iOS “获取验证码”按钮的倒计时功能

Do it!

NS_ASSUME_NONNULL_BEGIN
@interface WLButtonCountdownManager : NSObject

/**
*  获取单例
*
*  @return 该类的唯一实例
*/
+ (instancetype)defaultManager;

/**
*  开始倒计时，如果倒计时管理器里具有相同的key，则直接开始回调。
*
*  @param aKey         任务key，用于标示唯一性
*  @param timeInterval 倒计时总时间，受操作系统后台时间限制，倒计时时间规定不得大于 120 秒.
*  @param countingDown 倒计时时，会多次回调，提供当前秒数
*  @param finished     倒计时结束时调用，提供当前秒数，值恒为 0
*/
- (void)scheduledCountDownWithKey:(NSString *)aKey
timeInterval:(NSTimeInterval)timeInterval
countingDown:(nullable void (^)(NSTimeInterval leftTimeInterval))countingDown
finished:(nullable void (^)(__unused NSTimeInterval finalTimeInterval))finished;

/**
*  查询倒计时任务是否存在
*
*  @param akey 任务key
*  @param task 任务
*  @return YES - 存在， NO - 不存在
*/
- (BOOL)coundownTaskExistWithKey:(NSString *)akey task:(NSOperation * _Nullable * _Nullable)task;

@end
NS_ASSUME_NONNULL_END

About timer

@interface WLCountdownTask : NSOperation
/**
*  计时中回调
*/
@property (copy, nonatomic) void (^countingDownBlcok)(NSTimeInterval timeInterval);
/**
*  计时结束后回调
*/
@property (copy, nonatomic) void (^finishedBlcok)(NSTimeInterval timeInterval);
/**
*  计时剩余时间
*/
@property (assign, nonatomic) NSTimeInterval leftTimeInterval;
/**
*  后台任务标识，确保程序进入后台依然能够计时
*/
@property (assign, nonatomic) UIBackgroundTaskIdentifier taskIdentifier;
@end

- (void)main {
self.taskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:nil];

while (--_leftTimeInterval > 0) {
dispatch_async(dispatch_get_main_queue(), ^{
if (_countingDownBlcok) _countingDownBlcok(_leftTimeInterval);
});

[NSThread sleepForTimeInterval:1];
}

dispatch_async(dispatch_get_main_queue(), ^{
if (_finishedBlcok) {
_finishedBlcok(0);
}
});

if (self.taskIdentifier != UIBackgroundTaskInvalid) {
[[UIApplication sharedApplication] endBackgroundTask:self.taskIdentifier];
self.taskIdentifier = UIBackgroundTaskInvalid;
}
}

@end

- (void)scheduledCountDownWithKey:(NSString *)aKey
timeInterval:(NSTimeInterval)timeInterval
countingDown:(void (^)(NSTimeInterval))countingDown
finished:(void (^)(NSTimeInterval))finished
{
if (timeInterval > 120) {
NSCAssert(NO, @"受操作系统后台时间限制，倒计时时间规定不得大于 120 秒.");
}

if (_pool.operations.count >= 20)  // 最多 20 个并发线程
return;

WLCountdownTask *task = nil;
if ([self coundownTaskExistWithKey:aKey task:&task]) {
task.countingDownBlcok = countingDown;
task.finishedBlcok     = finished;
if (countingDown) {
countingDown(task.leftTimeInterval);
}
} else {
task                   = [[WLCountdownTask alloc] init];
task.name              = aKey;
task.leftTimeInterval  = timeInterval;
task.countingDownBlcok = countingDown;
task.finishedBlcok     = finished;
[_pool addOperation:task];
}
}

- (BOOL)coundownTaskExistWithKey:(NSString *)akey
task:(NSOperation *__autoreleasing  _Nullable *)task
{
__block BOOL taskExist = NO;
[_pool.operations enumerateObjectsUsingBlock:^(__kindof NSOperation * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
if ([obj.name isEqualToString:akey]) {
if (task) *task = obj;
taskExist = YES;
*stop     = YES;
}
}];

return taskExist;
}

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