Цель доклада — вдохновить разработчиков на более глубокое изучение возможностей Objective-C Runtime, показать способы исследования системы, воодушевить аудиторию на эксперименты. В докладе показаны несколько примеров использования Objective-C Runtime для решения нетипичных задач. Первый пример - реализация простого KVO своими руками тремя способами. Вторым примером показана полезность исследования приватных классов. Рассказано, как во время работы программы получить информацию о протянутых IBOutlet и IBAction в xib и storyboard. В каждом примере присутствуют особенности реализации, на которых сделан акцент и показаны варианты решения или обхода.

1. Objective-C Runtime
Examples
https://github.com/storoj/objc_runtime_examples

2. Example 1.1
Observe value changes for all properties of a given class.

3. Class
Property
(objc_property_t)
getter
setter
Method
SEL
IMP

4. Sample class
@interface ELSample : NSObject
!
@property (nonatomic, strong) NSArray *values;
@property (nonatomic,
assign,
getter=isValid,
setter=setValidCustom:) BOOL valid;
!
@end
!
@implementation ELSample
!
@synthesize valid = ivar_valid;
!
@end

5. Class
Class sampleClass1 = [ELSample class];
Class sampleClass2 = NSClassFromString(@"ELSample");
#import <objc/runtime.h>
!
Class sampleClass3 = objc_getClass(“ELSample");
Class sampleClass4 = objc_lookUpClass(“ELSample");

6. Properties
unsigned int propertyCount = 0;
objc_property_t *properties = class_copyPropertyList(
sampleClass,
&propertyCount
);
!
for (unsigned int i=0; i<propertyCount; i++) {
objc_property_t property = properties[i];
!
const char *propertyName = property_getName(property);
NSLog(@"%s", propertyName);
}
free(properties);
Output:
values
valid

7. Property attributes
char const *attributesString = property_getAttributes(property);
NSLog(@"%s %s", propertyName, attributesString);
Output:
values T@"NSArray",&,N,V_values
valid Tc,N,GisValid,SsetValidCustom:,Vivar_valid
Code
Meaning
T
type (c - char, @ - id)
N
nonatomic
G
getter selector
S
setter selector
V
ivar name
&
strong/retain
More info

8. Property setter
/**
* @return The value string of the attribute attributeName if it exists in
* property, nil otherwise.
*/
!
char *property_copyAttributeValue(objc_property_t property,
const char *attributeName)
char *setterAttributeValue = property_copyAttributeValue(property, "S");
if (NULL == setterAttributeValue) {
"set" + capitalize(property_getName(property)) + ":"
}
// do not forget!
free(setterAttributeValue);

9. Method invocation
id objc_msgSend(id self, SEL _cmd, ...)
ELSample *sample = [ELSample new];
sample.valid = YES;
[sample setValidCustom:YES];
objc_msgSend(sample, @selector(setValidCustom:), YES);
id objc_msgSend(id self, SEL _cmd, ...)
{
IMP methodFunction = [[self class] methodForSelector:_cmd];
return methodFunction(self, _cmd, ...);
}

10. Method
Method *class_copyMethodList(Class cls, unsigned int *outCount)
!
Method class_getInstanceMethod(Class cls, SEL name)
!
Method class_getClassMethod(Class cls, SEL name)
IMP method_getImplementation(Method m)
!
/**
* @return The previous implementation of the method.
*/
IMP method_setImplementation(Method m, IMP imp)

11. Replacing method implementation
IMP method_setImplementation(Method m, IMP imp)
@interface Sample : NSObject
- (id)swizzleMe:(NSInteger)arg;
@end
Method method = class_getInstanceMethod(class, @selector(swizzleMe:));
typedef id (*IMP)(id, SEL, ...);
id SwizzleFunction(id self, SEL _cmd, NSInteger arg)
{
return @(arg+5);
}
!
method_setImplementation(method, (IMP)SwizzleFunction);

12. Blocks
id(^block)(id, id) = ^id(id self, id arg) {
NSLog(@"arg: %@", arg);
return nil;
};
IMP blockImp = imp_implementationWithBlock(block);
Block can capture original IMP to call it later.

