在Swift中为控制器属性赋值 [英] Assign a value to a controller property in Swift

问题描述

我试图在Swift中的视图之间传递一个int变量，但我不确定如何访问其他View控制器的属性。

I am trying to pass an int variable between views in Swift but I'm not sure how to access the other View controller's property.

在Objective CI中会做类似这样的事情

In Objective C I would do something like this

UIStoryboard *storyBoard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
AnsViewController *ansViewController = [storyBoard instantiateViewControllerWithIdentifier:@"ansView"];
ansViewController.num = theNum;
[self presentViewController:ansViewController animated:YES completion:nil];

在另一个viewcontroller.h文件中我会写这个来声明属性来获取数据

And in the other viewcontroller.h file I would write this to declare the property to get the data

@property (nonatomic) int num;

现在对于Swift我有这个

Now for Swift I have this

let storyBoard : UIStoryboard = UIStoryboard(name: "Main", bundle:nil)
let ansViewController : UIViewController = storyBoard.instantiateViewControllerWithIdentifier("ansView") as UIViewController
ansViewController.num = theNum;
self.presentViewController(ansViewController, animated:true, completion:nil)

and the其他视图控制器的其他.swift文件我通过执行来声明num

and in the other .swift file for the other view controller I declared num by doing

let num: int

我很确定这不是正确的方法，因为我在这一行收到错误

I'm pretty sure that isn't the right way to do it because I get an error on this line

ansViewController.num = theNum;

它说，UIViewController没有名为num的成员我将如何解决此错误，我做错了什么？

and it says, "UIViewController does not have a member named num" How would I resolve this error and what have I done wrong?

谢谢

推荐答案

问题

在Objective C中，你已经明确地将ansViewController定义为AnsViewController *，它具有属性num。

In Objective C, you've explicitly defined ansViewController as an AnsViewController*, which has the property num.

但是，在你的Swift代码中，你已经明确地将ansViewController定义为UIViewController，而不是AnsViewController。因此，编译器不知道这实际上是一个AnsViewController，还是其他一些UIViewController子类，或者只是一个vanilla UIViewController。

In your Swift code, though, you've explicitly defined ansViewController as a UIViewController, not an AnsViewController. So, the compiler has no idea if this is actually an AnsViewController, or some other UIViewController subclass, or just a vanilla UIViewController.

现在解决方案。

我们将尝试将返回的值转发为AnsViewController，然后如果downcast成功则访问该属性（我假设它总是会，但是从你的其余代码和笔尖的上下文中，我不能确定。）

We're going to try to downcast the returned value as an AnsViewController, then access that property if the downcast succeeds (I'm assuming it always will, but out-of-context from the rest of your code and nibs, I can't be sure).

let storyBoard : UIStoryboard = UIStoryboard(name: "Main", bundle:nil)

// To be safe, let's attempt to downcast the returned value as an AnsViewController
if let ansViewController = storyBoard.instantiateViewControllerWithIdentifier("ansView") as? AnsViewController {
    // We get here if the "as?" succeeds with a non-nil value
    ansViewController.num = theNum;
    self.presentViewController(ansViewController, animated:true, completion:nil)
} else {
    // Out of context, I can't see why this case would (or could) ever happen
}

现在，如果你知道这将永远成功（从我所看到的， -instantiateWith的返回值是确定性的，然后你可以更简洁一点：

Now, if you know this will always succeed (from what I can see, the return value of -instantiateWith... is deterministic), then you can be a bit more concise:

let storyBoard : UIStoryboard = UIStoryboard(name: "Main", bundle:nil)

// Force the downcast as an AnsViewController (this could crash at runtime
// if the return value is nil or not an AnsViewController, so again,
// the previous example is safer
let ansViewController = storyBoard.instantiateViewControllerWithIdentifier("ansView") as AnsViewController
ansViewController.num = theNum;
self.presentViewController(ansViewController, animated:true, completion:nil)

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