Objc Runtime在專案中該怎麼用
從以下四個方面講述Objc Runtime在專案中的使用場景，使用的例子來自於github上的開源專案FDFullscreenPopGesture、GVUserDefaults 以及系統中KVO的底層實現例子
- Method Swizzling
- 動態方法新增
- isa Swizzling
- 訊息轉發
Method Swizzling
Method Swizzling簡單的講就是方法替換，是一種hook技術，一個典型的Method Swizzling例子如下，註釋部分說明了為什麼這麼做。
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
Class class = [self class];
// When swizzling a class method, use the following:
// Class class = object_getClass((id)self);
SEL originalSelector = @selector(viewWillAppear:);
SEL swizzledSelector = @selector(xxx_viewWillAppear:);
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
// 在進行Swizzling的時候，我們需要用class_addMethod先進行判斷一下原有類中是否有要替換的方法的實現。
BOOL didAddMethod = class_addMethod(class,
originalSelector,
method_getImplementation(swizzledMethod),
method_getTypeEncoding(swizzledMethod));
if (didAddMethod) {
// 如果class_addMethod返回YES，說明當前類中沒有要替換方法的實現，我們需要在父類中去尋找。這個時候就需要用到method_getImplementation去獲取class_getInstanceMethod裡面的方法實現。然後再進行class_replaceMethod來實現Swizzling。
class_replaceMethod(class,
swizzledSelector,
method_getImplementation(originalMethod),
method_getTypeEncoding(originalMethod));
} else {
// 如果class_addMethod返回NO，說明當前類中有要替換方法的實現，所以可以直接進行替換，呼叫method_exchangeImplementations即可實現Swizzling。
method_exchangeImplementations(originalMethod, swizzledMethod);
}
});
}
#pragma mark - Method Swizzling
- (void)xxx_viewWillAppear:(BOOL)animated {
// 由於我們進行了Swizzling，所以其實在原來的- (void)viewWillAppear:(BOOL)animated方法中，呼叫的是- (void)xxx_viewWillAppear:(BOOL)animated方法的實現。所以不會造成死迴圈。相反的，如果這裡把[self xxx_viewWillAppear:animated];改成[self viewWillAppear:animated];就會造成死迴圈。因為外面呼叫[self viewWillAppear:animated];的時候，會交換方法走到[self xxx_viewWillAppear:animated];這個方法實現中來，然後這裡又去呼叫[self viewWillAppear:animated]，就會造成死迴圈了。
[self xxx_viewWillAppear:animated];
NSLog(@"viewWillAppear: %@", self);
}
複製程式碼FDFullscreenPopGesture 這個庫使用的就是Method Swizzling技術實現的全屏手勢返回的效果
UINavigationController (FDFullscreenPopGesture)分類的load方法中替換了系統的pushViewController:animated:方法
+ (void)load
{
// Inject "-pushViewController:animated:"
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
Class class = [self class];
SEL originalSelector = @selector(pushViewController:animated:);
SEL swizzledSelector = @selector(fd_pushViewController:animated:);
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
BOOL success = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
if (success) {
class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, swizzledMethod);
}
});
}
複製程式碼在替換的方法中禁用了系統的邊緣返回手勢，新增了自定義的手勢來處理
- (void)fd_pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
if (![self.interactivePopGestureRecognizer.view.gestureRecognizers containsObject:self.fd_fullscreenPopGestureRecognizer]) {
// Add our own gesture recognizer to where the onboard screen edge pan gesture recognizer is attached to.
[self.interactivePopGestureRecognizer.view addGestureRecognizer:self.fd_fullscreenPopGestureRecognizer];
// Forward the gesture events to the private handler of the onboard gesture recognizer.
NSArray *internalTargets = [self.interactivePopGestureRecognizer valueForKey:@"targets"];
id internalTarget = [internalTargets.firstObject valueForKey:@"target"];
SEL internalAction = NSSelectorFromString(@"handleNavigationTransition:");
self.fd_fullscreenPopGestureRecognizer.delegate = self.fd_popGestureRecognizerDelegate;
[self.fd_fullscreenPopGestureRecognizer addTarget:internalTarget action:internalAction];
// Disable the onboard gesture recognizer.
self.interactivePopGestureRecognizer.enabled = NO;
}
// Handle perferred navigation bar appearance.
[self fd_setupViewControllerBasedNavigationBarAppearanceIfNeeded:viewController];
// Forward to primary implementation.
if (![self.viewControllers containsObject:viewController]) {
[self fd_pushViewController:viewController animated:animated];
}
}
複製程式碼然後在自定義的手勢的回撥方法gestureRecognizerShouldBegin中處理手勢的返回
- (BOOL)gestureRecognizerShouldBegin:(UIPanGestureRecognizer *)gestureRecognizer
{
// Ignore when no view controller is pushed into the navigation stack.
if (self.navigationController.viewControllers.count <= 1) {
return NO;
}
// Ignore when the active view controller doesn't allow interactive pop.
