Runtime合集 iOS - Runtime基础

1. Method Swizzling是什么

通常我们叫它方法交换或方法欺骗 Method Swizzling用于改变一个已经存在的selector实现，在程序运行时，通过改变selector和所在类的methodLists 的映射从而改变方法的调用。其实质就是交换两个方法的IMP(方法实现)

上篇文章我们知道:Method（方法）对应的是objc_Method结构体，而objc_method结构体中包含了SEL method_name（方法名）和IMP（方法实现）

struct objc_method {
    SEL _Nonnull method_name;
    char * _Nullable method_types;
    IMP _Nonnull method_imp;
};

Method（方法）、SEL（方法名）、IMP（方法实现）三者的关系可以这样来表示: 在运行时，Class（类）维护了一个method list（方法列表）来确定消息的正确发送。method list（方法列表）存放的元素就是Method（方法）。而Method（方法）中映射了一对键值对：SEL（方法名）：IMP（方法实现）。 Method Swizzling修改了method list（方法列表），使得不同Method（方法）中的键值对发生了交换。比如交换前两个键值对分别为SEL A ：IMP A、SEL B ：IMP B，交换之后就变成了SEL A ：IMP B、SEL B ： IMP A 如图所示: Swizzling 交换示意图

2. Method Swizzling 底层源码

(Runtime源码下载)[opensource.apple.com/tarballs/ob…] 源码位于objc-class-old.m

void method_exchangeImplementations(Method m1_gen, Method m2_gen)
{
    IMP m1_imp;
    old_method *m1 = oldmethod(m1_gen);
    old_method *m2 = oldmethod(m2_gen);
    if (!m1  ||  !m2) return;

    impLock.lock();
    m1_imp = m1->method_imp;
    m1->method_imp = m2->method_imp;
    m2->method_imp = m1_imp;
    impLock.unlock();
}

或 objc-runtime-new.m

void method_exchangeImplementations(Method m1, Method m2)
{
    if (!m1  ||  !m2) return;

    mutex_locker_t lock(runtimeLock);

    IMP imp1 = m1->imp(false);
    IMP imp2 = m2->imp(false);
    SEL sel1 = m1->name();
    SEL sel2 = m2->name();

    m1->setImp(imp2);
    m2->setImp(imp1);


    // RR/AWZ updates are slow because class is unknown
    // Cache updates are slow because class is unknown
    // fixme build list of classes whose Methods are known externally?

    flushCaches(nil, __func__, [sel1, sel2, imp1, imp2](Class c){
        return c->cache.shouldFlush(sel1, imp1) || c->cache.shouldFlush(sel2, imp2);
    });

    adjustCustomFlagsForMethodChange(nil, m1);
    adjustCustomFlagsForMethodChange(nil, m2);
}

2. Method Swizzling使用方法

+ (void)swizzlingInClass:(Class)cls originalSelector:(SEL)originalSelector swizzledSelector:(SEL)swizzledSelector {
    
    Class msclass = cls;
    Method originalMethod = class_getInstanceMethod(msclass, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(msclass, swizzledSelector);
    BOOL didAddMethod =
    class_addMethod(msclass,
                    originalSelector,
                    method_getImplementation(swizzledMethod),
                    method_getTypeEncoding(swizzledMethod));
    if (didAddMethod) {
        class_replaceMethod(msclass,
                            swizzledSelector,
                            method_getImplementation(originalMethod),
                            method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}

3. Method Swizzling 使用注意事项

应该只在 +load 中执行 Method Swizzling 程序在启动的时候，会先加载所有的类，这时会调用每个类的 +load 方法。而且在整个程序运行周期只会调用一次（不包括外部显示调用)。所以在 +load 方法进行 Method Swizzling 再好不过了。

而为什么不用 +initialize 方法呢。

因为 +initialize 方法的调用时机是在第一次向该类发送第一个消息的时候才会被调用。如果该类只是引用，没有调用，则不会执行 +initialize 方法。 Method Swizzling 影响的是全局状态，+load 方法能保证在加载类的时候就进行交换，保证交换结果。而使用 +initialize 方法则不能保证这一点，有可能在使用的时候起不到交换方法的作用。

Method Swizzling 在 +load 中执行时，不要调用 [super load];。

上边我们说了，程序在启动的时候，会先加载所有的类。如果在 + (void)load方法中调用 [super load] 方法，就会导致父类的 Method Swizzling 被重复执行两次，而方法交换也被执行了两次，相当于互换了一次方法之后，第二次又换回去了，从而使得父类的 Method Swizzling 失效。

