顶层不允许使用表达式

Question

我是 Swift 初学者。

以下代码似乎在 Xcode 7.0 Playground 中编译得很好（没有可见的错误）：

//: Playground - noun: a place where people can play

//#!/usr/bin/env xcrun swift

import WebKit

let application = NSApplication.sharedApplication()
application.setActivationPolicy(NSApplicationActivationPolicy.Regular)
let window = NSWindow()
window.setContentSize(NSSize(width:800, height:600))
window.styleMask = NSTitledWindowMask | NSClosableWindowMask | NSMiniaturizableWindowMask
window.center()
window.title = "Minimal Swift WebKit Browser"
window.makeKeyAndOrderFront(window)

class WindowDelegate: NSObject, NSWindowDelegate {

    func windowWillClose(notification: NSNotification) {
        NSApplication.sharedApplication().terminate(0)
    }
}
let windowDelegate = WindowDelegate()
window.delegate = windowDelegate

class ApplicationDelegate: NSObject, NSApplicationDelegate {
    var _window: NSWindow

    init(window: NSWindow) {
        self._window = window
    }

    func applicationDidFinishLaunching(notification: NSNotification) {
        let webView = WebView(frame: self._window.contentView!.frame)
        self._window.contentView!.addSubview(webView)
        webView.mainFrame.loadRequest(NSURLRequest(URL: NSURL(string: "http://www.apple.com")!))
    }
}

将完全相同的代码粘贴到 OSX 的新 Cocoa 应用程序的“AppDelegate.swift”文件中时，出现 7 个错误，完全相同：“表达式不允许在顶层”。

通过搜索，我推断 Playground 允许正常项目不允许的事情，并且由于表达式“在类或实例方法之外”而发生错误。

但是我不确定如何修改程序才能正确构建。

Answer 1

是的，普通项目不允许顶层代码，因为它没有明显的运行时间。您需要决定何时应该运行您的激活策略和窗口/委托代码（即，将该代码移动到方法中）。我建议applicationDidFinishLaunching(_:)，因为它在您的应用程序完成启动时调用，并且是进行此类设置的常见位置。完成后的代码如下：

import WebKit

class WindowDelegate: NSObject, NSWindowDelegate {
    func windowWillClose(notification: NSNotification) {
        NSApplication.sharedApplication().terminate(0)
    }
}

class ApplicationDelegate: NSObject, NSApplicationDelegate {
    var _window: NSWindow

    init(window: NSWindow) {
        self._window = window
    }

    func applicationDidFinishLaunching(notification: NSNotification) {
        let webView = WebView(frame: self._window.contentView!.frame)
        self._window.contentView!.addSubview(webView)
        webView.mainFrame.loadRequest(NSURLRequest(URL: NSURL(string: "http://www.apple.com")!))

        let application = NSApplication.sharedApplication()
        application.setActivationPolicy(NSApplicationActivationPolicy.Regular)
        let window = NSWindow()
        window.setContentSize(NSSize(width:800, height:600))
        window.styleMask = NSTitledWindowMask | NSClosableWindowMask | NSMiniaturizableWindowMask
        window.center()
        window.title = "Minimal Swift WebKit Browser"
        window.makeKeyAndOrderFront(window)

        let windowDelegate = WindowDelegate()
        window.delegate = windowDelegate
    }
}