xcode - PrepareForSegue 有效，但访问目标的变量会使应用程序崩溃

Question

我正在尝试在方法 prepareForSegue 中设置标签的文本组件，但应用程序在执行该方法时崩溃，我查看了其他讨论，但没有一个对我有帮助，我正在快速编程最新版本的 xCode 和构建到 iPhone。当我删除将标签文本设置为“Meal name”的行时，不会发生崩溃。断点位于设置标签文本的行上。如果有人能帮助我，那就太好了，谢谢。

-- 编辑--

prepareForSegue FirstViewController 代码:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    let dest : SecondViewController = segue.destinationViewController as! SecondViewController
    dest.mealNameLabel.text = "Meal Name"
}

完整堆栈跟踪:(-> 是中断)

    libswiftCore.dylib`function signature specialization <Arg[0] = Exploded, Arg[1] = Exploded, Arg[2] = Dead, Arg[3] = Dead> of Swift._fatalErrorMessage (Swift.StaticString, Swift.StaticString, Swift.StaticString, Swift.UInt) -> ():
    0x1001de55c <+0>:   stp    x29, x30, [sp, #-16]!
    0x1001de560 <+4>:   mov    x29, sp
    0x1001de564 <+8>:   sub    sp, sp, #16               ; =16 
    0x1001de568 <+12>:  and    w8, w2, #0x1
    0x1001de56c <+16>:  tbnz   w8, #0, 0x1001de58c       ; <+48>
    0x1001de570 <+20>:  tbnz   x1, #63, 0x1001de5c8      ; <+108>
    0x1001de574 <+24>:  add    x1, x0, x1
    0x1001de578 <+28>:  mov    x2, x3
    0x1001de57c <+32>:  mov    x3, x4
    0x1001de580 <+36>:  mov    x4, x5
    0x1001de584 <+40>:  bl     0x1002265b0               ; function signature specialization <Arg[0] = Exploded, Arg[1] = Exploded> of Swift.(_fatalErrorMessage (Swift.StaticString, Swift.StaticString, Swift.StaticString, Swift.UInt) -> ()).(closure #2)

