1 #import <UIKit/UIKit.h>2 3 @interface ViewController : UIViewController4 @PRoperty (assign, nonatomic) NSInteger surplusSecond;5 6 @property (strong, nonatomic) IBOutlet UILabel *lblMessage;7 @property (strong, nonatomic) IBOutlet UIButton *btnSendCAPTCHA;8 9 @end

 1 #import "ViewController.h" 2  3 @interface ViewController () 4 - (void)layoutUI; 5 - (void)countDown; 6 @end 7  8 @implementation ViewController 9 #define kSurplusSecond 510 11 - (void)viewDidLoad {12     [super viewDidLoad];13     14     [self layoutUI];15 }16 17 - (void)didReceiveMemoryWarning {18     [super didReceiveMemoryWarning];19     // Dispose of any resources that can be recreated.20 }21 22 - (void)layoutUI {23     _surplusSecond = kSurplusSecond; //剩余秒數；這里指驗證碼發送完，間隔多少秒才能再次點擊「驗證」按鈕進行發送驗證碼24     25     _btnSendCAPTCHA.tintColor = [UIColor darkGrayColor];26     _btnSendCAPTCHA.layer.masksToBounds = YES;27     _btnSendCAPTCHA.layer.cornerRadius = 10.0;28     _btnSendCAPTCHA.layer.borderColor = [UIColor grayColor].CGColor;29     _btnSendCAPTCHA.layer.borderWidth = 1.0;30 }31 32 /**33  *  倒計時34  */35 - (void)countDown {36     //全局并發隊列37     dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);38     //主隊列；屬于串行隊列39     dispatch_queue_t mainQueue = dispatch_get_main_queue();40     41     //定時循環執行事件42     //dispatch_source_set_timer 方法值得一提的是最后一個參數（leeway），他告訴系統我們需要計時器觸發的精準程度。所有的計時器都不會保證100%精準，這個參數用來告訴系統你希望系統保證精準的努力程度。如果你希望一個計時器每5秒觸發一次，并且越準越好，那么你傳遞0為參數。另外，如果是一個周期性任務，比如檢查email，那么你會希望每10分鐘檢查一次，但是不用那么精準。所以你可以傳入60，告訴系統60秒的誤差是可接受的。他的意義在于降低資源消耗。43     dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, globalQueue);44     dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC, 0.0 * NSEC_PER_SEC);45     dispatch_source_set_event_handler(timer, ^{ //計時器事件處理器46         NSLog(@"Event Handler");47         if (_surplusSecond <= 0) {48             dispatch_source_cancel(timer); //取消定時循環計時器；使得句柄被調用，即事件被執行49             dispatch_async(mainQueue, ^{50                 _btnSendCAPTCHA.enabled = YES;51                 [_btnSendCAPTCHA setTitle:@"驗證" forState:UIControlStateNormal];52                 53                 _lblMessage.text = @"使用 GCD 實現倒計時效果";54                 _surplusSecond = kSurplusSecond;55             });56         } else {57             _surplusSecond--;58             dispatch_async(mainQueue, ^{59                 NSString *btnInfo = [NSString stringWithFormat:@"%ld秒", (long)(_surplusSecond + 1)];60                 _btnSendCAPTCHA.enabled = NO;61                 [_btnSendCAPTCHA setTitle:btnInfo forState:UIControlStateDisabled];62             });63         }64     });65     dispatch_source_set_cancel_handler(timer, ^{ //計時器取消處理器；調用 dispatch_source_cancel 時執行66         NSLog(@"Cancel Handler");67     });68     dispatch_resume(timer);  //恢復定時循環計時器；Dispatch Source 創建完后默認狀態是掛起的，需要主動恢復，否則事件不會被傳遞，也不會被執行69 }70 71 - (IBAction)sendCAPTCHA:(id)sender {72     _lblMessage.text = [NSString stringWithFormat:@"驗證碼發送成功，%d秒后可重新發送", kSurplusSecond];73     74     [self countDown];75 }76 77 @end

