Objective-C Runtime运行时之Method Sw

直接进入正题~

相信大家应该都见过Method Swizzling的标准模板，举个 一缕殇流化隐半边冰霜 大神文中的例子：

@implementation UIViewController (Swizzling)
+ (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);
        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);
        }
    });
}

这里提到一句话

一般我们使用都是新建一个分类，在分类中进行Method Swizzling方法的交换。

可是如果我并不是在新建的Category 中，那么可能就要换一种写法了。

首先来分析一下上面获取Method的两句代码

Method originalMethod = class_getInstanceMethod(class, originalSelector);

Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

由于一般都是新建Category，所以这里的class其实就是分类自己的class，而且由于是Category，所以UIViewController也会拿到swizzledSelector，那么这两个Method都可以拿到。但是，我现在如果新建了一个和UIViewController 无关的targetClass类，那么UIViewController就拿不到swizzledSelector，进一步swizzledMethod也就变成了nil。这就坑爹了……

那么想一想该怎么解决这个问题。既然UIViewController拿不到，那我就把这个selector加给你好了。用下面的方法：

Method targetMethod = class_getInstanceMethod(targetClass, targetSelector);

IMP targetIMP = class_getMethodImplementation(targetClass ,targetSelector);

BOOL didAddMethod = class_addMethod(originalClass, targetSelector, targetIMP, method_getTypeEncoding(targetMethod));

注意这里和常见模板的不同之处，常见模板class_addMethod是这样的：

BOOL didAddMethod=class_addMethod(class

,originalSelector

,method_getImplementation(swizzledMethod)

,method_getTypeEncoding(swizzledMethod));

而现在要做的是不但把Method加过去，还要把targetSeletor加过去。而且后续的可是这样做又带来一个问题是，如果我要把这个模板函数定义成一个通用方法，让所有类都能调用的话，就要区分是否Category。而且还有一个问题是，为了确保方法只被swizzling一次，一般都在load函数里面写个dispatch_once。但是如果漏写了呢？我想要的是通用方法啊。

下面给出的是我摸索出来的模板：

NS_INLINE void ETrackingHookingMethod(Class originalClass, Class targetClass, SEL originalSelector){
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wundeclared-selector"
    SEL targetSelector = NSSelectorFromString([NSString stringWithFormat:@"etracking_%@", NSStringFromSelector( originalSelector)]);
#pragma clang diagnostic pop
    static NSMutableSet * allHookedClass = nil;
    if (allHookedClass == nil) {
        allHookedClass = [NSMutableSet set];
    }
    if (!originalClass){
        return;
    }else{
        NSString *hookedSelector = [NSString stringWithFormat:@"%@_%@",NSStringFromClass(originalClass),NSStringFromSelector(originalSelector)];
        if (![allHookedClass containsObject:hookedSelector]) {
            [allHookedClass addObject:hookedSelector];
        }else{
            return;
        }

    }
    NSLog(@"allhookClass%@",allHookedClass);
    Method originalMethod = class_getInstanceMethod(originalClass, originalSelector);
    Method targetMethod = class_getInstanceMethod(targetClass, targetSelector);
    if ((!targetMethod) || (!originalMethod)) {
        return;
    }
    
    Method hasTargetMethod = class_getInstanceMethod(originalClass, targetSelector);
    
    IMP targetIMP = class_getMethodImplementation(targetClass ,targetSelector);
    
    BOOL didAddMethod = NO;
    if (originalClass == targetClass) {
        didAddMethod = class_addMethod(originalClass,originalSelector,method_getImplementation(targetMethod),method_getTypeEncoding(targetMethod));
        if (didAddMethod) {
            IMP replacedMethod = class_replaceMethod(originalClass,
                                targetSelector,
                                method_getImplementation(originalMethod),
                                method_getTypeEncoding(originalMethod));
        }else{
            method_exchangeImplementations(originalMethod, targetMethod);
        }
    }else{
        if (hasTargetMethod) {
            return;
        }else{
            didAddMethod =  class_addMethod(originalClass, targetSelector, targetIMP, method_getTypeEncoding(targetMethod));
            
            Method originTargetMethod = class_getInstanceMethod(originalClass, targetSelector);
            BOOL hasSource = class_respondsToSelector(originalClass, originalSelector);
            BOOL hasTarget = class_respondsToSelector(targetClass, targetSelector);
            if (hasSource && hasTarget) {
                method_exchangeImplementations(originalMethod,originTargetMethod);
            }
        }
    }
}

关于hook UITableViewDelegate 的，可以新建一个类，在load方法里面调用

+(void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        ETrackingHookingMethod([UITableView class], [ETrackingTableViewExplorer class], @selector(setDelegate:));
    });
}

先hook到setDelegate：方法，然后在自己类中这么处理（这里比较猥琐了）：

-(void)etracking_setDelegate:(id)delegate{
    Class conformClass = [delegate class];
    while ([conformClass conformsToProtocol:@protocol(UITableViewDelegate)]) {
        Class  superConformClass = class_getSuperclass(conformClass);
        if ([superConformClass conformsToProtocol:@protocol(UITableViewDelegate)]) {
            conformClass = superConformClass;
        }else{
            break;
        }
    }
    ETrackingHookingMethod(conformClass,[ETrackingTableViewExplorer class],@selector(tableView:didSelectRowAtIndexPath:));
    ETrackingHookingMethod(conformClass,[ETrackingTableViewExplorer class],@selector(tableView:cellForRowAtIndexPath:));
    [self etracking_setDelegate:delegate];
}

这样你就可以随意新增想要hook的方法了。同理这样可以处理自己类中的appDelegate，collectionDelegate等等一系列方法。

参考文章：
南峰子的技术博客
一缕殇流化隐半边冰霜