->  0x1001de588 <+44>:  brk    #0x1
    0x1001de58c <+48>:  str    xzr, [sp, #8]
    0x1001de590 <+52>:  cmp    x0, w0, uxtw
    0x1001de594 <+56>:  b.ne   0x1001de6e0               ; <+388>
    0x1001de598 <+60>:  lsr    w8, w0, #11
    0x1001de59c <+64>:  cmp    w8, #26                   ; =26 
    0x1001de5a0 <+68>:  b.hi   0x1001de5ec               ; <+144>
    0x1001de5a4 <+72>:  cmp    w0, #128                  ; =128 
    0x1001de5a8 <+76>:  b.lo   0x1001de630               ; <+212>
    0x1001de5ac <+80>:  cmp    w0, #2048                 ; =2048 
    0x1001de5b0 <+84>:  b.hs   0x1001de660               ; <+260>
    0x1001de5b4 <+88>:  movz   x8, #0
    0x1001de5b8 <+92>:  movz   x10, #0
    0x1001de5bc <+96>:  lsr    w9, w0, #6
    0x1001de5c0 <+100>: orr    w9, w9, #0xffffffc0
    0x1001de5c4 <+104>: b      0x1001de694               ; <+312>
    0x1001de5c8 <+108>: adr    x0, #723338               ; "fatal error"
    0x1001de5cc <+112>: nop    
    0x1001de5d0 <+116>: adr    x3, #723840               ; "UnsafeBufferPointer with negative count"
    0x1001de5d4 <+120>: nop    
    0x1001de5d8 <+124>: movz   w1, #0xb
    0x1001de5dc <+128>: orr    w2, wzr, #0x2
    0x1001de5e0 <+132>: movz   w4, #0x27
    0x1001de5e4 <+136>: orr    w5, wzr, #0x2
    0x1001de5e8 <+140>: bl     0x1001de55c               ; <+0>
    0x1001de5ec <+144>: cmp    w0, #14, lsl #12          ; =57344 
    0x1001de5f0 <+148>: b.lo   0x1001de63c               ; <+224>
    0x1001de5f4 <+152>: cmp    w0, #272, lsl #12         ; =1114112 
    0x1001de5f8 <+156>: b.hs   0x1001de738               ; <+476>
    0x1001de5fc <+160>: lsr    w8, w0, #6
    0x1001de600 <+164>: lsr    w9, w0, #16
    0x1001de604 <+168>: cbz    w9, 0x1001de664           ; <+264>
    0x1001de608 <+172>: lsr    w9, w0, #18
    0x1001de60c <+176>: orr    w9, w9, #0xf0
    0x1001de610 <+180>: cmp    w9, w9, uxtb
    0x1001de614 <+184>: b.ne   0x1001de6e0               ; <+388>
    0x1001de618 <+188>: orr    w10, wzr, #0xffffff80
    0x1001de61c <+192>: bfxil  w10, w0, #12, #6
    0x1001de620 <+196>: and    x12, x9, #0xff
    0x1001de624 <+200>: str    x12, [sp, #8]
    0x1001de628 <+204>: orr    w11, wzr, #0x1
    0x1001de62c <+208>: b      0x1001de674               ; <+280>
    0x1001de630 <+212>: movz   x8, #0
    0x1001de634 <+216>: movz   x9, #0
    0x1001de638 <+220>: b      0x1001de6d0               ; <+372>
    0x1001de63c <+224>: adr    x0, #723222               ; "fatal error"
    0x1001de640 <+228>: nop    
    0x1001de644 <+232>: adr    x3, #726652               ; "high- and low-surrogate code points are not valid Unicode scalar values"
    0x1001de648 <+236>: nop    
    0x1001de64c <+240>: movz   w1, #0xb
    0x1001de650 <+244>: orr    w2, wzr, #0x2
    0x1001de654 <+248>: movz   w4, #0x47
    0x1001de658 <+252>: orr    w5, wzr, #0x2
    0x1001de65c <+256>: bl     0x1001de55c               ; <+0>
    0x1001de660 <+260>: lsr    w8, w0, #6
    0x1001de664 <+264>: lsr    w9, w0, #12
    0x1001de668 <+268>: movz   x11, #0
    0x1001de66c <+272>: movz   x12, #0
    0x1001de670 <+276>: orr    w10, w9, #0xffffffe0
    0x1001de674 <+280>: lsl    x13, x11, #3
    0x1001de678 <+284>: orr    w9, wzr, #0xffffff80
    0x1001de67c <+288>: bfxil  w9, w8, #0, #6
    0x1001de680 <+292>: and    w8, w10, #0xff
    0x1001de684 <+296>: lsl    x8, x8, x13
    0x1001de688 <+300>: orr    x10, x8, x12
    0x1001de68c <+304>: str    x10, [sp, #8]
    0x1001de690 <+308>: add    x8, x11, #1               ; =1 
    0x1001de694 <+312>: orr    w11, wzr, #0x8
    0x1001de698 <+316>: umulh  x11, x8, x11
    0x1001de69c <+320>: cmp    xzr, x11
    0x1001de6a0 <+324>: b.ne   0x1001de6e0               ; <+388>
    0x1001de6a4 <+328>: lsl    x11, x8, #3
    0x1001de6a8 <+332>: cmp    x11, #63                  ; =63 
    0x1001de6ac <+336>: b.hi   0x1001de714               ; <+440>
    0x1001de6b0 <+340>: orr    w12, wzr, #0x80
    0x1001de6b4 <+344>: bfxil  x12, x0, #0, #6
    0x1001de6b8 <+348>: and    w9, w9, #0xff
    0x1001de6bc <+352>: lsl    x9, x9, x11
    0x1001de6c0 <+356>: orr    x9, x9, x10
    0x1001de6c4 <+360>: str    x9, [sp, #8]
    0x1001de6c8 <+364>: add    x8, x8, #1                ; =1 
    0x1001de6cc <+368>: mov    x0, x12
    0x1001de6d0 <+372>: orr    w10, wzr, #0x8
    0x1001de6d4 <+376>: umulh  x10, x8, x10
    0x1001de6d8 <+380>: cmp    xzr, x10
    0x1001de6dc <+384>: b.eq   0x1001de6e4               ; <+392>
    0x1001de6e0 <+388>: brk    #0x1
    0x1001de6e4 <+392>: lsl    x10, x8, #3
    0x1001de6e8 <+396>: cmp    x10, #64                  ; =64 
    0x1001de6ec <+400>: b.hs   0x1001de714               ; <+440>
    0x1001de6f0 <+404>: and    x11, x0, #0xff
    0x1001de6f4 <+408>: lsl    x10, x11, x10
    0x1001de6f8 <+412>: orr    x9, x10, x9
    0x1001de6fc <+416>: str    x9, [sp, #8]
    0x1001de700 <+420>: add    x9, sp, #8                ; =8 
    0x1001de704 <+424>: add    x8, x8, x9
    0x1001de708 <+428>: add    x1, x8, #1                ; =1 
    0x1001de70c <+432>: add    x0, sp, #8                ; =8 
    0x1001de710 <+436>: b      0x1001de578               ; <+28>
    0x1001de714 <+440>: adr    x0, #723006               ; "fatal error"
    0x1001de718 <+444>: nop    
    0x1001de71c <+448>: adr    x3, #723412               ; "shift amount is larger than type size in bits"
    0x1001de720 <+452>: nop    
    0x1001de724 <+456>: movz   w1, #0xb
    0x1001de728 <+460>: orr    w2, wzr, #0x2
    0x1001de72c <+464>: movz   w4, #0x2d
    0x1001de730 <+468>: orr    w5, wzr, #0x2
    0x1001de734 <+472>: bl     0x1001de55c               ; <+0>
    0x1001de738 <+476>: adr    x0, #722970               ; "fatal error"
    0x1001de73c <+480>: nop    
    0x1001de740 <+484>: adr    x3, #726480               ; "value is outside of Unicode codespace"
    0x1001de744 <+488>: nop    
    0x1001de748 <+492>: movz   w1, #0xb
    0x1001de74c <+496>: orr    w2, wzr, #0x2
    0x1001de750 <+500>: movz   w4, #0x25
    0x1001de754 <+504>: orr    w5, wzr, #0x2
    0x1001de758 <+508>: bl     0x1001de55c               ; <+0>

这是我使用 dest 访问的 View Controller 的代码:(感谢 Emptyless)

//
//  SecondViewController.swift
//  FoodTracker
//
//  Created by Michael Buerger on 7/4/16.
//  Copyright © 2016 Michael Buerger. All rights reserved.
//

import UIKit

class SecondViewController: UIViewController {

    // MARK: Properties
    @IBOutlet weak var mealNameLabel: UILabel!
    var mealName: String?

    override func viewDidLoad() {
        super.viewDidLoad()
        if mealName != nil {
            mealNameLabel.text = mealName
        }

    }
}

Answer 1

问题很可能是您正在访问尚未初始化的 IBOutlet。如果不是直接设置 UITextLabel，而是创建一个保存文本的变量，您可能会更幸运:

作为 SecondViewController 的属性:

var labelText : String?

在 FirstViewController 的 prepareForSegue() 中:

des.labelText = "Your Text"

在 SeconViewController 的 viewDidLoad() 中:

self.MeatNameLabel.text = labelText