Aspect Oriented Programming 楊維中 a.k.a zonble [email protected] Thursday, September 12, 

zonble ฌᖯ؛ۇ Thursday, September 12, 

ᖯ৵ʔ݊ɓ˂ிϓٙ Unmaintainable 的 code 也是 Thursday, September 12, 

⼀一開始，程式邏輯就只有插 ⼊入資料⽽而已… - (void)appendData:(NSData *)inData { [_data appendData:inData]; } Thursday, September 12, 

後來，我們想確定傳⼊入的不 是 nil 或空資料 - (void)appendData:(NSData *)inData { NSParameterAssert(inData != nil); NSParameterAssert([inData length]); length = [_data length]; [_data appendData:inData]; NSAssert(length != [_data length]); } Thursday, September 12, 

後來，我們覺得 Release Build 也應該防⽌止輸⼊入空資料… - (void)appendData:(NSData *)inData { NSParameterAssert(inData != nil); NSParameterAssert([inData length]); if (!inData) { return; } if (![inData length]) { return; } length = [_data length]; [_data appendData:inData]; NSAssert(length != [_data length]); } Thursday, September 12, 

後來，我們發現這個 method 可能會在很多 thread 呼叫… - (void)appendData:(NSData *)inData { NSParameterAssert(inData != nil); NSParameterAssert([inData length]); if (!inData) { NSLog(@"inData is nil!"); return; } if (![inData length]) { NSLog(@"Length of inData is 0!"); return; } length = [_data length]; [_lock lock]; [_data appendData:inData]; [_lock unlock]; NSAssert(length != [_data length]); } Thursday, September 12, 

後來，在 Debug Build 裡頭要 加上 TestFlight CheckPoint - (void)appendData:(NSData *)inData { NSParameterAssert(inData != nil); NSParameterAssert([inData length]); if (!inData) { NSLog(@"inData is nil!"); return; } if (![inData length]) { NSLog(@"Length of inData is 0!"); return; } length = [_data length]; [_lock lock]; [_data appendData:inData]; [_lock unlock]; NSAssert(length != [_data length]); #if DEBUG [TestFlight passCheckpoint:@"APPEND_DATA"]; #endif } Thursday, September 12, 

Release Build 則要加上 Flurry Event Log… - (void)appendData:(NSData *)inData { NSParameterAssert(inData != nil); NSParameterAssert([inData length]); if (!inData) { NSLog(@"inData is nil!"); return; } if (![inData length]) { NSLog(@"Length of inData is 0!"); return; } length = [_data length]; [_lock lock]; [_data appendData:inData]; [_lock unlock]; NSAssert(length != [_data length]); #if DEBUG [TestFlight passCheckpoint:@"APPEND_DATA"]; #else [Flurry logEvent:@"APPEND_DATA"]; #endif } Thursday, September 12, 

還有 Google Analytics… - (void)appendData:(NSData *)inData { NSParameterAssert(inData != nil); NSParameterAssert([inData length]); if (!inData) { NSLog(@"inData is nil!"); return; } if (![inData length]) { NSLog(@"Length of inData is 0!"); return; } length = [_data length]; [_lock lock]; [_data appendData:inData]; [_lock unlock]; NSAssert(length != [_data length]); #if DEBUG [TestFlight passCheckpoint:@"APPEND_DATA"]; #else [Flurry logEvent:@"APPEND_DATA"]; idtracker = [[GAI sharedInstance] defaultTracker]; [tracker send: [[GAIDictionaryBuilder createEventWithCategory:@"data" withAction:@"append" withLabel:@"user_data" withValue:nil] build]]; #endif } Thursday, September 12, 

每件事情都很重要 • 確定傳⼊入參數的型態與內容 • 確定真的有插⼊入資料 • 加 Lock • 加 Debug Log • 加 TestFlight Log、Flurry Log… Thursday, September 12, 

23 ⾏行 code 中， ਂ͍ԫ̥ٙϞɓБf 這還不是最糟的… Thursday, September 12, 

更糟的是… 不只⼀一個 method 這樣 Thursday, September 12, 

ᒔึॎᕸ೻όٙࠠ͜ Thursday, September 12, 

上個世紀末，就有⼈人覺得… வᅵʔБ 接下來的故事請⾃自⼰己查 Wikipedia Thursday, September 12, 

AOP 的基本想法： Ҫ΢၇೷ౢආԸٙ
Code פᕎԨ܆ༀ ⽅方法很多 Thursday, September 12, 

Cross-cutting concerns …就是這些 • 確定傳⼊入參數的型態與內容 • 確定真的有插⼊入資料 • 加 Lock • 加 Debug Log • 加 TestFlight Log、Flurry Log… Thursday, September 12, 

Advice 

 

 在原本程式前後 插⼊入的程式碼 Thursday, September 12, 

Decorator Syntax …Objective C 不⽀支援 Thursday, September 12, 

Decorator Syntax def add(x): print "x:" + str(x) result = x + 1 print "result:" + str(result) return result Thursday, September 12, 

Decorator Syntax def log(func): def inner_func(*a): print "args:" + str(a) result = func(*a) print "result:" + str(result) return inner_func @log def add(x): return x + 1 Thursday, September 12, 

Objective-C 特性 Message Forwarding 當⼀一個物件不⽀支援某個 Selector 的時 候，這個物件可以決定把 Selector 交給 其他的物件。 Thursday, September 12, 

Message Forwarding - (void)forwardInvocation:(NSInvocation *)anInvocation { if ([someOtherObject respondsToSelector: [anInvocation selector]]) // Advice here [anInvocation invokeWithTarget:someOtherObject]; // Advice here else [super forwardInvocation:anInvocation]; } See: Objective-C Runtime Programming Guide Thursday, September 12, 

AOP-in-Objective-C https://github.com/moszi/AOP-in- Objective-C Thursday, September 12, 

Method Swizzling Thursday, September 12, 

Objective-C 第⼀一課 • ObjC 物件都是 C Structure • ObjC method 都是 C function pointer • 系統有⼀一個動態的索引表格，決定執⾏行 某個 selector 時，要對應到哪個 C function • Selector 就是索引表中的 key，型態為 C 字串 Thursday, September 12, 

Objective-C 第⼆二課 • ⼀一個 Class 有哪些 method，都是在 runtime 的時候建⽴立的 • 所以可以在 runtime 新增新的 method， 例如使⽤用 category 語法 • 也可以直接使⽤用 runtime API 把已經存在 的 method 換掉 Thursday, September 12, 

BOOL class_addMethod(Class cls, SEL name, IMP imp, const char *types); IMP method_setImplementation(Method method, IMP imp); Thursday, September 12, 

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AOP-for-Objective-C https://github.com/ndcube/AOP-for- Objective-C/ 在繼承關係的部份有些 bug，我⾃自⼰己有 先修，但是還沒有送 pull request… Thursday, September 12, 

Thank you! Thursday, September 12,