NSArray：lastObject是否返回一个自动释放的对象？ [英] Does NSArray:lastObject return an autoreleased object?

问题描述

我正在一个iPhone项目，我想从一个NSMutableArray检索一个对象，从数组中删除对象，然后使用它。代码看起来像这样：

I'm working on an iPhone project where I would like to retrieve an object from an NSMutableArray, remove the object from the array and then use it later. The code looks something like this:

NSMutableArray * array;
// fill the array
NSObject * obj = [array lastObject];
[array removeLastObject];
// do something with obj (in the same function)

在被访问的对象上有一个retain。这是安全吗？我想假设这只会工作，如果lastObject自动释放对象，这是一个我不能弄清楚如果它。

array is the only entity with a retain on the object that is being accessed. Is this safe to do? I would assume that this would only work if lastObject autoreleased the object which is something that I can't figure out if it does.

推荐答案

为什么不调用

[array removeLastObject]

在函数的结尾？这是少一个释放/保留。

at the end of your function? That's one fewer release/retain. It might make your code more readable/less cluttered.

对于记录， Apple文档：

与NSArray类似，
NSMutableArray的实例对它们的内容保持强的
引用。如果你
不使用垃圾收集，当
你添加一个对象到数组，
对象接收一个保留消息。当
从一个可变的
数组中删除一个对象时，它接收一个释放消息。
如果没有进一步引用
对象，这意味着对象
被释放。如果你的程序保持
对这样的对象的引用，
引用将变得无效，除非
在从数组中删除之前发送对象一个保留消息
。
例如，如果anObject在从
数组中删除之前不保留
，则下面的第三个语句可能会导致运行时错误：

Like NSArray, instances of NSMutableArray maintain strong references to their contents. If you do not use garbage collection, when you add an object to an array, the object receives a retain message. When an object is removed from a mutable array, it receives a release message. If there are no further references to the object, this means that the object is deallocated. If your program keeps a reference to such an object, the reference will become invalid unless you send the object a retain message before it’s removed from the array. For example, if anObject is not retained before it is removed from the array, the third statement below could result in a runtime error:

id anObject = [[anArray objectAtIndex:0] retain]; 
[anArray removeObjectAtIndex:0]; 
[anObject someMessage];

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