NSCalendar dateFromComponents: vs NSDateComponents 日期 [英] NSCalendar dateFromComponents: vs NSDateComponents date

问题描述

假设我有以下初始化 NSDateComponents 的代码:

Say I have the following code which initializes an NSDateComponents:

NSCalendar *calendar = [NSCalendar currentCalendar];

NSDateComponents *components = [[NSDateComponents alloc] init];
[components setYear:1987];
[components setMonth:3];
[components setDay:17];
[components setHour:14];
[components setMinute:20];
[components setSecond:0];

现在我想将组件转换为 NSDate.好像有两种方法:

And now I want to convert the components to an NSDate. It seems like there are two ways:

方法一:

NSDate *date = [calendar dateFromComponents:components];

方法二:

NSDate *date = [components date];

这两种方法有区别吗?如果是，应该使用哪一个?为什么?

Is there a difference between these two methods? If so, which one should be used and why?

推荐答案

NSDate *date = [components date];

与

NSDate *date = [[components calendar] dateFromComponents:comps];

如果您没有为日期组件分配日历，它会返回 nil.您可以通过设置环境变量 NSObjCMessageLoggingEnabled=YES 来验证在项目方案中，并在生成的消息跟踪 (/tmp/msgSends-NNNN) 中观察到调用的方法完全相同.

and it returns nil if you don't have assigned a calendar to the date components. You can verify that by setting the environment variable NSObjCMessageLoggingEnabled=YES in the projects scheme, and observe in the generated message trace (/tmp/msgSends-NNNN) that exactly the same methods are called.

这意味着你可以调用

NSDate *date = [calendar dateFromComponents:components];

或

[components setCalendar:calendar];
NSDate *date = [components date];

并且这两种方法没有区别.

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