switch-statement - switch 语句出错了 - swift 语言

Question

在 Obj-c 中，我做了一个 switch 语句，我曾经使用 UIsplitviewcontroller 在我的 iPad 应用程序中四处移动现在我想快速地做同样的事情……我试了几个小时，现在我唯一没能尝试的是代码，因为它说了某种编译错误反正这是我在 Obj-c 中得到的

-(void)initialSite:(int)viewId {
UIViewController *viewController;
switch (viewId) {
    case 0:{
        viewController = self.initital;
        NSString *star = [NSString stringWithFormat:@"Velkommen til %@'s  Bog",[data valueForKey:@"navn"]];
        self.navigationItem.title = star;}
        break;
    case 1:{
        viewController = self.startSide;
        NSString *start = [NSString stringWithFormat:@"%@'s  Bog, start-side",[data valueForKey:@"navn"]];
        self.navigationItem.title = start;}
        break;
}
[self showChildViewController:viewController];

}

这是我到目前为止在 swift 中得出的结论。对此仍然很陌生，即使我有快速编程语言书，理解它也有点困难

这是我到目前为止在 swift 中得到的结果

    let viewController = UIViewController()
switch viewController {
case "initial":
let initial : UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
let vc0 : UIViewController = initial.instantiateViewControllerWithIdentifier("initial") as UIViewController
self.presentViewController(vc0, animated: true, completion: nil)
let rowData: NSDictionary = self.menuItemArray[indexPath.row] as NSDictionary!
self.navigation.title = rowData["navn"] as? String

case "startSide":
let startSide : UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
let vc1 : UIViewController = startSide.instantiateViewControllerWithIdentifier("startSide") as UIViewController
let rowData: NSDictionary = self.manuItemArray[indexPath.row] as NSDictionary!
self.presentViewController(vc1, animated: true, completion: nil)
self.navigation.title = rowData["navn"] as? String
default:


}

错误是:Expected declaration at the line with 让 viewController = UIViewcontroller()

Answer 1

让我们从您的 Obj-C 实现开始:

-(void)initialSite:(int)viewId 
{
    UIViewController *viewController;
    switch (viewId) 
    {
        case 0:
        {
            viewController = self.initital;
            NSString *star = [NSString stringWithFormat:@"Velkommen til %@'s  Bog",[data valueForKey:@"navn"]];
            self.navigationItem.title = star;
        }
        break;
        case 1:
        {
            viewController = self.startSide;
            NSString *start = [NSString stringWithFormat:@"%@'s  Bog, start-side",[data valueForKey:@"navn"]];
            self.navigationItem.title = start;
        }
        break;
    }

    [self showChildViewController:viewController];
}

现在 Swift 中的相同片段:

func initialSite(viewID:Int)
{
    var viewController : UIViewController?

    switch (viewID)
    {
        case 0:
            viewController = self.initial
            let navn = self.data["navn"] as? String
            let star = "Velkommen til \(navn)'s Bog"
            self.navigationItem.title = star

        case 1:
            viewController = self.startSide
            let navn = self.data["navn"] as? String
            let star = "\(navn)'s Bog, start-side"
            self.navigationItem.title = star

        default:
            viewController = nil
            // do nothing
    }

    self.showChildViewController(viewController)
}

您必须记住的主要事情是 var 与 let 的区别。通常，您将使用 let 来创建事物，除非这些事物稍后会更改其值，您可以使用 var。

另一件事是可选值的使用，带有 ? 后缀。这是当值可能为 nil(未设置)时，否则它必须包含一个值。