Method Swizzling 应该总是在 dispatch_once 中执行 Method Swizzling 不是原子操作，dispatch_once 可以保证即使在不同的线程中也能确保代码只执行一次。所以，我们应该总是在 dispatch_once 中执行 Method Swizzling 操作，保证方法替换只被执行一次。

4. Method Swizzling 应用场景

Method Swizzling 可以交换两个方法的实现，在开发中更多的是应用于系统类库，以及第三方框架的方法替换。在官方不公开源码的情况下，我们可以借助 Runtime 的 Method Swizzling 为原有方法添加额外的功能

4.1 全局页面统计功能

@implementation UIViewController (HIAnalysis)

+ (void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        
        SEL originalSelector = @selector(viewDidLoad);
        SEL swizzledSelector = @selector(analysis_viewDidLoad);
        [HIHookUtility swizzlingInClass:[self class] originalSelector:originalSelector swizzledSelector:swizzledSelector];
        
        originalSelector = @selector(viewWillAppear:);
        swizzledSelector = @selector(analysis_viewWillAppear:);
        [HIHookUtility swizzlingInClass:[self class] originalSelector:originalSelector swizzledSelector:swizzledSelector];
        
        originalSelector = @selector(viewDidAppear:);
        swizzledSelector = @selector(analysis_viewDidAppear:);
        [HIHookUtility swizzlingInClass:[self class] originalSelector:originalSelector swizzledSelector:swizzledSelector];
        
        originalSelector = @selector(viewWillDisappear:);
        swizzledSelector = @selector(analysis_viewWillDisappear:);
        [HIHookUtility swizzlingInClass:[self class] originalSelector:originalSelector swizzledSelector:swizzledSelector];
        
        originalSelector = @selector(viewDidDisappear:);
        swizzledSelector = @selector(analysis_viewDidDisappear:);
        [HIHookUtility swizzlingInClass:[self class] originalSelector:originalSelector swizzledSelector:swizzledSelector];
    });
}

- (void)analysis_viewDidLoad{
    
    [self analysis_viewDidLoad];
}

- (void)analysis_viewWillAppear:(BOOL)animated{
    
    void(^fetchTitleHandler)(void) = ^(){
        NSString *title = self.title;
        if (!isStrEmpty(title) &&
            ![self isKindOfClass:[UINavigationController class]] &&
            ![self isKindOfClass:[UITabBarController class]]) {
            [HIAppAnalytics HI_trackPageBegin:title];
        }
    };
    
    if ([self respondsToSelector:@selector(analysisName)]) {
        NSString *analysisName = [self performSelector:@selector(analysisName)];
        if (!isStrEmpty(analysisName)) {
            [HIAppAnalytics HI_trackPageBegin:analysisName];
        }else{
            fetchTitleHandler();
        }
    }else{
        fetchTitleHandler();
    }
    
    
    [self analysis_viewWillAppear:animated];
}

4. 2 字体根据屏幕尺寸适配

为 UIFont 建立一个 Category。
在分类中实现一个自定义的 xxx_systemFontOfSize: 方法，在其中添加缩放字体的方法。
利用 Method Swizzling 将 systemFontOfSize: 方法和 xxx_systemFontOfSize: 进行方法交换。

#import "UIFont+AdjustSwizzling.h"
#import <objc/runtime.h>

#define XXX_UISCREEN_WIDTH  375

@implementation UIFont (AdjustSwizzling)

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // 类方法存储在元类对象中，我们通过 object_getClass 获取 self.isa 所指向的元类
        Class class = object_getClass((id)self);

        SEL originalSelector = @selector(systemFontOfSize:);
        SEL swizzledSelector = @selector(xxx_systemFontOfSize:);

        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);
        }
    });
}

+ (UIFont *)xxx_systemFontOfSize:(CGFloat)fontSize {
    UIFont *newFont = nil;
    newFont = [UIFont xxx_systemFontOfSize:fontSize * [UIScreen mainScreen].bounds.size.width / XXX_UISCREEN_WIDTH];
    
    return newFont;
}

@end

4.3 全局处理按钮重复点击

为 UIControl 或 UIButton 建立一个 Category。
在分类中添加一个 NSTimeInterval xxx_acceptEventInterval; 的属性，设定重复点击间隔
在分类中实现一个自定义的 xxx_sendAction:to:forEvent: 方法，在其中添加限定时间相应的方法。
利用 Method Swizzling 将 sendAction:to:forEvent: 方法和 xxx_sendAction:to:forEvent: 进行方法交换。

