修改另一个视图控制器swift中的一个变量 [英] Modifing one variable from another view controller swift

问题描述

我正在Swift中开发一个应用程序，用一个主旨，告诉人们各种货币的比特币价格。要选择货币，用户可以从具有UITableView的视图控制器中的列表中进行选择。这是currencyViewController，它是从我的主屏幕viewController呈现的。

I am developing an app in Swift that, in gist, tells people the price of Bitcoin in various currencies. To select the currency, the user chooses from a list in a view controller with a UITableView. This is currencyViewController, and it is presented from my main screen, viewController.

我想要发生的是，当用户解雇currencyViewController时，它将一个字符串传递给一个主视图中的UIButton。

What I want to happen is that, when the user dismisses currencyViewController, it passes a string to a UIButton in the main viewController.

这是应该传递数据的prepareForSegue函数：

Here's the prepareForSegue function that should pass the data:

 override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
    if (segue.identifier == "presentCurrency") {

        currencySelector.setTitle("\currencySelected", forState: UIControlState.Normal)

    }
}

CurrencySelector是主viewController中的UIButton，而currencySelected是第二个视图控制器中的变量currencyViewController。

CurrencySelector is a UIButton in the main viewController, and currencySelected is a variable in the second view controller, currencyViewController.

它给出错误文字中无效的转义序列

It gives the error "Invalid Escape Sequence In Literal"

所以，我把它缩小到两个问题之一：

So, I've narrowed it down to one of two issues:

1. 来自viewCo的变量无法从currencyViewController看到ntroller。如果是这样，我如何从CurrencyViewController修改CurrencySelector的文本？

1. The variables from viewController can't be "seen" from currencyViewController. If so, how can I modify the text of CurrencySelector from CurrencyViewController?

出于某种原因，当用户退出推送的CurrencyViewControler时，不会调用prepareForSegue。

For some reason, when the user exits the pushed CurrencyViewControler, prepareForSegue isn't called.

这里发生了什么？谢谢，道歉 - 我只是一个快速的新手。

What is going on here? Thanks, and apologies - I am but a swift newbie.

推荐答案

2 - 当你推新视图时调用prepareForSegue控制器通过segue，但不是你解雇它。解雇时不会调用segue。

2 - "prepareForSegue" is called when you push a new view controller via the segue, but not when you dismiss it. No segue is called upon dismissal.

1 - 执行此操作的好方法是委托模式。

1 - A good way to do this would be the delegate pattern.

因此主视图控制器将是currencyViewController的委托，并在该控制器被解除时收到消息。

So the main view controller would be the delegate for the currencyViewController, and would receive a message when that controller is dismissed.

在currencyViewController文件的开头，您准备委托：

In the start of the currencyViewController file you prepare the delegate:

protocol CurrencyViewControllerDelegate {
  func currencyViewControllerDidSelect(value: String)
}

并向currencyViewController添加一个变量：

and you add a variable to the currencyViewController:

var delegate : CurrencyViewControllerDelegate?

---

现在，mainViewController必须符合该协议并回答该函数：

---

Now, the mainViewController has to conform to that protocol and answer to that function:

class MainViewController : UIViewController, CurrencyViewControllerDelegate {
  //...  

  func currencyViewControllerDidSelect(value: String)  {
    //do your stuff here
  }
}

一切准备就绪。最后一步，在prepareForSegue（MainViewController）中，您将设置currencyViewController的委托：

And everything is prepared. Last steps, in prepareForSegue (MainViewController), you will set the delegate of the currencyViewController:

var currencyVC = segue.destinationViewController as CurrencyViewController
currencyVC.delegate = self;

当用户选择currencyViewController中的值时，只需在委托中调用该函数：

And when the user selects the value in currencyViewController, just call that function in the delegate:

self.delegate?.currencyViewControllerDidSelect("stuff")

可能有点复杂，但这是一个非常有用的模式:)这里有一个很好的教程，如果你需要更多信息：

A bit complex maybe, but it's a very useful pattern :) here is a nice tutorial with more info if you want it:

http：//www.raywenderlich .com / 75289 / swift-tutorial-part-3-tuples-protocols-delegates-table-views

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