13. NSString *setterName = property_getSetterName(property);
SEL setterSelector = NSSelectorFromString(setterName);
!
Method method = class_getInstanceMethod(class, setterSelector);
IMP originalImp = method_getImplementation(method);
!
id(^block)(id, ...) = ^id(id self, ...) {
NSLog(@"will change %s", property_getName(property));
return originalImp(self, setterSelector, ...);
};
!
IMP newImp = imp_implementationWithBlock(block);
!
method_setImplementation(method, newImp);
BUT…
return originalImp(self, setterSelector, ...);
(self, setterSelector, ...);
...
F*CK

14. Cast to concrete type
void(^block)(id, id) = ^void(id self, id arg) {
((void(*)(id, SEL, id))originalImp)(self, selector, arg);
};
// 0 - self, 1 - _cmd
char *argumentEncoding = method_copyArgumentType(method, 2);
id block = nil;
if (0 == strcmp(argumentEncoding, @encode(NSInteger))) {
block = ^void(id self, SEL selector, NSInteger arg) {
((void(*)(id, SEL, NSInteger))originalImp)(self, sel, arg);
};
} else if (...) {
...
}

15. Example 1.2

16. _objc_msgForward
id _objc_msgForward(id receiver, SEL sel, ...)
!
will call forwardInvocation: with prepared NSInvocation object
Method method = class_getInstanceMethod(class, setterSelector);
!
IMP originalImp = method_setImplementation(method, _objc_msgForward);
NSString *internalSetterName = [setterName
stringByAppendingString:@"_internal"];
SEL internalSelector = NSSelectorFromString(internalSetterName);
char const *types = method_getTypeEncoding(method);
class_addMethod(class, internalSelector, originalImp, types);
[capturedSelectorsSet addObject:setterName];

17. Replace forwardInvocation:
Method method = class_getInstanceMethod(class, @selector(forwardInvocation:));
IMP originalImp = method_getImplementation(method);
!
void(^block)(id, NSInvocation *) = ^void(id self, NSInvocation *invocation) {
NSString *selectorName = NSStringFromSelector([invocation selector]);
!
!
if ([capturedSelectorsSet containsObject:selectorName]) {
NSString *internalSelectorName = [selectorName
stringByAppendingString:@“_internal"];
[invocation setSelector:NSSelectorFromString(internalSelectorName)];
[invocation invoke];
} else {
((void(*)(id, SEL, NSInvocation *)) originalImp)(self,
@selector(forwardInvocation:),
invocation);
}
};
!
method_setImplementation(method, imp_implementationWithBlock(block));

18. Example 1.3

19. Replace the class
Class object_setClass(id obj, Class cls)
NSNumber *number = [NSNumber numberWithDouble:5.1f];
!
Class class = [number class];
NSLog(@"number: %@ %@ %p", number, class, (__bridge void *)number);
// number: 5.099999904632568 __NSCFNumber 0x8d464c0
!
object_setClass(number, [NSObject class]);
NSLog(@"number: %@", number);
// number: <NSObject: 0x8d464c0>
object_setClass(number, class);
NSLog(@"number: %@", number);
// number: 5.099999904632568

20. NSProxy
“… Subclasses of NSProxy can be used to
implement transparent distributed messaging…”
Some people, when confronted with a
problem, think "I know, I'll use NSProxy." Now
they have two problems.

21. @interface Observer : NSProxy
+ (instancetype)observerWithObject:(id)object;
@end
!
@implementation Observer
!
- (void)forwardInvocation:(NSInvocation *)anInvocation
{
Class realClass = objc_getAssociatedObject(self, "realClass");
SEL selector = [anInvocation selector];
objc_property_t property = class_getPropertyWithSetter(realClass, selector);
if (NULL != property) {
NSLog(@"changing %s", property_getName(property));
}
!
}
Class currentClass = [self class];
object_setClass(self, realClass);
[anInvocation invoke];
object_setClass(self, currentClass);
!
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel
{
Class realClass = objc_getAssociatedObject(self, "realClass");
NSMethodSignature *sig = [realClass instanceMethodSignatureForSelector:sel];
return signature;
}
!
@end

22. Example 2
Get outlets and actions runtime

23. UIRuntimeConnection
UIRuntimeOutletConnection
UIRuntimeEventConnection
UIRuntimeOutletCollectionConnection

24. @interface UIRuntimeConnection : NSObject <NSCoding>
!
@property (nonatomic, strong) id destination;
@property (nonatomic, strong) NSString *label;
@property (nonatomic, strong) id source;
!
- (void)connect;
- (void)connectForSimulator;
!
@end
!
@interface UIRuntimeEventConnection : UIRuntimeConnection
!
@property (nonatomic, readonly) SEL action;
@property (nonatomic, assign) UIControlEvents eventMask;
@property (nonatomic, readonly) id target;
!
@end
!
@interface UIRuntimeOutletConnection : UIRuntimeConnection
@end

