xcode - 非常不寻常的 Xcode 编译行为

Question

自从 Xcode 6.1 和 iOS 8.1 发布以来，我的一个应用程序停止运行了。仅当我使用“发布”而不是“调试”方案在我的设备上“运行”时，我才设法重现该问题。

现在是问题。这在 Debug模式下工作正常:

import Foundation

class CategoryParser {


    var categoriesSettingsDictionary : [String: AnyObject]?


    init() {
        let categoriesURL = NSBundle.mainBundle().URLForResource("CategoriesSettings", withExtension: "plist")
        categoriesSettingsDictionary = NSDictionary(contentsOfURL: categoriesURL!) as? Dictionary<String, AnyObject>
    }
}

但是当我实例化 CategoryParser 类型的对象时，它会在“发布”模式下崩溃。经过多次试验和错误后，我认为要阻止它解决问题，我可以将字典初始化放在两个 println() 语句之间。为什么这些会有什么不同？

import Foundation

class CategoryParser {


    var categoriesSettingsDictionary : [String: AnyObject]?


    init() {
        let categoriesURL = NSBundle.mainBundle().URLForResource("CategoriesSettings", withExtension: "plist")
        println("_")
        categoriesSettingsDictionary = NSDictionary(contentsOfURL: categoriesURL!) as? Dictionary<String, AnyObject>
        println("_")
    }
}

Answer 1

这一定是 Swift 编译器优化方面的错误。我认为，它围绕桥接 NSDictionary至 Dictionary<String,AnyObject> .

我通过以下设置重现了这个问题。

---

环境:Xcode 6.1 (6A1052d)/iPhone 6/iOS 8.1

模板:单 View 应用

CategoriesSettings.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>ct1</key>
    <string>test</string>
</dict>
</plist>

AppDelegate.swift

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        let result = loadPlist()
        println("result: \(result)")
        return true
    }

    func loadPlist() -> [String: AnyObject]? {
        let categoriesURL = NSBundle.mainBundle().URLForResource("CategoriesSettings", withExtension: "plist")
        let dict = NSDictionary(contentsOfURL: categoriesURL!)
        println(dict)
        let result = dict as? [String:AnyObject]
        return result
    }
}

// EOF

输出(使用 -O ):

Optional({
    ct1 = test;
})
result: nil

输出(使用 -Onone ):

Optional({
    ct1 = test;
})
result: Optional(["ct1": test])

---

不过，我不知道最好的解决方法。

也许这行得通:

class CategoryParser {
    var categoriesSettingsDictionary : [String: AnyObject]?
    init() {
        let categoriesURL = NSBundle.mainBundle().URLForResource("CategoriesSettings", withExtension: "plist")
        categoriesSettingsDictionary = NSDictionary(contentsOfURL: categoriesURL!) as? Dictionary<String, AnyObject>
        if categoriesSettingsDictionary == nil {
            // NOTICE: to other developers about this workaround
            println("_")
            println("_")
        }
    }
}

将它们封装在 autoreleasepool 中也有效:

class CategoryParser {
    var categoriesSettingsDictionary : [String: AnyObject]?

    init() {
        autoreleasepool {
            let categoriesURL = NSBundle.mainBundle().URLForResource("CategoriesSettings", withExtension: "plist")
            self.categoriesSettingsDictionary = NSDictionary(contentsOfURL: categoriesURL!) as? Dictionary<String, AnyObject>
        }
    }
}

但是，截至目前，我认为您应该使用 NSDictionary照原样，因为只要你只读它，NSDictionary 之间几乎没有实际区别。和 Dictionary<String,AnyObject>在大多数情况下。

class CategoryParser {
    var categoriesSettingsDictionary : NSDictionary?
    init() {
        let categoriesURL = NSBundle.mainBundle().URLForResource("CategoriesSettings", withExtension: "plist")
        categoriesSettingsDictionary = NSDictionary(contentsOfURL: categoriesURL!)
    }
}

或者，这可能过于激进，但您可以实现自己的 NSDictionary → Dictionary转换器。

extension Dictionary {
    init?(nsDictionaryOrNil:NSDictionary?) {
        if let dict = nsDictionaryOrNil? {
            self = [Key:Value](minimumCapacity: dict.count)
            for (k,v) in dict {
                if let key = k as? Key {
                    if let val = v as? Value {
                        self[key] = val
                        continue
                    }
                }
                return nil
            }
        }
        else {
            return nil
        }
    }
}

class CategoryParser {
    var categoriesSettingsDictionary : [String:AnyObject]?
    init() {
        let categoriesURL = NSBundle.mainBundle().URLForResource("CategoriesSettings", withExtension: "plist")
        let dict = NSDictionary(contentsOfURL: categoriesURL!)
        categoriesSettingsDictionary = [String:AnyObject](nsDictionaryOrNil: dict)
    }
}