#import "UIButton+DelaySwizzling.h"
#import <objc/runtime.h>

@interface UIButton()

// 重复点击间隔
@property (nonatomic, assign) NSTimeInterval xxx_acceptEventInterval;
// 上一次点击时间戳
@property (nonatomic, assign) NSTimeInterval xxx_acceptEventTime;

@end


@implementation UIButton (DelaySwizzling)

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];

        SEL originalSelector = @selector(sendAction:to:forEvent:);
        SEL swizzledSelector = @selector(xxx_sendAction:to:forEvent:);

        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);
        }
    });
}

- (void)xxx_sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event {
    
    // 如果想要设置统一的间隔时间，可以在此处加上以下几句
    if (self.xxx_acceptEventInterval <= 0) {
        // 如果没有自定义时间间隔，则默认为 0.4 秒
        self.xxx_acceptEventInterval = 0.4;
    }
    
    // 是否小于设定的时间间隔
    BOOL needSendAction = (NSDate.date.timeIntervalSince1970 - self.xxx_acceptEventTime >= self.xxx_acceptEventInterval);
    
    // 更新上一次点击时间戳
    if (self.xxx_acceptEventInterval > 0) {
        self.xxx_acceptEventTime = NSDate.date.timeIntervalSince1970;
    }
    
    // 两次点击的时间间隔小于设定的时间间隔时，才执行响应事件
    if (needSendAction) {
        [self xxx_sendAction:action to:target forEvent:event];
    }
}

- (NSTimeInterval )xxx_acceptEventInterval{
    return [objc_getAssociatedObject(self, "UIControl_acceptEventInterval") doubleValue];
}

- (void)setXxx_acceptEventInterval:(NSTimeInterval)xxx_acceptEventInterval{
    objc_setAssociatedObject(self, "UIControl_acceptEventInterval", @(xxx_acceptEventInterval), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (NSTimeInterval )xxx_acceptEventTime{
    return [objc_getAssociatedObject(self, "UIControl_acceptEventTime") doubleValue];
}

- (void)setXxx_acceptEventTime:(NSTimeInterval)xxx_acceptEventTime{
    objc_setAssociatedObject(self, "UIControl_acceptEventTime", @(xxx_acceptEventTime), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end

4.4 TableView、CollectionView 异常加载占位图

为 TableView 建立一个 Category，Category 中添加刷新回调 block 属性、占位图 View 属性。在分类中实现一个自定义的 xxx_reloadData 方法，在其中添加判断是否为空，以及加载占位图、隐藏占位图的相关代码。利用 Method Swizzling 将 reloadData 方法和 xxx_reloadData 进行方法交换。

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface UITableView (ReloadDataSwizzling)

@property (nonatomic, assign) BOOL firstReload;
@property (nonatomic, strong) UIView *placeholderView;
@property (nonatomic,   copy) void(^reloadBlock)(void);

@end

/*--------------------------------------*/

#import "UITableView+ReloadDataSwizzling.h"
#import "XXXPlaceholderView.h"
#import <objc/runtime.h>

@implementation UITableView (ReloadDataSwizzling)


+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];

        SEL originalSelector = @selector(reloadData);
        SEL swizzledSelector = @selector(xxx_reloadData);

        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);
        }
    });
}

- (void)xxx_reloadData {
    if (!self.firstReload) {
        [self checkEmpty];
    }
    self.firstReload = NO;
    
    [self xxx_reloadData];
}


- (void)checkEmpty {
    BOOL isEmpty = YES; // 判空 flag 标示
    
    id <UITableViewDataSource> dataSource = self.dataSource;
    NSInteger sections = 1; // 默认TableView 只有一组
    if ([dataSource respondsToSelector:@selector(numberOfSectionsInTableView:)]) {
        sections = [dataSource numberOfSectionsInTableView:self] - 1; // 获取当前TableView 组数
    }
    
    for (NSInteger i = 0; i <= sections; i++) {
        NSInteger rows = [dataSource tableView:self numberOfRowsInSection:i]; // 获取当前TableView各组行数
        if (rows) {
            isEmpty = NO; // 若行数存在，不为空
        }
    }
    if (isEmpty) { // 若为空，加载占位图
        if (!self.placeholderView) { // 若未自定义，加载默认占位图
            [self makeDefaultPlaceholderView];
        }
        self.placeholderView.hidden = NO;
        [self addSubview:self.placeholderView];
    } else { // 不为空，隐藏占位图
        self.placeholderView.hidden = YES;
    }
}