25. kennytm
https://github.com/kennytm/iphone-private-frameworks
class-dump-z
https://code.google.com/p/networkpx/wiki/class_dump_z
runtime
Class *objc_copyClassList(unsigned int *outCount)
Protocol * __unsafe_unretained *objc_copyProtocolList(unsigned int *outCount)
Ivar *class_copyIvarList(Class cls, unsigned int *outCount)
Method *class_copyMethodList(Class cls, unsigned int *outCount)
Protocol * __unsafe_unretained *class_copyProtocolList(Class cls,
unsigned int *outCount)
objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)

26. SEL selector = NSSelectorFromString(@"initWithCoder:");
!
Class outletClass = NSClassFromString(@"UIRuntimeOutletConnection");
Method outletMethod = class_getInstanceMethod(outletClass, selector);
method_swizzle(outletMethod, ...);
!
Class eventClass = NSClassFromString(@"UIRuntimeEventConnection");
Method eventMethod = class_getInstanceMethod(eventClass, selector);
method_swizzle(eventMethod, ...)
NO!
Why not?.. Looks good.

27. SEL selector = NSSelectorFromString(@"initWithCoder:");
!
Class outletClass = NSClassFromString(@"UIRuntimeOutletConnection");
Method outletMethod = class_getInstanceMethod(outletClass, selector);
!
Class eventClass = NSClassFromString(@"UIRuntimeEventConnection");
Method eventMethod = class_getInstanceMethod(eventClass, selector);
!
Class baseClass = NSClassFromString(@"UIRuntimeConnection");
Method baseMethod = class_getInstanceMethod(baseClass, selector);
!
baseMethod == outletMethod
baseMethod != eventMethod
@implementation UIRuntimeEventConnection
!
- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super initWithCoder:aDecoder];
if (self) {
// decode eventMask
}
return self;
}
!
@end

28. Copy method before swizzling
SEL selector = NSSelectorFromString(@"initWithCoder:");
!
Class baseClass = NSClassFromString(@"UIRuntimeConnection");
Method baseMethod = class_getInstanceMethod(baseClass, selector);
!
Class outletClass = NSClassFromString(@"UIRuntimeOutletConnection");
class_addMethod(outletClass, selector,
method_getImplementation(baseMethod),
method_getTypeEncoding(baseMethod));
!
Method outletMethod = class_getInstanceMethod(outletClass, selector);
!
method_swizzle(outletMethod, ...);

29. Be a man!
SEL selector = NSSelectorFromString(@"initWithCoder:");
!
Class baseClass = NSClassFromString(@"UIRuntimeConnection");
Method baseMethod = class_getInstanceMethod(baseClass, selector);
!
Class outletClass = NSClassFromString(@"UIRuntimeOutletConnection");
!
id(^initWithCoderBlock)(id, id) = ^id(id aSelf, id aDecoder) {
struct objc_super _super = {
.receiver = aSelf,
.super_class = [[aSelf class] superclass]
};
!
return objc_msgSendSuper(&_super, selector, aDecoder);
};
IMP initWithCoderImp = imp_implementationWithBlock(initWithCoderBlock);
!
class_addMethod(outletClass, selector, initWithCoderImp,
method_getTypeEncoding(baseMethod));

30. Output
UIStoryboardScene got ELViewController *sceneViewController
ELViewController got UIStoryboard *storyboard
UIControlEventTouchUpInside -[ELViewController buttonTap:(UIButton *)]
UIControlEventEditingChanged -[ELViewController
datePickerEditingChanged:(UIDatePicker *)]
UITableView got ELViewController *dataSource
ELViewController got UIDatePicker *datePicker
UITableView got ELViewController *delegate
ELViewController got UILabel *label
ELViewController got UIView *view

31. Useful links
•
•
•
•
•
•
•
Property introspection
imp_implementationWithBlock
class loading and initialization
let's build objc_msgSend
objc_msgSend ARM assembly
private frameworks
Objective-C Runtime Programming Guide