问题描述
今天我已经使用firstObject和objectAtIndex：0进行了测试。如果数组的大小为0，则使用前者不会导致崩溃，而后者会导致崩溃。所以我认为使用firstObject比使用objectAtIndex：0更好。但是在objectAtIndex上使用firstObject是否存在缺陷：0？
Today I have tested using firstObject and objectAtIndex:0. If the array has the size of 0, using the former does not cause a crash while the latter causes a crash. So I'm thinking that it's better to use firstObject than objectAtIndex:0. But are there pitfalls in using firstObject over objectAtIndex:0?
我也一直在阅读，我很惊讶并想知道为什么他们没有在文档中提到这个事实。
I have also been reading through the NSArray documentation and I am surprised and wondering why they did not mention this fact on the documentation.
推荐答案
有一个 键 的区别。如果没有，则使用 firstObject 返回 nil 。如果没有对象，使用 objectAtIndex：0 将使您的应用程序崩溃（抛出异常）。从用户体验的角度来看，崩溃是高度提倡的，所以它更安全使用 firstObject 。
There is one key difference. Using firstObject returns nil if there is none. Using objectAtIndex:0 will crash your app(throws an exception) if there is no object there.From a user experience perspective, crashing is highly advocated against, so it is safer to use firstObject.
但是 最大的陷阱： firstObject 自iOS 4开始提供，但在iOS 7之前是一个私有API。
BUT the biggest pitfall: firstObject has been available since iOS 4, but was a private API until iOS 7.
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