UIViewController *topViewController = self.navigationController.viewControllers.lastObject;
if (topViewController.fd_interactivePopDisabled) {
return NO;
}
// Ignore when the beginning location is beyond max allowed initial distance to left edge.
CGPoint beginningLocation = [gestureRecognizer locationInView:gestureRecognizer.view];
CGFloat maxAllowedInitialDistance = topViewController.fd_interactivePopMaxAllowedInitialDistanceToLeftEdge;
if (maxAllowedInitialDistance > 0 && beginningLocation.x > maxAllowedInitialDistance) {
return NO;
}
// Ignore pan gesture when the navigation controller is currently in transition.
if ([[self.navigationController valueForKey:@"_isTransitioning"] boolValue]) {
return NO;
}
// Prevent calling the handler when the gesture begins in an opposite direction.
CGPoint translation = [gestureRecognizer translationInView:gestureRecognizer.view];
BOOL isLeftToRight = [UIApplication sharedApplication].userInterfaceLayoutDirection == UIUserInterfaceLayoutDirectionLeftToRight;
CGFloat multiplier = isLeftToRight ? 1 : - 1;
if ((translation.x * multiplier) <= 0) {
return NO;
}
return YES;
}
複製程式碼動態方法新增
GVUserDefaults 是一個屬性和NSUserDefaults之間實現自動寫入和讀取的開源庫，該庫（當前最新版本 1.0.2）使用到的技術就是動態方法新增，專案中使用到的主要技術點列舉如下：
class_copyPropertyList獲取類的property列表property_getName獲取property名稱property_getAttributes獲取property的屬性，可以參考Property Attribute Description Examplessel_registerName註冊SELclass_addMethod新增方法
主要看generateAccessorMethods方法的實現，該方法自動生成屬性對應的Getter和Setter方法，關鍵的地方有新增了註釋
- (void)generateAccessorMethods {
unsigned int count = 0;
// 獲取類的屬性列表
objc_property_t *properties = class_copyPropertyList([self class], &count);
self.mapping = [NSMutableDictionary dictionary];
for (int i = 0; i < count; ++i) {
objc_property_t property = properties[i];
// 獲取property名稱
const char *name = property_getName(property);
// 獲取property的屬性
const char *attributes = property_getAttributes(property);
char *getter = strstr(attributes, ",G");
if (getter) {
// getter修飾的屬性：@property (nonatomic, getter=zytCustomerGetter) float customerGetter; -> "Tf,N,GzytCustomerGetter"
getter = strdup(getter + 2);
getter = strsep(&getter, ",");
} else {
getter = strdup(name);
}
SEL getterSel = sel_registerName(getter);
free(getter);
char *setter = strstr(attributes, ",S");
if (setter) {
// setter 修飾的屬性：@property (nonatomic, setter=zytCustomerSetter:) float customerSetter; -> Tf,N,SzytCustomerSetter:
setter = strdup(setter + 2);
setter = strsep(&setter, ",");
} else {
asprintf(&setter, "set%c%s:", toupper(name[0]), name + 1);
}
// 註冊SEL
SEL setterSel = sel_registerName(setter);
free(setter);
// 同一個屬性的`Getter`或者`Setter`方法在`self.mapping`對應的值是一樣的，
NSString *key = [self defaultsKeyForPropertyNamed:name];
[self.mapping setValue:key forKey:NSStringFromSelector(getterSel)];
[self.mapping setValue:key forKey:NSStringFromSelector(setterSel)];
IMP getterImp = NULL;
IMP setterImp = NULL;
char type = attributes[1];
switch (type) {
case Short:
case Long:
case LongLong:
case UnsignedChar:
case UnsignedShort:
case UnsignedInt:
case UnsignedLong:
case UnsignedLongLong:
getterImp = (IMP)longLongGetter;
setterImp = (IMP)longLongSetter;
break;
case Bool:
case Char:
getterImp = (IMP)boolGetter;
setterImp = (IMP)boolSetter;
break;
case Int:
getterImp = (IMP)integerGetter;
setterImp = (IMP)integerSetter;
break;
case Float:
getterImp = (IMP)floatGetter;
setterImp = (IMP)floatSetter;
break;
case Double:
getterImp = (IMP)doubleGetter;
setterImp = (IMP)doubleSetter;
break;
case Object:
getterImp = (IMP)objectGetter;
setterImp = (IMP)objectSetter;
break;
default:
free(properties);
[NSException raise:NSInternalInconsistencyException format:@"Unsupported type of property \"%s\" in class %@", name, self];
break;
}
char types[5];
snprintf(types, 4, "%c@:", type);
// 新增方法
class_addMethod([self class], getterSel, getterImp, types);
snprintf(types, 5, "v@:%c", type);
// 新增方法
class_addMethod([self class], setterSel, setterImp, types);
}
free(properties);
}
複製程式碼其中property_getAttributes(property)獲取到的property屬性字串的第二位的型別資訊可以參考Apple官方文件
對應的程式中定義了TypeEncodings列舉
enum TypeEncodings {
Char = 'c',
Bool = 'B',
Short = 's',
Int = 'i',
Long = 'l',
LongLong = 'q',
UnsignedChar = 'C',
UnsignedShort = 'S',
UnsignedInt = 'I',
UnsignedLong = 'L',
UnsignedLongLong = 'Q',
Float = 'f',
Double = 'd',
Object = '@'
};
複製程式碼比如物件型別的屬性，經過如下的處理
getterImp = (IMP)objectGetter;
setterImp = (IMP)objectSetter;
//...
