Question

这是我的代码（简化了一下）。我每秒都会触发一个NSTimer，它会从counter变量中减去一个。当应用程序进入后台时，我正在停止计数器并将计数器将达到零的时间保存到NSDefault值中。

然而，当从后台恢复应用程序时，当我从“零”时间减去当前时间时，我有时会得到太大的值。请帮我找一下这个bug？

- (void)prepareToEnterBackground {
    NSUserDefaults *defaults;
    defaults = [NSUserDefaults standardUserDefaults];

    [defaults setBool:[self timerIsRunning] forKey:@"timer_is_running"];
    [defaults setInteger:workPlayStatus forKey:@"work_play_status"];
    if ([self timerIsRunning]) {
        [defaults setFloat:([[NSDate date] timeIntervalSince1970] + (float) counter) forKey:@"timestamp_for_status_change"];
    } else {
        [defaults setFloat:0.0 forKey:@"timestamp_for_status_change"];
    }

    if (timer!=nil) {
        [timer invalidate];
        timer = nil;
    }
}

- (void)restoreFromBackground {
    NSUserDefaults *defaults;
    defaults = [NSUserDefaults standardUserDefaults];

    NSInteger remainingTimerSeconds;
    if ([defaults integerForKey:@"timer_is_running"]) {
        remainingTimerSeconds = (int) ([defaults floatForKey:@"timestamp_for_status_change"] - [[NSDate date] timeIntervalSince1970]);
        if (remainingTimerSeconds <= 0) {
            remainingTimerSeconds = 0;
        }
    } else {
        remainingTimerSeconds = 0;
    }

    if (remainingTimerSeconds > 0) {
        counter = remainingTimerSeconds;
        workPlayStatus = [defaults integerForKey:@"work_play_status"];
        timer = [NSTimer scheduledTimerWithTimeInterval:1 
            target:self
            selector:@selector(advanceTimer:)
            userInfo:nil
            repeats:YES];
    }
}

Answer 1

只是一个猜测 - NSTimeInterval类型被定义为double并且您在代码中使用浮点数，因此您可能会在某处溢出。尝试将float更改为double，这可能会有所帮助......

iOS背景中的倒计时问题

1 个答案: