duration
Represents a positive or negative span of time.
构造函数
如果类型具有构造函数，可以像函数一样调用它来创建一个该类型的值。
Creates a new duration.
You can specify the duration using weeks, days, hours, minutes and seconds. You can also get a duration by subtracting two datetimes.
#duration(
days: 3,
hours: 12,
).hours()
seconds
The number of seconds.
默认：0
minutes
The number of minutes.
默认：0
hours
The number of hours.
默认：0
days
The number of days.
默认：0
weeks
The number of weeks.
默认：0
定义
函数和类型可以有与其关联的定义 (成员或方法)。可以使用 "." 操作符来访问调用它们。
seconds
The duration expressed in seconds.
This function returns the total duration represented in seconds as a floating-point number rather than the second component of the duration.
minutes
The duration expressed in minutes.
This function returns the total duration represented in minutes as a floating-point number rather than the second component of the duration.
hours
The duration expressed in hours.
This function returns the total duration represented in hours as a floating-point number rather than the second component of the duration.
days
The duration expressed in days.
This function returns the total duration represented in days as a floating-point number rather than the second component of the duration.
weeks
The duration expressed in weeks.
This function returns the total duration represented in weeks as a floating-point number rather than the second component of the duration.