swift 多线程的使用

public func asyncAfter(deadline: DispatchTime, qos: DispatchQoS = default, flags: DispatchWorkItemFlags = default, execute work: @escaping @convention(block) () -> Swift.Void)

public func asyncAfter(wallDeadline: DispatchWallTime, qos: DispatchQoS = default, flags: DispatchWorkItemFlags = default, execute work: @escaping @convention(block) () -> Swift.Void)

public func asyncAfter(deadline: DispatchTime, execute: DispatchWorkItem)

public func asyncAfter(wallDeadline: DispatchWallTime, execute: DispatchWorkItem)

public func asyncAfter(deadline: DispatchTime, execute: DispatchWorkItem)
// 该方法接收一个DispatchTime的参数,点进这个类型的里面可以发现实个结构体
public struct DispatchTime : Comparable {
public let rawValue: dispatch_time_t
public static func now() -> DispatchTime
public static let distantFuture: DispatchTime
public init(uptimeNanoseconds: UInt64)
public var uptimeNanoseconds: UInt64 { get }
}
//
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 2, execute: {
self.tableView?.reloadData()
if self.refreshControl?.isRefreshing == true {
self.refreshControl?.endRefreshing()
}
})

DispatchTime.now() 获取当前时间,
DispatchTime.now() + 2, 在当前时间的基础上加2,那就是延时两秒了