Runtime精進
一、什麼是runtime
runtime是一套用C語言和彙編寫的一套API,存在意義是支持OC動態性,將一些工作編譯連接推遲到運行時,只有編譯器是不夠的,還需要一個運行時系統,這就是runtime機制。其中最主要的就是消息機制。 消息轉發和消息傳遞。
使用場景
注意事項
- swizzling應該總在+load中執行
- swizzling應該總是在dispatch_once中執行
- +load中調用的時候,不要調用[super load]多次調用,會出現無效的假象
- 避免swizzling代碼被重複執行,可以通過GCD的dipatch_once函數來解決,利用dispatch_once函數內代碼只會執行一次的特性。
1.UI控件防止短時間內重複點擊
實現思路: 1.動態添加兩個屬性,添加對應set,get方法 根據情況判斷定條件
2. 是否ignore
3. 間隔時間
#import "UIControl+Limit.h"
#import <objc/runtime.h>
// 設置控件不能連續點擊間隔
// 熟悉使用的相關控件
static const char *UIControl_acceptEventInternal = "UIControl_acceptEventInternal";
static const char *UIControl_ignoreEvent = "UIControl_ignoreEvent";
@implementation UIControl (Limit)
#pragma mark - acceptEventInternal
//動態添加類型
// set方法
- (void)setAcceptEventInterval:(NSTimeInterval)acceptEventInterval {
// 動態設置新屬性
objc_setAssociatedObject(self, UIControl_acceptEventInternal, @(acceptEventInterval), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
//get方法
- (NSTimeInterval)acceptEventInterval {
return [objc_getAssociatedObject(self, UIControl_acceptEventInternal) doubleValue];
}
#pragma mark -ignoreEvent
- (void)setIgnoreEvent:(NSTimeInterval)ignoreEvent {
objc_setAssociatedObject(self, UIControl_ignoreEvent, @(ignoreEvent), OBJC_ASSOCIATION_ASSIGN);
}
- (NSTimeInterval)ignoreEvent {
return [objc_getAssociatedObject(self, UIControl_ignoreEvent) boolValue];
}
#pragma mark - Swizzling
+ (void)load {
Method a = class_getInstanceMethod(self, @selector(sendAction:to:forEvent:));
Method b = class_getInstanceMethod(self, @selector(swizzled_sendAction:to:forEvent:));
method_exchangeImplementations(a, b); // 交換方法
}
- (void)swizzled_sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event {
if (self.ignoreEvent) { // 忽略事件
NSLog(@"btnAction is intercepted");
return;
}
if (self.acceptEventInterval >0) {
self.ignoreEvent = YES;
[self performSelector:@selector(setIgnoreEventWithNo) withObject:nil afterDelay:self.acceptEventInterval];
}
[self swizzled_sendAction:action to:target forEvent:event];
}
- (void)setIgnoreEventWithNo {
self.ignoreEvent = NO;
}
@end
2.防止數組越界
NSNumber,NSArray,NSDictionary這些類族無效。
#import "NSArray+CrashHandle.h"
#import <objc/runtime.h>
//使用runtime解決數組越界問題
// 1.對應d類族 替換到真身對應方法
@implementation NSArray (CrashHandle)
+ (void)load {
//交換系統方法
Method fromMethod = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(objectAtIndex:));
Method toMethod = class_getInstanceMethod(objc_getClass("__NSArrayI"), @selector(cm_objectAtIndex:));
method_exchangeImplementations(fromMethod, toMethod);
}
-(id)cm_objectAtIndex:(NSUInteger)index {
if (self.count -1 < index) {
//數組越界
@try {
return [self cm_objectAtIndex:index];
} @catch (NSException *exception) {
//崩潰後打印崩潰信息,如果線上,這裏將崩潰信息發送到服務器
NSLog(@"----------%s Crash Because Method %s---------\n", class_getName(self.class), __func__);
// NSLog(@"%@"m [exception callStack])
return nil;
} @finally {
}
} else {
return [self cm_objectAtIndex:index];
}
}
@end
3. 統計VC加載次數
load類方法是程序運行時這個類被加載到內存中就調用的一個方法,執行比較早,不需要我們手動調用。
#import "UIViewController+Logging.h"
#import <objc/runtime.h>
@implementation UIViewController (Logging)
//類加載的時候會被執行
+(void)load {
swizzleMehod([self class], @selector(viewDidAppear:), @selector(swizzle_viewDidAppear:));
