Objective-C Runtime. Cocoa s Jewel in the Crown. NSConference Nicolas

Transcription

1 Objective-C Runtime Cocoa s Jewel in the Crown NSConference 2011 Nicolas

2 [isa kindof:magic]

3 1. Objective-C 2. Recipes 3. Introspection 4. Debugging

4 Objective-C Runtime OO, Smalltalk-like, dynamic extensions over C /usr/lib/libobjc.a.dylib /usr/include/objc/

5 Instances and Classes typedef struct objc_object { Class isa; } *id; typedef struct objc_class *Class; Class A (...) int i instance of B Class isa 0xA int i 0 NSString *s 0x0 BOOL NO Class B : A (...) superclass NSString *s BOOL b

6 Runtime Structure NSObject isa NSObject (meta) isa init alloc dealloc NSSet NSSet (meta) isa isa count set allobjects setwitharray: mymutableset NSMutableSet NSMutableSet (meta) Class isa 0xA isa isa addobject: setwithcapacity: removeobject:

7 Message Resolution bracket syntax is converted into objc_msgsend [myobject setvalue:3.0]; 3.0); objc_msgsend looksup the functions pointer IMP setvalue_ = class_getmethodimplementation( [myobject 3.0); it works thanks to meta-classes

8 [NSMutableSet set] NSObject isa NSObject (meta) isa init alloc dealloc NSSet NSSet (meta) isa isa count set allobjects setwitharray: NSMutableSet isa NSMutableSet (meta) isa addobject: setwithcapacity: removeobject:

9 [mymutableset count] NSObject isa NSObject (meta) isa init alloc dealloc NSSet NSSet (meta) isa isa count set allobjects setwitharray: mymutableset NSMutableSet NSMutableSet (meta) Class isa 0xA isa isa addobject: setwithcapacity: removeobject:

10 Runtime Benefits OO capabilities inheritance polymorphism Cocoa magic key-value coding plugins and frameworks UI with Interface Builder bigger underline bold responder chain database faulting undo manager

11 1. Objective-C 2. Recipes 3. Introspection 4. Debugging

12 Key-Value Coding -valueforkey: looks for methods, then ivars Person firstname { } firstname = John; lastname = Doe; [person setvaluesforkeyswithdictionary:d]; - (void)setvalue:(id)value forundefinedkey:(nsstring *)key { NSLog(@"-- unhandled key:%@", key); }

13 Categories A m1 m2 A m1 m2 A (A+Ext) - (id)m2 { /**/ } - (id)m3 { /**/

14 Method Swizzling m A 0xA [a m] -> 0xA() [a m2] -> 0xB() A+Ext m2 0xB // Google for Mike Ash implementation [a m] -> 0xB() [a m2] -> 0xA()

15 Logging NSURL Creation static IMP NSURL (Ext) + (void)swizzlemethods { // call this once, early original_initwithstring_ = method_getimplementation( class_getinstancemethod([self } // -[NSURL urlwithstring:] will now execute this method - (NSURL *)my_initwithstring:(nsstring *)s {! NSLog(@"-- my_initwithstring: %@", s);! return s);

16 High Order Functions $ python >>> l = ['a', 'bb', 'ccc'] >>> filter(lambda x:len(x) > 1, l) ['bb', 'ccc'] >>> map(lambda x:'-'+x, l) ['-a', '-bb', '-ccc'] >>> reduce(lambda x,y:x+y, l) 'abbccc'

17 Filtering NSArray NSArray *a = nil]; NSArray *b = [NSArray arraywithobjects:@"a", nil]; // 1. with plain C functions b = filter(a, startswitha); // 2. with NSInvocation b = [a nil]; // 3. with Objective-C blocks, since Mac OS X 10.6 and ios 4 b = [a filteredarrayusingpredicate:! [NSPredicate predicatewithblock:! ^BOOL(id s, NSDictionary *bindings) {!! return [s hasprefix:@"a"];! }]]); // 4. with high order messaging // b = [[a filter] hasprefix:@"a"];

18 High Order Messaging (1) [[a collect] uppercasestring]; [a ("a", "bb", "ccc") a proxy runtime collect uppercasestring forwardinvocation: collect: ("A", "BB", "CCC") ("A", "BB", "CCC")

19 High Order Messaging (2) Maybe one day we ll write Objective-C like this: users.collect.name users.do.logout users.sortedby.age users.any.is.admin users.all.are.admin

20 1. Objective-C 2. Recipes 3. Introspection 4. Debugging

21 Runtime Introspection // NSObject.h - (Class)class; - (id)performselector:(sel)aselector; - (BOOL)isKindOfClass:(Class)aClass; - (BOOL)respondsToSelector:(SEL)aSelector; // NSObjCRuntime.h NSClassFromString(@"NSArray"); NSStringFromClass([NSArray class]); NSSelectorFromString(@"objetAtIndex:"); NSStringFromSelector(@selector(objectAtIndex:)); // runtime.h Method class_getinstancemethod(class cls, SEL name); const char *ivar_gettypeencoding(ivar v); IMP method_getimplementation(method m); const char *property_getname(objc_property_t property);

