快速计时器目标以防止保留周期

Question

在iOS 10之前，直接使用Timer会产生Retain Cycle，所以我使用Runtime来构建代码，但是代码在构建时崩溃了。不知道空指针是从哪里产生的。

var time: Timer?
var target: NSObject?


target = NSObject()
let selector = #selector(timePrint)
if let method = class_getMethodImplementation(self.classForCoder, selector) {
     let IMP = method_getImplementation(method)
     let encodeing = method_getTypeEncoding(method)
     class_addMethod(target?.classForCoder, selector, IMP, encodeing)
     time = Timer.scheduledTimer(timeInterval: 2, target: target!, selector: selector, userInfo: nil, repeats: true)
}

Answer 1

因为我想兼容iOS 10之前的老版本，所以只能这样。目前已知的方法如下：

• 模拟系统的关闭

extension Timer {
    class func rp_scheduledTimer(timeInterval ti: TimeInterval, repeats yesOrNo: Bool, closure: @escaping (Timer) -> Void) -> Timer {
        return self.scheduledTimer(timeInterval: ti, target: self, selector: #selector(RP_TimerHandle(timer:)), userInfo: closure, repeats: yesOrNo)
}
    
    @objc class func RP_TimerHandle(timer: Timer) {
        var handleClosure = { }
        handleClosure = timer.userInfo as! () -> ()
        handleClosure()
    }
}

if #available(iOS 10.0, *) {
      time = Timer.scheduledTimer(withTimeInterval: 2, repeats: true, block: { [weak self] (timer) in
            // do something
      })
} else {
      time = Timer.rp_scheduledTimer(timeInterval: 2, repeats: true, closure: { [weak self] (timer) in
            // do something
      })
}

• DispatchSource 替换 Timer

var source: DispatchSourceTimer?

if #available(iOS 10.0, *) {

} else {

   source = DispatchSource.makeTimerSource(flags: [], queue: .global())
   source.schedule(deadline: .now(), repeating: 2)
   source.setEventHandler {
       // do something...
   }
   source.resume()
}

• NSProxy