一、Runloop

無輸入的sources 或 timers事件源，那么runloop會立即退出。

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一、PerformSelector延遲事件

perform(<#T##aSelector: Selector##Selector#>, with: <#T##Any?#>, afterDelay: <#T##TimeInterval#>)
作用向當(dāng)前Runloop添加一個(gè)timer事件源

1.1、在子線程執(zhí)行未開啟runloop

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesBegan(touches, with: event)
        print("touchesBegan1")
        DispatchQueue.global().asyncAfter(deadline: .now() + 3) { [self] in
            print("touchesBegan2")
            self.perform(#selector(onPerformAction), with: nil, afterDelay: 1)
            print("touchesBegan3")
        }
        print("touchesBegan4")
    }
    
    @objc func onPerformAction() {
        print("onPerformAction:\(Thread.current)");
    }

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1.2、在子線程執(zhí)行開啟runloop 結(jié)果: 執(zhí)行onPerformAction成功

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesBegan(touches, with: event)
        print("touchesBegan1")
        DispatchQueue.global().asyncAfter(deadline: .now() + 3) { [self] in
            print("touchesBegan2")
            // 下面這行代碼等于向當(dāng)前runloop添加timer事件源
            self.perform(#selector(onPerformAction), with: nil, afterDelay: 1)
           // 開啟runloop時(shí)，已經(jīng)有timer事件源，所以runloop不會因?yàn)闊o任何事件源而退出
            RunLoop.current.run()
            print("touchesBegan3")
        }
        print("touchesBegan4")
    }

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1.3、在子線程執(zhí)行開啟runloop 結(jié)果：執(zhí)行onPerformAction失敗

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
       super.touchesBegan(touches, with: event)
       print("touchesBegan1")
       DispatchQueue.global().asyncAfter(deadline: .now() + 3) { [self] in
           print("touchesBegan2")
           RunLoop.current.run()
           self.perform(#selector(onPerformAction), with: nil, afterDelay: 1)
           print("touchesBegan3")
       }
       print("touchesBegan4")
   }

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1.4、取消PerformSelector延遲事件

@objc func onCancelPerformAction() {
        /** 1.單獨(dú)取消perform的執(zhí)行事件*/
        NSObject.cancelPreviousPerformRequests(withTarget: self, selector: #selector(onPerformAction), object: nil)
        /** 2.取消perform的所有執(zhí)行事件*/
        NSObject.cancelPreviousPerformRequests(withTarget: self)
    }