这是代码：
import Cocoa
@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
@IBOutlet weak var window: NSWindow!
@IBAction func changeBtn(_ sender: NSButton) {
obj1.changeColor()
obj2.changeBackgroundColor()
objFld1.textColor = obj1.color
objFld2.drawsBackground = true
objFld2.backgroundColor = obj2.backgroundColor
}
@IBOutlet weak var objFld1: NSTextField!
@IBOutlet weak var objFld2: NSTextField!
class colored {
var color = NSColor.black
var backgroundColor = NSColor.gray
func changeColor() {
color = NSColor.yellow
}
func changeBackgroundColor() {
backgroundColor = NSColor.blue
}
}
var obj1: colored
var obj2: colored
override init() {
obj1 = colored()
obj2 = colored()
}
func applicationDidFinishLaunching(_ aNotification: Notification) {
// Insert code here to initialize your application
}
func applicationWillTerminate(_ aNotification: Notification) {
// Insert code here to tear down your application
}
}
一切看起来都是无辜的，编译和启动都很好，但是当我点击“更改”按钮时，我得到了一个错误（在调试模式下）：
在发布模式下，错误出现在不同的地方：
知道出了什么问题吗？
macOS Sierra，Xcode 8.1 (8B62)
调试会话给了我这些信息：
InheritProgram`@objc AppDelegate.changeBtn(NSButton) -> ():
0x100001f10 <+0>: pushq %rbp
0x100001f11 <+1>: movq %rsp, %rbp
0x100001f14 <+4>: subq $0x30, %rsp
0x100001f18 <+8>: movq %rdi, -0x8(%rbp)
0x100001f1c <+12>: movq %rdx, %rdi
0x100001f1f <+15>: movq %rsi, -0x10(%rbp)
0x100001f23 <+19>: movq %rdx, -0x18(%rbp)
0x100001f27 <+23>: callq 0x100002bd8 ; symbol stub for: objc_retain
0x100001f2c <+28>: movq -0x8(%rbp), %rdi
0x100001f30 <+32>: movq %rax, -0x20(%rbp)
0x100001f34 <+36>: callq 0x100002bd8 ; symbol stub for: objc_retain
0x100001f39 <+41>: movq -0x18(%rbp), %rdi
0x100001f3d <+45>: movq -0x8(%rbp), %rsi
0x100001f41 <+49>: movq %rax, -0x28(%rbp)
0x100001f45 <+53>: callq 0x100001bd0 ; InheritProgram.AppDelegate.changeBtn (__ObjC.NSButton) -> () at AppDelegate.swift:16
0x100001f4a <+58>: movq -0x8(%rbp), %rdi
0x100001f4e <+62>: callq 0x100002bd2 ; symbol stub for: objc_release
0x100001f53 <+67>: addq $0x30, %rsp
0x100001f57 <+71>: popq %rbp
0x100001f58 <+72>: retq