iOS 时间戳转换及两个时间差

   //时间戳
    NSString *beginTimestamp = @"1489586485";
    NSString *endTimestamp = @"1489811147";
    
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"yyyy-MM-dd-HH:MM:ss"];
    
    NSDate *date = [NSDate dateWithTimeIntervalSince1970:[beginTimestamp doubleValue]];
    NSString *dateString = [formatter stringFromDate:date];
    NSLog(@"开始时间: %@", dateString);
    
    NSDate *date2 = [NSDate dateWithTimeIntervalSince1970:[endTimestamp doubleValue]];
    NSString *dateString2 = [formatter stringFromDate:date2];
    NSLog(@"结束时间: %@", dateString2);
    
    NSTimeInterval seconds = [date2 timeIntervalSinceDate:date];
    NSLog(@"两个时间相隔：%f", seconds);