 1 <?xml version="1.0" encoding="UTF-8" standalone="no"?> 2 <document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="7706" systemVersion="14E46" targetRuntime="iOS.CocoaTouch" propertyaccessControl="none" useAutolayout="YES" useTraitCollections="YES" initialViewController="vXZ-lx-hvc"> 3     <dependencies> 4         <deployment identifier="iOS"/> 5         <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="7703"/> 6     </dependencies> 7     <scenes> 8         <!--View Controller--> 9         <scene sceneID="ufC-wZ-h7g">10             <objects>11                 <viewController id="vXZ-lx-hvc" customClass="ViewController" sceneMemberID="viewController">12                     <layoutGuides>13                         <viewControllerLayoutGuide type="top" id="jyV-Pf-zRb"/>14                         <viewControllerLayoutGuide type="bottom" id="2fi-mo-0CV"/>15                     </layoutGuides>16                     <view key="view" contentMode="scaleToFill" id="kh9-bI-dsS">17                         <rect key="frame" x="0.0" y="0.0" width="600" height="600"/>18                         <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMaxY="YES"/>19                         <subviews>20                             <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="使用 GCD 實現倒計時效果" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="1Kh-pV-cfz">21                                 <rect key="frame" x="200" y="289.5" width="200" height="20.5"/>22                                 <fontDescription key="fontDescription" type="system" pointSize="17"/>23                                 <color key="textColor" cocoaTouchSystemColor="darkTextColor"/>24                                 <nil key="highlightedColor"/>25                             </label>26                             <button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="rFe-Xb-ZSc">27                                 <rect key="frame" x="240" y="510" width="120" height="50"/>28                                 <constraints>29                                     <constraint firstAttribute="width" constant="120" id="gVH-aT-gen"/>30                                     <constraint firstAttribute="height" constant="50" id="jJP-Vc-fpy"/>31                                 </constraints>32                                 <state key="normal" title="驗證">33                                     <color key="titleShadowColor" white="0.5" alpha="1" colorSpace="calibratedWhite"/>34                                 </state>35                                 <connections>36                                     <action selector="sendCAPTCHA:" destination="vXZ-lx-hvc" eventType="touchUpInside" id="I6T-s9-9H6"/>37                                 </connections>38                             </button>39                         </subviews>40                         <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="calibratedWhite"/>41                         <constraints>42                             <constraint firstAttribute="centerX" secondItem="rFe-Xb-ZSc" secondAttribute="centerX" id="CoE-CP-eDN"/>43                             <constraint firstAttribute="centerY" secondItem="1Kh-pV-cfz" secondAttribute="centerY" id="bX4-jS-0xm"/>44                             <constraint firstAttribute="centerX" secondItem="1Kh-pV-cfz" secondAttribute="centerX" id="mKH-Zw-Utb"/>45                             <constraint firstItem="2fi-mo-0CV" firstAttribute="top" secondItem="rFe-Xb-ZSc" secondAttribute="bottom" constant="40" id="y3Q-IA-qIO"/>46                         </constraints>47                     </view>48                     <connections>49                         <outlet property="btnSendCAPTCHA" destination="rFe-Xb-ZSc" id="UFG-TS-ImX"/>50                         <outlet property="lblMessage" destination="1Kh-pV-cfz" id="gzx-3T-euc"/>51                     </connections>52                 </viewController>53                 <placeholder placeholderIdentifier="IBFirstResponder" id="x5A-6p-PRh" sceneMemberID="firstResponder"/>54             </objects>55         </scene>56     </scenes>57 </document>

1 2015-08-31 14:40:02.083 KMCountDown[5102:103949] Event Handler2 2015-08-31 14:40:03.087 KMCountDown[5102:103949] Event Handler3 2015-08-31 14:40:04.084 KMCountDown[5102:103949] Event Handler4 2015-08-31 14:40:05.086 KMCountDown[5102:103971] Event Handler5 2015-08-31 14:40:06.085 KMCountDown[5102:103949] Event Handler6 2015-08-31 14:40:07.085 KMCountDown[5102:103949] Event Handler7 2015-08-31 14:40:07.085 KMCountDown[5102:103949] Cancel Handler