iOS UITableView倒计时

背景：项目里需要实现每一行展示数据里面都有一个倒计时显示，倒计时结束，显示“已结束”
思路：
1、从服务器获取数据以后，启用定时器
2、定时器方法主要功能：
（1）更新数据源中的倒计时字段信息
（2）获取正在页面显示的cell，用来更新展示页面
界面展示：

UI.png

plist文件：

plist文件.png

代码如下：

#import "ViewController.h"
#import 

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UITableView *tableView;
@property (nonatomic, strong)NSMutableArray *dataArray;
@property (nonatomic, strong)NSTimer *timer;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    //从plist文件中加载数据源
    [self loadDataSource];
}
- (void)loadDataSource{
    NSString *dataPath = [[NSBundle mainBundle] pathForResource:@"dataList" ofType:@"plist"];
    self.dataArray = [[NSMutableArray alloc] initWithContentsOfFile:dataPath];
    if (self.dataArray) {
        [self startTimer];
    }
}
#pragma mark - 计时器
- (void)startTimer{
    if (self.timer == nil) {
        self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(refreshTime) userInfo:nil repeats:YES];
        //如果不添加这条语句，在UITableView拖动的时候，会阻塞定时器的调用
        [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:UITrackingRunLoopMode];
    }
}
- (void)endTimer{
    if(self.timer && self.timer.isValid){
        [self.timer invalidate];
        self.timer = nil;
    }
}
- (void)refreshTime{
    long long time;
    int unvaliableCount = 0;
    for (int i = 0; i < self.dataArray.count; i++) {
        NSMutableDictionary *dict = self.dataArray[i];
        time = [dict[@"leftDate"] longLongValue];
        if (time == 0) {
            ++unvaliableCount;
            continue;
        }
        time = time - 1000;
        dict[@"leftDate"] = [NSNumber numberWithLongLong:time];
    }
   NSMutableArray *visibleCell = [self.tableView valueForKey:@"_visibleCells"];
    for (UITableViewCell *cell in visibleCell) {
        NSMutableDictionary *dict = [self.dataArray objectAtIndex:cell.tag];
        long long cellTime = [dict[@"leftDate"] longLongValue];
        cell.detailTextLabel.text = [self getResuableTime:cellTime];
    }
//所有倒计时结束，计时器销毁    
if (unvaliableCount == self.dataArray.count) {
        [self endTimer];
    }
}
- (NSString *)getResuableTime:(long long)timeValue{
     if(timeValue <= 0){
        return @"已结束";
    }else{
        NSUInteger time = timeValue / 1000;
        NSUInteger hour = (NSUInteger)(time/3600);
        NSUInteger min  = (NSUInteger)(time%(3600))/60;
        NSUInteger second = (NSUInteger)(time%60);
        NSString *timeString = [NSString stringWithFormat:@"%02lu:%02lu:%02lu",(unsigned long)hour,(unsigned long)min,(unsigned long)second];
        return  timeString;
    }
}
#pragma mark - UITableView
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
    return self.dataArray.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
    static NSString *cellIdentifier = @"demoCell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:cellIdentifier];
    }
    cell.tag = indexPath.row;
    NSMutableDictionary *dict = [self.dataArray objectAtIndex:indexPath.row];
    cell.textLabel.text = dict[@"title"];
    long long cellTime = [dict[@"leftDate"] longLongValue];
    cell.detailTextLabel.text = [self getResuableTime:cellTime];
    return cell;
}
//查看UITableView属性
- (IBAction)printBtnAction:(UIButton *)sender {
    unsigned int count = 0;
    Ivar *members = class_copyIvarList([UITableView class], &count);
    for (int i = 0; i < count; i++) {
        Ivar var = members[i];
        const char *memberName = ivar_getName(var);
        const char *memberType = ivar_getTypeEncoding(var);
        NSLog(@"%s : %s",memberName,memberType);
    }
    NSLog(@"总数 %d",count);
}
@end