在Swift中复制NSTextFieldCell子类会导致崩溃

Question

我一直在尝试创建NSTextFieldCell的子类以与自定义NSTextField（使用Swift）一起使用。但是，在尝试复制子类化单元时，我的代码中断了。我的基本代码是

class XYTextFieldCell: NSTextFieldCell {
    var borderColor = NSColor.init(red: 0.5, green: 0.5, blue: 0.5, alpha: 1)        
    override init(imageCell image: NSImage?) {
        super.init(imageCell: image)
    }

    override init(textCell aString: String) {
        super.init(textCell: aString)
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    deinit {
        Swift.print("Deinit XYTextFieldCell: \(unsafeAddressOf(self))")
    }
}

在AppDelegate中（尝试和模拟小应用程序中的崩溃），我有

func applicationDidFinishLaunching(aNotification: NSNotification) {
    let textFieldCell = XYTextFieldCell.init(textCell: "Test")
    Swift.print("TextFieldCell: \(unsafeAddressOf(textFieldCell))")
    print("textFieldCell.color: \(unsafeAddressOf(textFieldCell.borderColor))")
    copyTextFieldCell(textFieldCell)
}

func copyTextFieldCell(textFieldCell: XYTextFieldCell) {
    Swift.print("TextFieldCell (param): \(unsafeAddressOf(textFieldCell))")
    let copy = textFieldCell.copy() as! XYTextFieldCell
    Swift.print("TextFieldCell (copy): \(unsafeAddressOf(copy))")
    print("copy.color: \(unsafeAddressOf(copy.borderColor))")
}

该应用程序崩溃了

[NSColorSpaceColor release]: message sent to deallocated instance 0x600000075240

全输出是

TextFieldCell: 0x00006080000a61e0 
textFieldCell.color: 0x0000608000074840 
TextFieldCell (param): 0x00006080000a61e0 
TextFieldCell (copy): 0x00006080000a62a0 
copy.color: 0x0000608000074840 
Deinit XYTextFieldCell: 0x00006080000a62a0 
Deinit XYTextFieldCell: 0x00006080000a61e0 
2015-10-09 16:52:35.043 Test[86949:4746488] *** -[NSColorSpaceColor release]: message sent to deallocated instance 0x608000074840

看起来在复制后没有正确保留borderColor（并且正在被双重释放）。然后我尝试添加一个副本重载来尝试强制使用borderColor的副本。

override func copyWithZone(zone: NSZone) -> AnyObject {
        let myCopy = super.copyWithZone(zone) as! XYTextFieldCell
        myCopy.borderColor = borderColor.copyWithZone(zone) as! NSColor

        return myCopy
    }

但是，它仍然会因同样的错误而崩溃

TextFieldCell: 0x00006080000ab4c0 textFieldCell.color: 0x00006080000769c0    
TextFieldCell (param): 0x00006080000ab4c0 
TextFieldCell (copy): 0x00006080000ab520 
copy.color: 0x00006080000769c0 
Deinit XYTextFieldCell: 0x00006080000ab520 
Deinit XYTextFieldCell: 0x00006080000ab4c0 
2015-10-09 16:54:54.248 Test[87031:4749016] *** -[NSColorSpaceColor release]: message sent to deallocated instance 0x6080000769c0

我可以通过在copyWithZone中执行新的XYTextFieldCell来避免崩溃:(而不是调用super.copyWithZone）。但是，这意味着我必须手动将所有超类定义的属性重新分配给我的副本。

有没有办法正确地复制NSTextFieldCell，这样它就不会双重释放我的子类属性。我也注意到从NSButtonCell继承子类时的这种行为。但是，如果我不从任何一个继承（XYTextFieldCell是根Swift类），那么它工作正常。谢谢

Answer 1

我知道这是一个老问题，但我想我会回答它。您需要为复制的对象添加保留。以下是我为可选的NSColor做的方法：

class TableViewTextFieldCell: NSTextFieldCell {

    private var previousTextColor: NSColor?

    // Super newbie mistake of forgetting to implement copyWithZone; why would we need it if we aren't using a cell-based NSTableView?  This shouldn't be needed..but apparently NSTextFieldCell's baseline measurement with autolayout does a copy! who would have guessed. NSCell's implementation does a NSCopyObject, which doesn't retain ivars
    override func copy(with zone: NSZone? = nil) -> Any {
        let result: TableViewTextFieldCell = super .copy(with: zone) as! TableViewTextFieldCell
        if let previousTextColor = result.previousTextColor {
            // Add the needed retain now
            let _ = Unmanaged<NSColor>.passRetained(previousTextColor)
        }
        return result
    }
}

Answer 2

看起来我被NSCopyObject（）捕获为详细的here。链接的要点是NSCell子类使用NSCopyObject（）符合NSCopying协议 - 而NSCopyObject（）似乎没有正确设置保留计数。

在那里概述的解决方案是在Objective-C中，我不知道如何将其转换为Swift（因为它涉及直接访问copyWithZone：方法中的Objective-C ivars）。所以，我必须在objective-c中实现基本子类（并在objective-c中执行复制）。然后我将它桥接到一个快速的子类

RMTextFieldCell.h（在objective-c中）

#import <Cocoa/Cocoa.h>

@interface RMTextFieldCell : NSTextFieldCell

@property (nonatomic, strong) NSColor* borderColor;

@end

RMTextFieldCell.m（在objective-c中）

#import "RMTextFieldCell.h"

@implementation RMTextFieldCell

-(id) initTextCell:(NSString *)aString
{
    self = [super initTextCell:aString];
    [self setup];

    return self;
}

-(id) initImageCell:(NSImage *)image
{
    self = [super initImageCell:image];
    [self setup];

    return self;
}

-(id) initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];
    [self setup];

    return self;
}

-(RMTextFieldCell*) copyWithZone:(NSZone*) zone
{
    RMTextFieldCell* copy = [super copyWithZone:zone];
    copy->_borderColor = nil;
    copy.borderColor = self.borderColor;

    return copy;
}

-(void) setup
{
    self.borderColor = [NSColor colorWithRed:0.5 green:0.5 blue:0.5 alpha:1.0];
}

@end

RMSwiftTextFieldCell.swift（在swift中）

import Cocoa

class RMSwiftTextFieldCell: RMTextFieldCell {


    override init(imageCell image: NSImage?) {
        super.init(imageCell: image)
    }

    override init(textCell aString: String) {
        super.init(textCell: aString)
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    deinit {
        Swift.print("Deinit RMTextFieldCell: \(unsafeAddressOf(self))")
    }
}

这有点令人费解，但似乎在我的初步测试中起作用。如果有人有更好的解决方案，我将不胜感激:)谢谢

编辑：看起来我甚至不需要在objective-c子类中实现copyWithZone：