© 2013 Jonas Gessner

An easy to use Objective-C level API for swizzling class and instance methods, as well as swizzling instance methods on specific instances only.

Documentation

For further examples see the JGMethodSwizzlerTests Xcode project.

JGMethodSwizzler can be used for three basic swizzling types: Swizzling a specific method for all instances of a class, swizzling class methods and swizzling instance methods of specific instances only.

JGMethodSwizzler is completely thread safe and can handle multiple swizzles. Instance-specific swizzling should however not be combined with global swizzling in the same method.

Swizzling a class method:

Swizzling the method +(int)[TestClass test:(int)]

[TestClass swizzleClassMethod:@selector(test:) withReplacement:JGMethodReplacementProviderBlock {
    //return a replacement block
    return JGMethodReplacement(int, const Class *, int arg) {
        //get the original value
        int orig = JGOriginalImplementation(int, arg);
        //return the modified value
        return orig+2;
    };
}];

After this code is run, calling the method will return the modified value until the method is deswizzled.

Swizzling an instance method across all instances of a class:

Swizzling the method -(int)[TestClass test:(int)]

[TestClass swizzleInstanceMethod:@selector(test:) withReplacement:JGMethodReplacementProviderBlock {
    //return a replacement block
    return JGMethodReplacement(int, TestClass *, int arg) {
        //get the original value
        int orig = JGOriginalImplementation(int, arg);
        //return the modified value
        return orig+2;
    };
}];

After this code is run, calling the method will return the modified value until the method is deswizzled.

Swizzling an instance method for a specific instance:

Swizzling the description method on a specific NSObjectinstance:

NSObject *object = [NSObject new];

[object swizzleMethod:@selector(description) withReplacement:JGMethodReplacementProviderBlock {
    return JGMethodReplacement(NSString *, NSObject *) {
        NSString *orig = JGOriginalImplementation(NSString *);

        return [orig stringByAppendingString:@" Swizzled!!"];
    };
}];

After this code is run, calling the method will return the modified value until the method is deswizzled.

Deswizzling

All swizzles can be removed once they've been applied.

deswizzleAll() removes all swizzles.

Deswizzling global class and instance swizzles

deswizzleGlobal() removes all swizzles that have been applied as global swizzles (not instance specific).

+deswizzleClassMethod:(SEL) deswizzles a specific class method.

+deswizzleInstanceMethod:(SEL) deswizzles a specific instance method.

+deswizzleAllClassMethods deswizzles all swizzled class methods of this class.

+deswizzleAllInstanceMethods deswizzles all swizzled instance methods of this class.

+deswizzleAllMethods deswizzles all swizzled methods of this class.

Deswizzling Instance specific swizzles

deswizzleInstances() removes all swizzles that have been applied as instance specific swizzles.

-deswizzleMethod:(SEL) deswizzles a specific instance method of this instance.

-deswizzle deswizzles all swizzled instance methods of this instance.

Notes

JGMethodSwizzler works with both ARC and MRC/MRR.

Credits

Created by Jonas Gessner.

Thanks to Andrew Richardson for his inspiration and contribution with InstanceHook.

License

Licensed under the MIT license.