DWURunLoopWorkDistribution源码解读

简介：IOS 合理利用Runloop可高效率利用内存，优化程序性能。DWURunLoopWorkDistribution就是一个合理利用runloop来高效率显示tableview的例子。其不仅包含runloop也包含了runtime的一些内容。

关于runloop主要方法

+(void)_registerRunLoopWorkDistributionAsMainRunloopObserver:(DWURunLoopWorkDistribution *)runLoopWorkDistribution;

static void _registerObserver(CFOptionFlags activities, CFRunLoopObserverRef observer, CFIndex order, CFStringRef mode, void *info, CFRunLoopObserverCallBack callback);

static void _runLoopWorkDistributionCallback(CFRunLoopObserverRef observer, CFRunLoopActivity activity, void *info);

看源码可知道，其实现的是cell图片与label分离，每次当runloop进入休眠状态前进行任务（task）的处理，这样就可合理利用同一线程，节省内存。

具体代码分析

static void _registerObserver(CFOptionFlags activities, CFRunLoopObserverRef observer, CFIndex order, CFStringRef mode, void *info, CFRunLoopObserverCallBack callback) {
    CFRunLoopRef runLoop = CFRunLoopGetCurrent();
    CFRunLoopObserverContext context = {
        0,
        info,
        &CFRetain,
        &CFRelease,
        NULL
    };
    observer = CFRunLoopObserverCreate(     NULL,
                                            activities,
                                            YES,
                                            order,
                                            callback,
                                            &context);
    CFRunLoopAddObserver(runLoop, observer, mode);
    CFRelease(observer);
}

+ (void)_registerRunLoopWorkDistributionAsMainRunloopObserver:(DWURunLoopWorkDistribution *)runLoopWorkDistribution {
    static CFRunLoopObserverRef defaultModeObserver;
    _registerObserver(kCFRunLoopBeforeWaiting, defaultModeObserver, NSIntegerMax - 999, kCFRunLoopDefaultMode, (__bridge void *)runLoopWorkDistribution, &_defaultModeRunLoopWorkDistributionCallback);
}

以默认模式来创建 runloopObserver,其中规定其唤醒条件kCFRunLoopBeforeWaiting即每当线程即将进入休眠状态时便可进行任务的执行。可通过下面方法添加任务

- (void)addTask:(DWURunLoopWorkDistributionUnit)unit withKey:(id)key;

将任务对应的添加到task 和 taskkeys数组数组中方便在注册方法中的callback中以待处理。

以上便是大致思路，关于cell的runtime 处理这里就不再赘述，只把代码附上

@implementation UITableViewCell (DWURunLoopWorkDistribution)

@dynamic currentIndexPath;

- (NSIndexPath *)currentIndexPath {
    NSIndexPath *indexPath = objc_getAssociatedObject(self, @selector(currentIndexPath));
    return indexPath;
}

- (void)setCurrentIndexPath:(NSIndexPath *)currentIndexPath {
    objc_setAssociatedObject(self, @selector(currentIndexPath), currentIndexPath, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end