at 23:34
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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). – Michael Neale Nov 11 '08 at 23:37
Why is this method better then the "is" operator which is more readable? – Timothy Gonzalez Sep 21 '16 at 15:01
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@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. – Konrad Rudolph Sep 21 '16 at 17:21

score 39 · Answer 3 · edited Jun 25 '14 at 14:11

39

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;
}

edited Jun 25 '14 at 14:11

Robert Gowland

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answered Nov 12 '08 at 05:30

score 2 · Answer 4 · edited Nov 12 '08 at 04:48

2

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 :)

edited Nov 12 '08 at 04:48

C. K. Young

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answered Nov 12 '08 at 01:10

CodingWithSpike

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score 2 · Answer 5 · answered Dec 28 '15 at 12:52

2

Below code can be alternative to IsAssignableFrom.

parentObject.GetType().IsInstanceOfType(inheritedObject)

See Type.IsInstanceOfType description in MSDN.

answered Dec 28 '15 at 12:52

Youngjae

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

5 Answers5

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