class_addMethod([self class], getterSel, getterImp, types);
class_addMethod([self class], setterSel, setterImp, types);
複製程式碼使用屬性Getter或者Setter最終會呼叫以下的方法
static id objectGetter(GVUserDefaults *self, SEL _cmd) {
NSString *key = [self defaultsKeyForSelector:_cmd];
return [self.userDefaults objectForKey:key];
}
static void objectSetter(GVUserDefaults *self, SEL _cmd, id object) {
NSString *key = [self defaultsKeyForSelector:_cmd];
if (object) {
[self.userDefaults setObject:object forKey:key];
} else {
[self.userDefaults removeObjectForKey:key];
}
}
複製程式碼這裡用到的defaultsKeyForSelector方法定義如下，把屬性Getter或者Setter方法對映為對應的屬性的儲存的Key的字串，同一個屬性的Getter或者Setter方法在self.mapping對應的值是一樣的，詳細的儲存對映資訊到self.mapping中可以檢視generateAccessorMethods方法。
- (NSString *)defaultsKeyForSelector:(SEL)selector {
return [self.mapping objectForKey:NSStringFromSelector(selector)];
}
複製程式碼isa Swizzling
系統的KVO的實現是基於isa swizzling實現的，建立一個NSObject的分類模擬KVO的實現，主要用到技術點
objc_allocateClassPair新增一個類objc_registerClassPair註冊新增的類object_setClass修改當前類的class，也就是isa指標class_addMethod類動態新增方法objc_msgSend使用底層C的方法執行方法呼叫objc_setAssociatedObject、objc_getAssociatedObject設定和獲取關聯物件
主要的思路如下：
- (void)ytt_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context方法是類似系統新增KVO監聽的方法，該方法中- 儲存
observer和keyPath引數；動態的建立和註冊KVO類； - 使用
object_setClass修改當前物件的isa指標； class_addMethod動態新增一個監聽的keyPath屬性對應的Setter方法
- 儲存
keyPath屬性對應的Setter方法的實現：- 使用
object_setClass修改物件的isa指標為原始的類，後面使用Setter方法設定新值呼叫的objc_msgSend方法才能正確執行； - 使用
objc_getAssociatedObject獲取繫結的關聯物件中keyPath，還原出Getter方法和Setter方法，使用Getter方法獲取舊的值，使用Setter方法設定新值； - 使用
objc_getAssociatedObject獲取繫結的關聯物件中observer，向 observer 物件傳送屬性變換的訊息； - 最後重置物件的
isa指標為動態建立的KVO類，下一次的流程才能正常執行
- 使用
@implementation NSObject (YTT_KVO)
- (void)ytt_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context {
// 儲存keypath
objc_setAssociatedObject(self, "keyPath", keyPath, OBJC_ASSOCIATION_COPY_NONATOMIC);
objc_setAssociatedObject(self, "observer", observer, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
// 獲取當前類
Class selfClass = self.class;
// 動態建立KVO類
const char * className = NSStringFromClass(selfClass).UTF8String;
char kvoClassName[1000];
sprintf(kvoClassName, "%s%s", "YTT_KVO_", className);
Class kvoClass = objc_allocateClassPair(selfClass, kvoClassName, 0);
if (!kvoClass) {
// Nil if the class could not be created (for example, the desired name is already in use).