- (void)makeDefaultPlaceholderView {
    self.bounds = CGRectMake(0, 0, self.frame.size.width, self.frame.size.height);
    XXXPlaceholderView *placeholderView = [[XXXPlaceholderView alloc] initWithFrame:self.bounds];
    __weak typeof(self) weakSelf = self;
    [placeholderView setReloadClickBlock:^{        if (weakSelf.reloadBlock) {            weakSelf.reloadBlock();        }    }];
    self.placeholderView = placeholderView;
}

- (BOOL)firstReload {
    return [objc_getAssociatedObject(self, @selector(firstReload)) boolValue];
}

- (void)setFirstReload:(BOOL)firstReload {
    objc_setAssociatedObject(self, @selector(firstReload), @(firstReload), OBJC_ASSOCIATION_ASSIGN);
}

- (UIView *)placeholderView {
    return objc_getAssociatedObject(self, @selector(placeholderView));
}

- (void)setPlaceholderView:(UIView *)placeholderView {
    objc_setAssociatedObject(self, @selector(placeholderView), placeholderView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (void (^)(void))reloadBlock {
    return objc_getAssociatedObject(self, @selector(reloadBlock));
}

- (void)setReloadBlock:(void (^)(void))reloadBlock {
    objc_setAssociatedObject(self, @selector(reloadBlock), reloadBlock, OBJC_ASSOCIATION_COPY_NONATOMIC);
}

@end

4.5 APM（应用性能管理）、防止程序崩溃

通过 Method Swizzling 替换 NSURLConnection , NSURLSession 相关的原始实现（例如 NSURLConnection 的构造方法和 start 方法），在实现中加入网络性能埋点行为，然后调用原始实现。从而来监控网络。防止程序崩溃，可以通过 Method Swizzling 拦截容易造成崩溃的系统方法，然后在替换方法捕获异常类型 NSException ，再对异常进行处理。最常见的例子就是拦截 arrayWithObjects:count: 方法避免数组越界

@implementation NSArray (ArrayBounds)
+ (void)load{
    [super load];
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{  //方法交换只要一次就好
        
        //替换 objectAtIndex
        NSString *tmpStr = @"objectAtIndex:";
        NSString *tmpFirstStr = @"safe_ZeroObjectAtIndex:";
        NSString *tmpThreeStr = @"safe_objectAtIndex:";
        NSString *tmpSecondStr = @"safe_singleObjectAtIndex:";
        
        // 替换 objectAtIndexedSubscript
        
        NSString *tmpSubscriptStr = @"objectAtIndexedSubscript:";
        NSString *tmpSecondSubscriptStr = @"safe_objectAtIndexedSubscript:";
        
        [HIHookUtility swizzlingInClass:NSClassFromString(@"__NSArray0") originalSelector:NSSelectorFromString(tmpStr) swizzledSelector:NSSelectorFromString(tmpFirstStr)];
        
        [HIHookUtility swizzlingInClass:NSClassFromString(@"__NSSingleObjectArrayI") originalSelector:NSSelectorFromString(tmpStr) swizzledSelector:NSSelectorFromString(tmpSecondStr)];
        
        [HIHookUtility swizzlingInClass:NSClassFromString(@"__NSArrayI") originalSelector:NSSelectorFromString(tmpStr) swizzledSelector:NSSelectorFromString(tmpThreeStr)];
        
        [HIHookUtility swizzlingInClass:NSClassFromString(@"__NSArrayI") originalSelector:NSSelectorFromString(tmpSubscriptStr) swizzledSelector:NSSelectorFromString(tmpSecondSubscriptStr)];
        
    });
}

#pragma mark --- implement method

/**
 取出NSArray 第index个 值 对应 __NSArrayI
 
 @param index 索引 index
 @return 返回值
 */
- (id)safe_objectAtIndex:(NSUInteger)index {
    
    if (index > self.count - 1 || !self.count){
        @try {
            return [self safe_objectAtIndex:index];
        } @catch (NSException *exception) {
            //__throwOutException  抛出异常
            NSAssert(NO, @"---index越界！！！");
            NSLog(@"exception: %@", exception.reason);
            return nil;
        } @finally {
            
        }
    }else{
        
        return [self safe_objectAtIndex:index];
    }
}

参考『Runtime』详解（二）Method Swizzling

iOS - Runtime Method Swizzling