在Swift中调用getter方法时崩溃
在Swift中调用getter方法时崩溃
提问于 2015-06-16 00:59:14
我正在iTunes U上上斯坦福大学的iOS课程，在调用getter方法时出现了奇怪的行为
import UIKit
class ViewController: UIViewController {
@IBOutlet weak var display: UILabel!
var newNumber = true
var operandStack = Array<Double>()
var displayValue: Double{
get{
return NSNumberFormatter().numberFromString(display.text!)!.doubleValue
}
set{
display.text = "\(newNumber)"
newNumber = true
}
}
@IBAction func appendDigit(sender: UIButton) {
let digit = sender.currentTitle!
if(newNumber){
display.text = digit
newNumber = false
}else{
display.text = display.text! + digit
}
}
@IBAction func enter() {
if(!newNumber){
newNumber = true
}
operandStack.append(displayValue)
println("\(operandStack)")
}
}当调用enter()方法时，我得到了一个崩溃，其中的断点指向displayValue get方法中的返回语句。如果我忽略get方法并调用
operandStack.append(NSNumberFormatter().numberFromString(display.text!)!.doubleValue)一切正常，但我不明白为什么get方法会崩溃，它不是做了与上面的代码完全相同的事情吗？
这是完整的回溯
* thread #1: tid = 0x133463, 0x000e4738 Kalkylator`Kalkylator.ViewController.displayValue.getter : Swift.Double(self=0x7986d560) + 24 at ViewController.swift:17, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
* frame #0: 0x000e4738 Kalkylator`Kalkylator.ViewController.displayValue.getter : Swift.Double(self=0x7986d560) + 24 at ViewController.swift:17
frame #1: 0x000e57c2 Kalkylator`Kalkylator.ViewController.enter (self=0x7986d560)() -> () + 130 at ViewController.swift:39
frame #2: 0x000e5992 Kalkylator`@objc Kalkylator.ViewController.enter (Kalkylator.ViewController)() -> () + 34 at ViewController.swift:0
frame #3: 0x01d0c7cd libobjc.A.dylib`-[NSObject performSelector:withObject:withObject:] + 84
frame #4: 0x00b1aa90 UIKit`-[UIApplication sendAction:to:from:forEvent:] + 99
frame #5: 0x00b1aa22 UIKit`-[UIApplication sendAction:toTarget:fromSender:forEvent:] + 64
frame #6: 0x00c5b18a UIKit`-[UIControl sendAction:to:forEvent:] + 69
frame #7: 0x00c5b5a7 UIKit`-[UIControl _sendActionsForEvents:withEvent:] + 598
frame #8: 0x00c5a811 UIKit`-[UIControl touchesEnded:withEvent:] + 660
frame #9: 0x00b72cfa UIKit`-[UIWindow _sendTouchesForEvent:] + 874
frame #10: 0x00b737d6 UIKit`-[UIWindow sendEvent:] + 792
frame #11: 0x00b316d1 UIKit`-[UIApplication sendEvent:] + 242
frame #12: 0x00b41b08 UIKit`_UIApplicationHandleEventFromQueueEvent + 21484
frame #13: 0x00b15337 UIKit`_UIApplicationHandleEventQueue + 2300
frame #14: 0x0021706f CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
frame #15: 0x0020cb7d CoreFoundation`__CFRunLoopDoSources0 + 253
frame #16: 0x0020c0d8 CoreFoundation`__CFRunLoopRun + 952
frame #17: 0x0020ba5b CoreFoundation`CFRunLoopRunSpecific + 443
frame #18: 0x0020b88b CoreFoundation`CFRunLoopRunInMode + 123
frame #19: 0x03fa32c9 GraphicsServices`GSEventRunModal + 192
frame #20: 0x03fa3106 GraphicsServices`GSEventRun + 104
frame #21: 0x00b19106 UIKit`UIApplicationMain + 1526
frame #22: 0x000eec64 Kalkylator`main + 180 at AppDelegate.swift:12
frame #23: 0x02407ac9 libdyld.dylib`start + 1回答 3
Stack Overflow用户
发布于 2015-06-16 01:06:03
var newNumber = true这是一个布尔值。
display.text = "\(newNumber)"您正在将标注的文本设置为该布尔值
NSNumberFormatter().numberFromString(display.text在这里，您是从布尔值创建数字，而不是从NSNumber。
你的意思可能是"newValue“。
Stack Overflow用户
发布于 2015-06-16 02:37:01
以下是修改后的工作代码：
你得到崩溃的那条线已经被替换了。
import UIKit
class ViewController: UIViewController {
@IBOutlet weak var display: UILabel!
var newNumber = true
var operandStack = Array<Double>()
var displayValue: Double {
get{
return (display.text! as NSString).doubleValue // Changed Line
}
set{
display.text = "\(newNumber)"
newNumber = true
}
}
@IBAction func appendDigit(sender: UIButton) {
let digit = sender.currentTitle!
if(newNumber){
display.text = digit
newNumber = false
}else{
display.text = display.text! + digit
}
}
@IBAction func enter() {
if(!newNumber){
newNumber = true
}
operandStack.append(displayValue)
println("\(operandStack)")
}
}Stack Overflow用户
发布于 2015-06-19 17:51:57
事实证明我只是意外地放置了一个断点，而不知道它是什么。去掉它当然就解决了问题
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/30850835
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