Objective-Hooker

Objective-Hooker is an extra tiny Objective-C framework that lets you hook Objective-C classes without using long and cumbersome syntax or an external preprocessor.

Features

• Simple to integrate – just add one header file and one source file to your project
• Simple to use – hooks are defined as if they were subclasses, use super to call the original implementation, or any other unhooked method
• Can hook classes with Swift-mangled names
• Lets you easily hook and use classes that you don't link against; useful for hooking classes that come from the main executable

How to use

For all uses, you first need to add ObjectiveHooker.h and ObjectiveHooker.m to your project.

Hooking a Class

Include ObjectiveHooker.h and the headers for the hooked class (In this example, AppKit.h for NSApplication). Use the OCHHookClass macro to declare a pair of a hooked class and a hooking class, followed by the hooking class's @implementation (Do not declare an @interface, OCHHookClass does that for you), which includes every instance or class method you want to hook. Use [super ...] to call unhooked methods from your implementations. For example:

#import <AppKit/AppKit.h>
#import "ObjectiveHooker.h"

OCHHookClass(NSApplication, NSApplicationHook)

@implementation NSApplicationHook
+ (instancetype) sharedApplication
{
    NSLog(@"OCHExampleHook");
    return [super sharedApplication];
}
@end

Note: Your hooking class must not declare any ivar, including implicit ivars auto-generated by properties.

Hooking and Using an Unlinked Class

To hook or use a class your library does link against (For example, when your library is injected into an executable, and you wish to use or hook some of its classes), first declare its @interface as you'd usually do, then use the OBHDynamicClass macro with the class name. This will allow you to use and hook that class as if you linked to it properly. For example:

@interface DOCKIndicatorLayer : CALayer
{
    @public
    int _currentIndicatorSize;
}

- (void)dockBackgroundChanged;
- (void)updateIndicatorForSize:(float)arg1;
@end

OBHDynamicClass(DOCKIndicatorLayer)

...

[[DOCKIndicatorLayer alloc] init]; // You can now use that class like any normal class

Hooking a Class with a Swift-Mangled name

To hook an Objective-C class that is implemented in Swift, and has a Swift-mangled name, use OBHHookSwiftClass instead of OCHHookClass. The OBHHookSwiftClass macro takes the Swift-mangled class name as the first argument, the hooking class name as the second argument, and the Objective-C non-mangled class name as the third argument. All Swift-mangled classes are treated as if they're dynamically linked using OBHDynamicClass, but will use the Objective-C name you used as the third argument (for example, in @interface or when calling class methods) for example:

@interface FloorLayer : CALayer
@end

OBHHookSwiftClass(Dock.FloorLayer, FloorLayerHook, FloorLayer)

@implementation FloorLayerHook
...
@end

License

Objective-Hooker is licensed under the MIT license, Copyright © 2018-2020 Lior Halphon