iOS get the current date and day of the week, change the title of the navigation system back button

 // get the date

    NSArray * arrWeek=[ NSArray arrayWithObjects : @" Monday " , @" Tuesday " , @" Wednesday " , @" Thursday " , @" Friday " , @" Saturday " , @" Sunday " , nil ];

    NSDate *date = [NSDate date];

    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

    NSDateComponents *comps =[[NSDateComponentsalloc] init];

    NSInteger unitFlags = NSYearCalendarUnit |

    NSMonthCalendarUnit |

    NSDayCalendarUnit |

    NSWeekdayCalendarUnit |

    NSHourCalendarUnit |

    NSMinuteCalendarUnit |

    NSSecondCalendarUnit;

    comps = [calendar components:unitFlags fromDate:date];

    int week = [comps weekday];

    int year=[comps year];

    int month = [comps month];

    int day = [comps day];

    int hours=[comps hour];

    int minute=[comps minute];

    

    _dateLable.text=[NSString stringWithFormat:@"%d.%d.%d",year,month,day];

//    NSLog(@"_dateLable.text=%@",_dateLable.text);

    _weekLable.text=[NSString stringWithFormat:@"%@",[arrWeek objectAtIndex:week]];

    _timeLable.text=[NSString stringWithFormat:@"当前时间：%d:%d",hours,minute];

//    隐藏系统返回按钮的标签

      [[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(0, -60) forBarMetrics:UIBarMetricsDefault];