kvoClass = NSClassFromString([NSString stringWithUTF8String:kvoClassName]);
}
objc_registerClassPair(kvoClass);
// 修改當前類指向為動態建立的KVO子類，kvoClass繼承自selfClass
object_setClass(self, kvoClass);
// 動態新增一個方法:setXxx()
SEL sel = NSSelectorFromString([NSString stringWithFormat:@"set%@:", keyPath.capitalizedString]);
class_addMethod(kvoClass, sel, (IMP)setValue, NULL);
}
void setValue(id self, SEL _cmd, id value) {
// 儲存當前的Class，重置Class使用
Class selfClass = [self class];
// 設定Class為原始Class
object_setClass(self, [self superclass]);
// 獲取keyPath
NSString* keyPath = objc_getAssociatedObject(self, "keyPath");
// KVO 回撥引數
NSMutableDictionary* change = [NSMutableDictionary dictionary];
change[NSKeyValueChangeNewKey] = value;
// 獲取舊的值
SEL getSel = NSSelectorFromString([NSString stringWithFormat:@"%@", keyPath]);
if ([self respondsToSelector:getSel]) {
id ret = ((id(*)(id, SEL, id))objc_msgSend)(self, getSel, value);
if (ret) {
change[NSKeyValueChangeOldKey] = ret;
}
}
// 給原始類設定資料
SEL setSel = NSSelectorFromString([NSString stringWithFormat:@"set%@:", keyPath.capitalizedString]);
if ([self respondsToSelector:setSel]) {
((void(*)(id, SEL, id))objc_msgSend)(self, setSel, value);
}
// 傳送通知
id observer = objc_getAssociatedObject(self, "observer");
SEL observerSel = @selector(ytt_observeValueForKeyPath:ofObject:change:context:);
if ([observer respondsToSelector:observerSel]) {
((void(*) (id, SEL, NSString*, id, id ,id))(void *)objc_msgSend)(observer, observerSel, keyPath, self, change, nil);
}
// 重置class指標，這樣再次呼叫物件方法會走到這裡面
object_setClass(self, selfClass);
}
@end
複製程式碼訊息轉發
訊息轉發的步驟有以下四個：
- 動態方法解析：
resolveClassMethod:(SEL)sel和resolveInstanceMethod:(SEL)sel處理類方法和例項方法，可以在該方法中使用class_addMethod動態新增方法處理，返回YES表示該步驟可處理，否則表示不可處理，繼續執行下一步 - 備援接收者：
forwardingTargetForSelector:(SEL)aSelector方法返回一個可以處理該訊息的物件完成訊息的轉發處理 - 完整的訊息轉發：
forwardInvocation:(NSInvocation *)anInvocation，如果以上兩個步驟都不能處理，最終會執行到這一步，anInvocation物件包含了訊息詳細資訊，包括id target、SEL selector、引數和返回值資訊等等。該方法需要和methodSignatureForSelector:(SEL)aSelector方法一起使用，可以使用NSInvocation的例項方法invokeWithTarget:(id)target完成訊息的轉發 - 如果以上的步驟都不能處理，最終會由
NSObject的方法doesNotRecognizeSelector:(SEL)aSelector，丟擲一個unrecognized selector sent to instance xxx的異常
GVUserDefaults 是一個屬性和NSUserDefaults之間實現自動寫入和讀取的開源庫，該庫（0.4.1之前的舊版本）使用到的技術就是訊息轉發
GVUserDefaults庫中使用的是訊息轉發中的動態方法解析resolveInstanceMethod方法，Setter方法的訊息轉發給accessorSetterC函式處理，Getter方法的訊息轉發給accessorGetterC函式處理，accessorSetter和accessorGetter最終還是通過NSUserDefaults實現屬性對應的Key的設定和讀取，關鍵的程式碼如下：
+ (BOOL)resolveInstanceMethod:(SEL)aSEL {
NSString *method = NSStringFromSelector(aSEL);
if ([method isEqualToString:@"transformKey:"] || [method isEqualToString:@"setupDefaults"]) {
// Prevent endless loop for optional (and missing) category methods
return [super resolveInstanceMethod:aSEL];
}
if ([method hasPrefix:@"set"]) {
class_addMethod([self class], aSEL, (IMP) accessorSetter, "v@:@");
return YES;
} else {
class_addMethod([self class], aSEL, (IMP) accessorGetter, "@@:");
return YES;
}
}
- (NSString *)_transformKey:(NSString *)key {
if ([self respondsToSelector:@selector(transformKey:)]) {
return [self performSelector:@selector(transformKey:) withObject:key];
}
return key;
}
id accessorGetter(GVUserDefaults *self, SEL _cmd) {
NSString *key = NSStringFromSelector(_cmd);
key = [self _transformKey:key];
return [[NSUserDefaults standardUserDefaults] objectForKey:key];
}
void accessorSetter(GVUserDefaults *self, SEL _cmd, id newValue) {
NSString *method = NSStringFromSelector(_cmd);
NSString *key = [[method stringByReplacingCharactersInRange:NSMakeRange(0, 3) withString:@""] stringByReplacingOccurrencesOfString:@":" withString:@""];
key = [key stringByReplacingCharactersInRange:NSMakeRange(0,1) withString:[[key substringToIndex:1] lowercaseString]];
key = [self _transformKey:key];
// Set value of the key anID to newValue
[[NSUserDefaults standardUserDefaults] setObject:newValue forKey:key];
}
複製程式碼