我正在尝试创建一个日期选择器,并且需要在月份之间进行导航。
let current = NaiveDate::parse_from_str("2020-10-15", "%Y-%m-%d").unwrap();
我该如何生成日期 2020-11-15
?
我正在尝试创建一个日期选择器,并且需要在月份之间进行导航。
let current = NaiveDate::parse_from_str("2020-10-15", "%Y-%m-%d").unwrap();
我该如何生成日期 2020-11-15
?
这是我的解决方案:
use chrono::{ NaiveDate, Duration, Datelike};
fn get_days_from_month(year: i32, month: u32) -> u32 {
NaiveDate::from_ymd(
match month {
12 => year + 1,
_ => year,
},
match month {
12 => 1,
_ => month + 1,
},
1,
)
.signed_duration_since(NaiveDate::from_ymd(year, month, 1))
.num_days() as u32
}
fn add_months(date: NaiveDate, num_months: u32) -> NaiveDate {
let mut month = date.month() + num_months;
let year = date.year() + (month / 12) as i32;
month = month % 12;
let mut day = date.day();
let max_days = get_days_from_month(year, month);
day = if day > max_days { max_days } else { day };
NaiveDate::from_ymd(year, month, day)
}
fn main() {
let date = NaiveDate::parse_from_str("2020-10-31", "%Y-%m-%d").unwrap();
let new_date = add_months(date, 4);
println!("{:?}", new_date);
}
NaiveDate
现在有一个方法可以实现这个功能:checked_add_months
assert_eq!(
NaiveDate::from_ymd(2020, 10, 15).checked_add_months(chrono::Months::new(1)),
Some(NaiveDate::from_ymd(2020, 11, 15))
);
assert_eq!(
NaiveDate::from_ymd(2020, 10, 15).checked_add_months(chrono::Months::new(3)),
Some(NaiveDate::from_ymd(2021, 1, 15))
);
尝试使用 chronoutil crate。其中有 chronoutil::delta::shift_months 函数适用于任何 Datelike。
let current = NaiveDate::parse_from_str("2020-10-15", "%Y-%m-%d").unwrap();
let next = shift_months(current, 1);
assert_eq!(NaiveDate::parse_from_str("2020-11-15", "%Y-%m-%d").unwrap(), next);
注意:
如果月末日期存在歧义,则会向后移动。
所以对于2020-1-30,它会给出2020-2-29,而2021-1-30则变为2021-2-28。
let current = NaiveDate::parse_from_str("2021-1-30", "%Y-%m-%d").unwrap();
let next = shift_months(current, 1);
assert_eq!(NaiveDate::parse_from_str("2021-2-28", "%Y-%m-%d").unwrap(), next);
fn next_month(year: i32, month: u32) -> (i32, u32) {
assert!(month >= 1 && month <= 12);
if month == 12 {
(year + 1, 1)
} else {
(year, month + 1)
}
}
fn prev_month(year: i32, month: u32) -> (i32, u32) {
assert!(month >= 1 && month <= 12);
if month == 1 {
(year - 1, 12)
} else {
(year, month - 1)
}
}