Swift 4 计时器因 NSException 而崩溃

Question

我一直在寻找一种在 Swift 4 中使用计时器的方法并查看了 this文章。我在 xcode 中测试我的代码，当计时器第一次计时(在本例中为 10 秒后)时，应用程序崩溃并且我收到错误，尽管构建成功。

2017-11-20 19:54:42.781502-0700 Rock Prodigy[3022:554505] -[_SwiftValue   tick]: unrecognized selector sent to instance 0x608000051520
2017-11-20 19:54:42.791278-0700 Rock Prodigy[3022:554505] ***  Terminating app due to uncaught exception 'NSInvalidArgumentException',   reason: '-[_SwiftValue tick]: unrecognized selector sent to instance  0x608000051520'
*** First throw call stack:
(
0   CoreFoundation                      0x000000010360d1ab __exceptionPreprocess + 171
1   libobjc.A.dylib                     0x0000000102ca2f41 objc_exception_throw + 48
2   CoreFoundation                      0x000000010368da34 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
3   CoreFoundation                      0x00000001035900a8 ___forwarding___ + 1432
4   CoreFoundation                      0x000000010358fa88 _CF_forwarding_prep_0 + 120
5   Foundation                          0x000000010270e1ee __NSFireTimer + 83
6   CoreFoundation                      0x000000010359d2a4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20
7   CoreFoundation                      0x000000010359cf62 __CFRunLoopDoTimer + 1026
8   CoreFoundation                      0x000000010359cb1a __CFRunLoopDoTimers + 266
9   CoreFoundation                      0x0000000103594534 __CFRunLoopRun + 2308
10  CoreFoundation                      0x00000001035939b9 CFRunLoopRunSpecific + 409
11  GraphicsServices                    0x00000001090e29c6 GSEventRunModal + 62
12  UIKit                               0x0000000103a885e8 UIApplicationMain + 159
13  Rock Prodigy                        0x000000010238b637 main + 55
14  libdyld.dylib                       0x0000000107aa1d81 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

这是我的 swift 4 代码

import UIKit

class GeneralFitness: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    var timer: Timer! = Timer.scheduledTimer(timeInterval: 10, target: self, selector: #selector(tick), userInfo: nil, repeats: true)

    @objc func tick() {
        print("tick")
    }


}

如果您有任何问题，请告诉我。

Answer 1

作为Andrea said ，您应该在 viewDidLoad 中实例化计时器。还有 the documentation says :

The selector should have the following signature: timerFireMethod: (including a colon to indicate that the method takes an argument).

并且不要忘记在例如 viewDidDisappear 中禁用此计时器。您不能在 deinit 中invalidate 它，因为重复计时器保持对其目标的强引用，并且您的 deinit 不会被调用因为计时器正在运行。如果您在 viewDidDisappear 中删除它，您可能需要在 viewDidAppear 中创建计时器。

因此，结果如下:

class ViewController: UIViewController {

    weak var timer: Timer?

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        timer = Timer.scheduledTimer(timeInterval: 10, target: self, selector: #selector(tick(_:)), userInfo: nil, repeats: true)
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)

        timer?.invalidate()
    }

    @objc func tick(_ timer: Timer) {
        print("tick")
    }

}

或者您可以使用基于 block 的再现，使用 [weak self] 模式，计时器不会保持对 View Controller 的强引用，在这种情况下您可以 使用 deinit:

class ViewController: UIViewController {

    var timer: Timer?

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        timer = Timer.scheduledTimer(withTimeInterval: 10, repeats: true) { [weak self] timer in  // the `[weak self] reference is only needed if you reference `self` in the closure
            print("tick")
        }
    }

    deinit {
        timer?.invalidate()
    }

}