有两种常见的模式，这两种模式都消除了viewController2明确了解viewController1的需要（这对于可维护性非常重要）：

1. 为您的viewController2创建委托协议，并将viewController1设置为委托。每当您想将数据发送回viewController1时，都要使viewController2将数据“委托”

2. 将闭包设置为允许传递数据的属性。当显示viewController2时，viewController1将在viewController2上实现该关闭。每当viewController2有数据要传回时，它将调用闭包。我觉得这种方法更“迅捷”。

这是＃2的一些示例代码：

class ViewController2 : UIViewController {
    var onDataAvailable : ((data: String) -> ())?

    func sendData(data: String) {
        // Whenever you want to send data back to viewController1, check
        // if the closure is implemented and then call it if it is
        self.onDataAvailable?(data: data)
    }
}

class ViewController1 : UIViewController {
   func doSomethingWithData(data: String) {
        // Do something with data
    }
    override func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
        // When preparing for the segue, have viewController1 provide a closure for
        // onDataAvailable
        if let viewController = segue.destinationViewController as? ViewController2 {
            viewController.onDataAvailable = {[weak self]
                (data) in
                if let weakSelf = self {
                    weakSelf.doSomethingWithData(data)
                }
            }
        }
    }
}