建筑成功然后弹出"Thread 1: signal SIGABRT error"

Question

我正在初步构建计算器。目前，代码只是在用户点击时将数字和 Pi 打印到计算器的标签中。

1)车码

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var display: UILabel! = nil

    var userIsInTheMiddleOfTypeing = false

    @IBAction func touchDigit(_ sender: UIButton){
        let digit = sender.currentTitle!
        if userIsInTheMiddleOfTypeing {
            let textCurrentlyInDisplay = display.text!
            display.text = textCurrentlyInDisplay + digit
        } else {
            display.text = digit
        }

        userIsInTheMiddleOfTypeing = true
    }

    @IBAction func performOperation(_ sender: UIButton) {
        userIsInTheMiddleOfTypeing = false
        if let methematicalSymbol = sender.currentTitle {
            if methematicalSymbol == "π" {
                display.text = String(M_PI) // M_PI
            }
        }
    }      
}

2) UI

touchDigit函数链接到所有数字按钮，如下图所示。 display 是 UILable 而 performOperaton 是 PI 按钮

问题

当我构建代码时，Xcode首先告诉我构建成功，但是，在我做任何事情之前，弹出如下错误

错误日志（从调试区复制）

2016-07-28 19:30:30.215343 Calculator[11671:208157] bundleid: com.Jeffery.Calculator, enable_level: 0, persist_level: 0, propagate_with_activity: 0
2016-07-28 19:30:30.218796 Calculator[11671:208157] Created DB, header sequence number = 260
2016-07-28 19:30:30.767300 Calculator[11671:208178] subsystem: com.apple.UIKit, category: HIDEvents, enable_level: 0, persist_level: 0, default_ttl: 0, info_ttl: 0, debug_ttl: 0, generate_symptoms: 0, enable_oversize: 0, privacy_setting: 0
2016-07-28 19:30:31.022078 Calculator[11671:208157] Created DB, header sequence number = 260
2016-07-28 19:30:31.350380 Calculator[11671:208157] subsystem: com.apple.BaseBoard, category: MachPort, enable_level: 0, persist_level: 0, default_ttl: 0, info_ttl: 0, debug_ttl: 0, generate_symptoms: 0, enable_oversize: 0, privacy_setting: 0
2016-07-28 19:30:31.388363 Calculator[11671:208159] subsystem: com.apple.FrontBoard, category: Common, enable_level: 0, persist_level: 0, default_ttl: 0, info_ttl: 0, debug_ttl: 0, generate_symptoms: 0, enable_oversize: 0, privacy_setting: 0
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)

Answer 1

我认为这里有问题：'@IBOutlet 弱变量显示：UILabel！ = 零'。当你用 'display' 属性做某事时，你尝试用 nil 做。在声明属性后尝试删除 '= nil'。或者你可以覆盖视图控制器初始化方法，但对我来说，在这种情况下这是不好的方法。

Answer 2

我弄清楚了我的错误，PI 按钮有两个连接到 viewControler（我应该删除一个）。

建筑成功然后弹出"Thread 1: signal SIGABRT error"

Building success then "Thread 1: signal SIGABRT error" pops up

ios

swift3

xcode8-beta3