Swift Dispatch After的实现

OC中

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.25 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        if (complete) {
            complete();
        }
    });

Swift中

let delayTime = DispatchTime.now() + DispatchTimeInterval.seconds(3)
        DispatchQueue.global().asyncAfter(deadline: delayTime) {
            complete?()
        }