Objective C : Given a Class id, can I check if this class implements a certain protocol? Or has a certain selector?
21,415
Solution 1
Class klass = NSClassFromString(classname);
if ([klass instancesRespondToSelector:@selector(create)]) {
[[klass alloc] create];
}
May I, however, point out just how many awful Objective-C rules you're breaking by doing the above? For example, you should never be calling methods on an allocated-but-not-initialized instance. The Xcode Static Analyzer will give you all sorts of warnings about memory leaks.
A better option would be this:
[[[klass alloc] init] create];
But you seem to imply that you don't want to call init.
You could consider a class method: [klass create]
, which would return a non-owned instance of klass
. Then you'd just check [klass respondsToSelector:@selector(create)]
before calling it.
Solution 2
NSString *className; //assume this exists
Class class = NSClassFromString(className);
if ([class conformsToProtocol:@protocol(SomeProtocol)]) {
id instance = [[class alloc] init];
[instance create];
}
Author by
Jacko
Updated on February 28, 2020Comments
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Jacko over 4 years
I want to use this for an object factory: Given a string, create a Class, and if this Class supports a protocol (with a Create() method) then alloc the class and call Create.
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Jacko over 14 yearsThanks. You're right, the Create method should be a class method. I think this is usually how object factories are designed.
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ctpenrose almost 11 yearsHe asked two questions in his title :)
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keeshux almost 10 yearsOne step further:
id<SomeProtocol> instance = [[class alloc] init]
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paiego almost 10 yearsIf you don't have or know the class name, then use [instance class] or NSStringFromClass([instance class])
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rafaperez over 9 yearsThis is not the best answer. Chuck is better.