Runtime使用之埋点

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在需要统计用户行为的时候，传统点做法就是在需要统计的地方加入响应的代码，如viewWillAppear、viewWillDisappear和一些交互事件中。优雅一点可以自定义一个控制器让其它控制器继承。代码耦合，扩展性差，不易维护，这些都是上述的方法的一些弊端。昨天说的Runtime黑魔法可以很优雅方便地解决这些弊端。

具体实现

给UIViewController写个分类， + (void)load 这个类方法是在一个类被读到内存后，Runtime就会给它发送load消息，所以这个方法调用得很早，适合用来埋点。
下面混合每个UIViewController的viewDidAppear，也就是在执行原来的viewDidAppear之前先执行统计方法。

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#import "UIViewController+swizzling.h"
#import <objc/runtime.h>
 
@implementation UIViewController (swizzling)
 
+ (void)load
{
    SEL origSel = @selector(viewDidAppear:);
    SEL swizSel = @selector(swiz_viewDidAppear:);
    [UIViewController swizzleMethods:[self class] originalSelector:origSel swizzledSelector:swizSel];
}
 
//exchange implementation of two methods
+ (void)swizzleMethods:(Class)class originalSelector:(SEL)origSel swizzledSelector:(SEL)swizSel
{
    Method origMethod = class_getInstanceMethod(class, origSel);
    Method swizMethod = class_getInstanceMethod(class, swizSel);
     
    //class_addMethod will fail if original method already exists
    BOOL didAddMethod = class_addMethod(class, origSel, method_getImplementation(swizMethod), method_getTypeEncoding(swizMethod));
    if (didAddMethod) {
        class_replaceMethod(class, swizSel, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    } else {
        //origMethod and swizMethod already exist
        method_exchangeImplementations(origMethod, swizMethod);
    }
}
 
- (void)swiz_viewDidAppear:(BOOL)animated
{
    NSLog(@"I am in - [swiz_viewDidAppear:]");
    //handle viewController transistion counting here, before ViewController instance calls its -[viewDidAppear:] method
    //需要注入的代码写在此处
    [self swiz_viewDidAppear:animated];
}
 
@end

如果想统计工程中UIButton的点击事件可以从UIControl的这个方法入手

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- (void)sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event;

第三方库的封装

参考使用Github上的这个库Aspect
Aspect库是对面向切面编程(Aspect Oriented Programming)的实现，里面封装了Runtime的方法，也封装了上文的Method Swizzling方法。
代码如下：

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+ (id<AspectToken>)aspect_hookSelector:(SEL)selector
                      withOptions:(AspectOptions)options
                       usingBlock:(id)block
                            error:(NSError **)error {
    return aspect_add((id)self, selector, options, block, error);
}
 
/// @return A token which allows to later deregister the aspect.
- (id<AspectToken>)aspect_hookSelector:(SEL)selector
                      withOptions:(AspectOptions)options
                       usingBlock:(id)block
                            error:(NSError **)error {
    return aspect_add(self, selector, options, block, error);
}

参考一篇博客的做法，可以把所有埋点操作放到一个类方法中，在程序启动时调用即可

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+ (void)createAllHooks
{
    [UIViewController aspect_hookSelector:@selector(viewDidLoad)
                              withOptions:AspectPositionBefore
                               usingBlock:^(id<AspectInfo> info){
                                   //用户统计代码写在此处
                                   NSLog(@"[ASPECT] inject in class instance:%@", [info instance]);
                               }
                                    error:NULL];
    //other hooks ... goes here
    //...
}