}
// 交換方法
- (void)swizzle_viewDidAppear:(BOOL)animated {
[self swizzle_viewDidAppear:animated];
//Logging
NSLog(@" - %@",NSStringFromClass([self class])); //打印當前類型名稱
}
//交換方法
void swizzleMehod(Class class, SEL originalSelector, SEL swizzledSelector) {
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
if(didAddMethod) {
class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, swizzledMethod);
}
}
@end
用法一:交換類的方法
實現load類方法 — 類加載運行的時候就會調用
消息傳遞
掌握對應的數據結構 OC函數調用都會轉化成objc_msgSend(id self, SEL op, …)函數
查看幾個對應結構體熟悉概念
類對象(objc_class):單例,在編譯期產生用於創建實例對象
類實例(objc_object)
元類(Meta Class)
Mehod (objc_method)
SEL (objc_selector)
IMP
類緩存 (objc_cache)
Category (objc_category)
//對象
struct objc_object {
Class isa OBJC_ISA_AVAILABILITY;
};
//類
struct objc_class {
Class isa OBJC_ISA_AVAILABILITY;
#if !__OBJC2__
Class super_class OBJC2_UNAVAILABLE;
const char *name OBJC2_UNAVAILABLE;
long version OBJC2_UNAVAILABLE;
long info OBJC2_UNAVAILABLE;
long instance_size OBJC2_UNAVAILABLE;
struct objc_ivar_list *ivars OBJC2_UNAVAILABLE;
struct objc_method_list **methodLists OBJC2_UNAVAILABLE;
struct objc_cache *cache OBJC2_UNAVAILABLE;
struct objc_protocol_list *protocols OBJC2_UNAVAILABLE;
#endif
} OBJC2_UNAVAILABLE;
//方法列表
struct objc_method_list {
struct objc_method_list *obsolete OBJC2_UNAVAILABLE;
int method_count OBJC2_UNAVAILABLE;
#ifdef __LP64__
int space OBJC2_UNAVAILABLE;
#endif
/* variable length structure */
struct objc_method method_list[1] OBJC2_UNAVAILABLE;
} OBJC2_UNAVAILABLE;
//方法
struct objc_method {
SEL method_name OBJC2_UNAVAILABLE;
char *method_types OBJC2_UNAVAILABLE;
IMP method_imp OBJC2_UNAVAILABLE;
}
幾個步驟:
- 系統先找到消息的接受對象,通過對象的isa 找到它的類
- 類中查找method_list,是否有selector方法
- 沒有查找父類的method_list
- 找到對應的method,執行它的IMP
- 轉發IMP的return 值
消息轉發
消息轉發失敗反覆會執行doesNotRecognizeSelector: 方法報unregnized selector
完整的轉發流程: resolveInstance forwardTarget forwardInvacation
#import "ViewController.h"
#import "objc/runtime.h"
@interface Person: NSObject
@end
@implementation Person
- (void)foo {
NSLog(@"Doing foo");//Person的foo函數
}
@end
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
//執行foo函數
[self performSelector:@selector(foo)];
}
+ (BOOL)resolveInstanceMethod:(SEL)sel {
return YES;//返回YES,進入下一步轉發
}
- (id)forwardingTargetForSelector:(SEL)aSelector {
return nil;//返回nil,進入下一步轉發
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
if ([NSStringFromSelector(aSelector) isEqualToString:@"foo"]) {
return [NSMethodSignature signatureWithObjCTypes:"v@:"];//簽名,進入forwardInvocation
}
return [super methodSignatureForSelector:aSelector];
}
- (void)forwardInvocation:(NSInvocation *)anInvocation {
SEL sel = anInvocation.selector;
Person *p = [Person new];
if([p respondsToSelector:sel]) {
[anInvocation invokeWithTarget:p];
}
else {
[self doesNotRecognizeSelector:sel];
}
}
@end
runtime應用
大型框架的利器,應用場景
- 關聯對象
- 方法魔法
- 消息轉發熱更解決bug
- 實現NScoding的自動歸檔和自動接檔
- 實現字典和模型的自動轉換
1.關聯對象
相關API
void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy) //獲取關聯的對象 id objc_getAssociatedObject(id object, const void *key) //移除關聯的對象 void objc_removeAssociatedObjects(id object)
demo展示
@interface UIView (DefaultColor)
@property (nonatomic, strong) UIColor *defaultColor;
@end
