將委託分配給嵌套範圍中的NSOpenPanel原因EXC_BAD_ACCESS

請考慮以下簡化的代碼示例。它在Swift中介紹，但在Objective-C中發生相同的行爲。將委託分配給嵌套範圍中的NSOpenPanel原因EXC_BAD_ACCESS

import Foundation 
import Cocoa 
class MainWindow : NSWindow { 
    @IBAction func onClick_openFile(sender : AnyObject?) { 
     let path = runOpenPanel(false); 
     NSLog(path as String) 
    } 

    @IBAction func onClick_crashyByeBye(sender : AnyObject?) { 
     let path = runOpenPanel(true); 
     NSLog(path as String) 
    } 

    private func runOpenPanel(useCrashyDelegate : Bool) -> NSString { 
     let openPanel = NSOpenPanel.init() 
     openPanel.canChooseDirectories = false 
     openPanel.canChooseFiles = true 
     openPanel.allowsMultipleSelection = false 

     let safeDelegate = MyOpenPanelDelegate.init() //same scope as openPanel.runModal()--works fine 
     if (useCrashyDelegate) { 
      let crashyDelegate = MyOpenPanelDelegate.init() //falls out of scope before openPanel.runModal() and crashes 
      openPanel.delegate = crashyDelegate 
     } else { 
      openPanel.delegate = safeDelegate 
     } 

     if (openPanel.runModal() == NSFileHandlingPanelOKButton && openPanel.URLs.count == 1) { 
      return openPanel.URLs[0].path! 
     } 

     return "" 
    } 
} 

class MyOpenPanelDelegate : NSObject, NSOpenSavePanelDelegate { 
    func panel(sender: AnyObject, shouldEnableURL url: NSURL) -> Bool { 
     var isDir : ObjCBool = false 
     if (NSFileManager.defaultManager().fileExistsAtPath(url.path!, isDirectory: &isDir)) { 
      return isDir || (url.path! as NSString).lastPathComponent.lowercaseString == "foo.txt" 
     } 
     return false 
    } 
}

當useCrashyDelegate參數runOpenPanel是真實的，crashyDelegate在嵌套範圍被實例化並調用openPanel.runModal()之前超出範圍。由於打開的面板將crashyDelegate分配給它的委託，我期望crashyDelegate's引用計數增加。但是，當useCrashyDelegate爲真時，應用程序會崩潰EXC_BAD_ACCESS。如果useCrashyDelegate爲假，則在與調用openPanel.runModal()相同範圍內實例化的safeDelegate被分配給打開的面板，並且沒有EXC_BAD_ACCESS。

這讓我相信NSOpen P anel不會遞增其委託的引用計數。這是預期的行爲，還是這可能是一個錯誤？

來源

2016-04-13 Outdoor Ed

這讓我相信NSOpenPanel不會遞增其委託的引用計數。這是預期的行爲，還是這可能是一個錯誤？

它是預期的。檢查屬性的類型，你會看到它是assign（Objective-C）或unsafe（Swift），不保留強烈的參考。這是可可代表的常見設計模式。

HTH

來源

2016-04-13 05:10:39 CRD

將委託分配給嵌套範圍中的NSOpenPanel原因EXC_BAD_ACCESS

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