Question

我感到困惑的是,在目标C中分配记忆的适当手段是,我有一位有叙文的人。我可以采取两种方法:

   NSMutableDictionary *alpha = [[NSMutableDictionary alloc] init];

或

   NSMutableDictionary *alpha = [NSMutableDictionary dictionary];

What is the difference between them? I know the first allocates mem或y f或 alpha, but what about the second?

Which of these is recommended as the best practice f或 allocating mem或y?

Answer 1

[NSMutableDictionary dictionary];

确实与以下方面相同:

[[[NSMutableDictionary alloc] init] autorelease];

这只是拯救了你们一些打字。只要你知道保留物体与自动释放物体之间的区别,你就会使用。如果你重新使用非洲排雷中心,那么你甚至不需要知道这一点。

The convention is:

If you see init, new or copy: it s a retained object.
If the method name starts with the class name (sans the framework prefix), it s an autoreleased object.

Answer 2

<代码>[NSMutableDictionary dictionary]是NSMutableDictionary<>_code>的类别方法。该表载有对<代码>alloc和init的电话,就像你手工操作一样。由于这是一个非常常用的类别,作者包括这一所谓的“要素方法”,以使他/她的阶层的使用者的生活更加容易。

见。关于这一模式的更多细节。

As for which is good practice, IMHO you should use the factory method. It makes your own code more readable and saves you typing. Moreover - although I am not sure if this is the case with NSMutableDictionary - using the factory method makes maintenance easier for both its developers and yourself, because they are e. g. free to change the concrete subclass implementation you will receive from the factory, without having you change your application code.

As correctly pointed out it the comments, factory methods like this return autoreleased instances of objects, so if you only use them locally in a method, there is no need to worry about them from a memory management point of view. For more details on memory management, autorelease and the new ARC runtime with automatic reference counting, you should deep dive into Apple s documentation on the topic, if you haven t already.

Answer 3

这两行都将为甲型六氯环己烷分配记忆,差异是甲型六氯环己烷是自动释放物体。

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