@implementation UIView (DefaultColor)
@dynamic defaultColor;
static char kDefaultColorKey;
- (void)setDefaultColor:(UIColor *)defaultColor {
objc_setAssociatedObject(self, &kDefaultColorKey, defaultColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (id)defaultColor {
return objc_getAssociatedObject(self, &kDefaultColorKey);
}
@end
2.方法魔法
class_addMethod([self class], sel, (IMP)fooMethod, "v@:");`
-
cls 被添加方法的類
-
name 添加的方法的名稱的SEL
-
imp 方法的實現。該函數必須至少要有兩個參數,self,_cmd
類型編碼 -
方法交換
+ (void)load {
//原子操作確保在不同的線程中代碼只執行了一次。 dispatch_once滿足了需求 swizzleing 改變了全局的轉檯,確保每個預防措施在運行時都是可用的。
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
Class class = [self class];
SEL originalSelector = @selector(viewDidLoad);
SEL swizzledSelector = @selector(jkviewDidLoad);
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
if (didAddMethod) {//添加成成功
class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, swizzledMethod); //交換兩個方法
}
});
}
- (void)jkviewDidLoad {
NSLog(@"替換的方法");
[self jkviewDidLoad];
}
swizzling 應該只在+load(一個類被初始裝載時調用)中完成,+initialize 是在應用調用該類的類方法或實例方法前調用的,在Objective-c 的運行時中,
KVO實現
1.Apple使用了isa-swizzling 來實現KVO,動態機制創建一個新的名爲:NSKVONotifying_A的新類
NSCoding 使用
數據寫到硬盤上的時候,將數據序列化然後轉化爲二進制文件從而便於在磁盤上讀寫。讀取的時候進行反序列化。
//實現NSCoding的自動歸檔和自動接檔
- (id)initWithCoder:(NSCoder *)aDecoder {
if (self = [super init]) {
unsigned int outCount;
Ivar *ivars = class_copyIvarList([self class], &outCount); // 獲取對象屬性列表
for (int i = 0; i< outCount; ++i) {
Ivar ivar = ivars[i];
NSString *key = [NSString stringWithUTF8String:ivar_getName(ivar)]; //得到屬性utf8字符串編碼
[self setValue:[aDecoder decodeObjectForKey:key] forKey:key];
}
}
return self;
}
- (void)encodeWithCoder:(NSCoder *)aCoder {
unsigned int outCount;
Ivar *ivars = class_copyIvarList([self class], &outCount);
for (int i = 0; i< outCount; ++i) {
Ivar ivar = ivars[i];
NSString * key = [NSString stringWithUTF8String:ivar_getName(ivar)];
[aCoder encodeObject:[self valueForKey:key] forKey:key];
}
}
實現字典和模型的自動轉換
// 字典和模型的自動轉換(MJExtension)
// 實現原理:用runtime提供的函數遍歷modeld自身所有屬性,如果屬性在jsonz中存在,則將其賦值
// 熟悉使用到相關函數 s熟悉對應提供的API接口 熟悉對應英文
- (instancetype)initWithDict:(NSDictionary *)dict {
if (self = [super init]) {
// 獲取類的屬性及屬性對應的類型
NSMutableArray *keys = [NSMutableArray array];
NSMutableArray *attributes = [NSMutableArray array];
unsigned int outCount;
objc_property_t *properties = class_copyPropertyList([self class], &outCount);
for (int i = 0; i< outCount; ++i) {
objc_property_t property = properties[i];
// 通過property_getName 函數獲取屬性的名字
NSString *propertyName = [NSString stringWithCString:property_getName(property) encoding:NSUTF8StringEncoding];
[keys addObject:propertyName];
// 通過propety_getAttribute函數獲取屬性的名字和@encode編碼
NSString *propertyAttribute = [NSString stringWithCString:property_getAttributes(property) encoding:NSUTF8StringEncoding];
[attributes addObject:propertyAttribute];
}
// 立即釋放properties指向的內存
free(properties);
// 根據類型給屬性賦值
for (NSString *key in keys) {
if ([dict valueForKey:key] == nil) continue;
// dict包含對應字段
[self setValue:[dict valueForKey:key] forKey:key];
}
}
return self;
}
怎樣會站在作者的角度得出同樣的結論?
提升點
- 熟悉對應頭文件API 熟悉對應文檔
關鍵點: 消息傳遞 消息轉發 對應應用
大家的總結似乎都是一樣
很多作者寫的內容看起來 邏輯很不經推敲,沒有一個比較完善的思維模型,大部分都是抄襲來的,很多知識都幫助不了讀者建立一個連貫的理解或者是樹狀發散效果,只是更多知識的堆砌。