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27 Runtime Browser Think class-dump, but dynamic! First version by Ezra Epstein, 2002 A development tool I found useful

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30 embedded web server

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32 Browsing the Runtime $ grep "hack" * -Ri // no, you are not alone... void *_odioushashhackstorage; BOOL _HACKpreviouslyHitPuck; BOOL _HACKpreviouslyHitKnob; BOOL _unused_ical_hack_[32]; -[NSWindow _evilhacktoclearlastlefthitinwindow]; -[UIDocumentInteractionController updatepopovercontentsizeforpresentationoftableviewhack]; -[PLStackView _validatetableviewlayerasahackforradar ];

33 Private APIs (un)safe on the App Store, blitz talk but as a dev you can write your own app anyway! // in UIStatusBarServerThread struct {! //...! NSInteger gsmsignalstrengthraw;! //...! NSUInteger datanetworktype;! //... } _statusbardata;

34 Mapping the Network

35 Scripting Cocoa $ python >>> from AppKit import NSSpeechSynthesizer >>> NSSpeechSynthesizer.availableVoices() ( "com.apple.speech.synthesis.voice.agnes", "com.apple.speech.synthesis.voice.albert", "com.apple.speech.synthesis.voice.alex",... )

36 1. Objective-C 2. Recipes 3. Introspection 4. Debugging

37 $ export OBJC_HELP=YES $ /Applications/TextEdit.app/Contents/MacOS/TextEdit (...) OBJC_HELP: describe available environment variables OBJC_PRINT_IMAGES: log image and library names as they are loaded OBJC_PRINT_LOAD_METHODS: log calls to class and category +load methods OBJC_PRINT_INITIALIZE_METHODS: log calls to class +initialize methods OBJC_PRINT_RESOLVED_METHODS: log methods created by +resolveclassmethod: and +resolveinstancemethod: (...)

38 $ export NSObjCMessageLoggingEnabled=YES $ /Applications/TextEdit.app/Contents/MacOS/TextEdit $ tail -f /tmp/msgsends-<pid> - NSLock NSLock lock + NSThread NSThread currentthread - NSThread NSObject hash - NSCFArray NSCFArray countbyenumeratingwithstate:objects:count: - NSLock NSLock unlock - NSLock NSLock lock + NSThread NSThread currentthread - NSThread NSObject hash - NSCFArray NSCFArray countbyenumeratingwithstate:objects:count: - NSLock NSLock unlock

39 DTrace $ cat objc_calls.d pid$target::*classdisplay*:entry {} pid$target::*classdisplay*:return {} $ sudo dtrace -s objc_calls.d -F -c./runtimebrowser dtrace: script 'objc_calls.d' matched 64 probes CPU FUNCTION 0 -> +[ClassDisplay classdisplaywithclass:] 0 -> -[ClassDisplay setrepresentedclass:] 0 <- -[ClassDisplay setrepresentedclass:] 0 <- +[ClassDisplay classdisplaywithclass:] 0 -> -[ClassDisplay setdisplaypropertiesdefaultvalues:] 0 <- -[ClassDisplay setdisplaypropertiesdefaultvalues:] 0 -> -[ClassDisplay header] 0 -> -[ClassDisplay setrefdclasses:] 0 <- -[ClassDisplay setrefdclasses:] (...)

40 gdb Cheat Sheet (gdb) break setpassword: (gdb) break -[Person setpassword:] (gdb) po self <Person: 0x10010c7a0> (gdb) po [invocation debugdescription] Some day, NSInvocation will have a useful debug (gdb) p (char *)_cmd $1 = 0x10fbb "setpassword:" (gdb) frame (gdb) info locals (gdb) info (classes selectors) [regex] (gdb) list +[Person string] (gdb) call [self setpassword:@"welcome"]

41 NSAutoreleasePool #include <Foundation/NSDebug.h> [NSAutoreleasePool showpools]; Autorelease Pools ==== top of stack ================ 0x583f3c0 ( NSDate) 0x583f350 (Measure) 0x5a24960 (UIWindow) (...) ==== top of pool, 23 objects ================ ==== top of pool, 0 objects ================ ==== top of pool, 0 objects ================

42 Useful Methods UIKit #ifdef DEBUG // strengthen your code [NSTimer scheduledtimerwithtimeinterval:1.0 target:application userinfo:nil repeats:yes]; #endif (gdb) po [UIView recursivedescription] <UIView: 0x4b4d3d0; frame = (0 20; ); (...) <MyView: 0x4b4b800; frame = (20 20; ); (...) <UIRoundedRectButton: 0x4b4e790; (...) <UIButtonLabel: 0x4b4f190; (...)

43 Conclusion Objective-C Runtime is not magic, it is just simple and clever Understanding Objective-C Runtime improves your code and debugging skills Objective-C is dynamic, it makes it powerful and fun!

44 [session release];