NSTimer iPhone从当前时间恢复

Question

这是我的iPhone秒表应用程序的代码，当你点击开始按钮时，它将以正确的格式计数，所有工作正常，以及停止按钮和重置。问题是每次我点击停止，然后再次开始它创建一个新的计时器，不继续从最后一个。我如何创建暂停并能够从当前时间继续?

感谢

NSDate *startDate;
NSTimer *stopWatchTimer;

-(void)showActivity {
    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:startDate];
    NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"mm:ss.SS"];
    [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
    NSString *timeString=[dateFormatter stringFromDate:timerDate];
    stopWatchLabel.text = timeString;
    [dateFormatter release];
}
- (IBAction)onStartPressed:(id)sender {
    startDate = [[NSDate date]retain];
    stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1/10 target:self selector:@selector(showActivity) userInfo:nil repeats:YES];
}
- (IBAction)onStopPressed:(id)sender {
    [stopWatchTimer invalidate];
    stopWatchTimer = nil;
    [self showActivity];
}
- (IBAction)reset:(id)sender; {
    stopWatchLabel.text = @"00:00.00";
}

Answer 1

在Pause期间，您可能希望将timeInterval保留为iVar

accumulatedInterval = [currentDate timeIntervalSinceDate:startDate];

Answer 2

不要在每次开始时都设置startDate。只在第一次重置之后。