解决iOS程序UI主线程和定时器相互阻塞的问题

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此文是接上文http://www.cnblogs.com/zzltjnh/archive/2013/05/15/3080058.html问题解决之后遇到的一个新问题，我的页面上有一个UIScrollView和一个定时器用来记录当前考试模式下的剩余时间，问题出现了：当我滑动滚动试图时，定时器的方法便不在运行（即被UI主线程阻塞）。google一下找到了解决办法：将定时器放在非主线程中执行将更新UI的操作放到主线程，这样UI主线程和定时器就能互不干扰的相互工作了，以下是主要代码：

#import "CountdownTool.h"@interface CountdownTool(){    UILabel *_lblShow;    NSTimer *_timer;}@property (nonatomic, assign) NSInteger hour;@property (nonatomic, assign) NSInteger minute;@property (nonatomic, assign) NSInteger second;@property (nonatomic, copy) NSString  *strHour;@property (nonatomic, copy) NSString  *strMinute;@property (nonatomic, copy) NSString  *strSecond;@property (nonatomic, assign) NSInteger totalSeconds;@end@implementation CountdownTool@synthesize hour = _hour;@synthesize minute = _minute;@synthesize second = _second;@synthesize totalSeconds = _totalSeconds;- (void)dealloc{    [_lblShow release];    [_strHour release];    [_strMinute release];    [_strSecond release];    [super dealloc];}- (id)initWithFrame:(CGRect)frame{    self = [super initWithFrame:frame];    if (self) {        _lblShow = [[UILabel alloc] initWithFrame:self.bounds];        _lblShow.backgroundColor = [UIColor clearColor];        _lblShow.font = [UIFont systemFontOfSize:15];        _lblShow.textColor = [UIColor yellowColor];        _lblShow.textAlignment = NSTextAlignmentCenter;        _lblShow.numberOfLines = 1;        [self addSubview:_lblShow];    }    return self;}- (id)initWithFrame:(CGRect)frame andMinutesNum:(NSInteger)minute{    if (self = [self initWithFrame:frame]) {        self.totalSeconds = minute * 60;        //多线程启动定时器       [NSThread detachNewThreadSelector:@selector(startTimer) toTarget:self withObject:nil];    }    return self;}- (void)startTimer{    _timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(timerFire) userInfo:nil repeats:YES];    [[NSRunLoop currentRunLoop] run];}- (void)handleWithTotalSeconds{    self.hour = _totalSeconds/3600;    self.minute = _totalSeconds%3600/60;    self.second = _totalSeconds%3600%60;    if (_hour <= 0) {        _lblShow.text = [NSString stringWithFormat:@"%@:%@",_strMinute,_strSecond];    }else{        _lblShow.text = [NSString stringWithFormat:@"%@:%@:%@",_strHour,_strMinute,_strSecond];    }}- (void)setHour:(NSInteger)hour{    _hour = hour;    if (_hour < 10) {        self.strHour = [NSString stringWithFormat:@"0%d",_hour];    }else{        self.strHour = [NSString stringWithFormat:@"%d",_hour];    }}- (void)setMinute:(NSInteger)minute{    _minute = minute;    if (_minute < 10) {        self.strMinute = [NSString stringWithFormat:@"0%d",_minute];    }else{        self.strMinute = [NSString stringWithFormat:@"%d",_minute];    }}- (void)setSecond:(NSInteger)second{    _second = second;    if (_second < 10) {        self.strSecond = [NSString stringWithFormat:@"0%d",_second];    }else{        self.strSecond = [NSString stringWithFormat:@"%d",_second];    }}- (void)setTotalSeconds:(NSInteger)totalSeconds{    _totalSeconds = totalSeconds;    [self performSelectorOnMainThread:@selector(handleWithTotalSeconds) withObject:nil waitUntilDone:YES];}- (void)timerFire{    if (_totalSeconds == 0) {        [_timer invalidate];        return;    }    self.totalSeconds -= 1;}@end

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