objective-c 使用 alloc init 而不是 new
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Use of alloc init instead of new
提问by willc2
Learning Objective-C and reading sample code, I notice that objects are usually created using this method:
学习Objective-C并阅读示例代码，我注意到通常使用这种方法创建对象：
SomeObject *myObject = [[SomeObject alloc] init];
instead of:
代替：
SomeObject *myObject = [SomeObject new];
Is there a reason for this, as I have read that they are equivalent?
是否有原因，因为我已经读到它们是等效的？
采纳答案by Jeremy Stanley
There are a bunch of reasons here: http://macresearch.org/difference-between-alloc-init-and-new
这里有很多原因：http: //macresearch.org/difference-between-alloc-init-and-new
Some selected ones are:
一些选择的是：
newdoesn't support custom initializers (likeinitWithString)alloc-initis more explicit thannew
new不支持自定义初始值设定项（如initWithString）alloc-init比new
General opinion seems to be that you should use whatever you're comfortable with.
一般意见似乎是你应该使用任何你觉得舒服的东西。
回答by guitar_freak
Very old question, but I've written some example just for fun — maybe you'll find it useful ;)
很老的问题，但我写了一些例子只是为了好玩——也许你会发现它很有用；)
#import "InitAllocNewTest.h"
@implementation InitAllocNewTest
+(id)alloc{
NSLog(@"Allocating...");
return [super alloc];
}
-(id)init{
NSLog(@"Initializing...");
return [super init];
}
@end
In main function both statements:
在主函数中，两个语句：
[[InitAllocNewTest alloc] init];
and
和
[InitAllocNewTest new];
result in the same output:
导致相同的输出：
2013-03-06 16:45:44.125 XMLTest[18370:207] Allocating... 2013-03-06 16:45:44.128 XMLTest[18370:207] Initializing...
2013-03-06 16:45:44.125 XMLTest[18370:207] Allocating... 2013-03-06 16:45:44.128 XMLTest[18370:207] Initializing...
回答by Barry Wark
+newis equivalent to +alloc/-initin Apple's NSObjectimplementation. It is highly unlikely that this will ever change, but depending on your paranoia level, Apple's documentation for +newappears to allow for a change of implementation (and breaking the equivalency) in the future. For this reason, because "explicit is better than implicit" and for historical continuity, the Objective-C community generally avoids +new. You can, however, usually spot the recent Java comers to Objective-C by their dogged use of +new.
+new相当于+alloc/-init在苹果的NSObject实现中。这不太可能会改变，但根据您的偏执程度，Apple 的文档+new似乎允许将来更改实施（并打破等效性）。出于这个原因，因为“显式优于隐式”以及为了历史的连续性，Objective-C 社区通常避免+new. 但是，您通常可以通过他们顽固地使用+new.
回答by Brian Campbell
Frequently, you are going to need to pass arguments to initand so you will be using a different method, such as [[SomeObject alloc] initWithString: @"Foo"]. If you're used to writing this, you get in the habit of doing it this way and so [[SomeObject alloc] init]may come more naturally that [SomeObject new].
通常，您需要将参数传递给init，因此您将使用不同的方法，例如[[SomeObject alloc] initWithString: @"Foo"]. 如果你习惯写这个，你就会养成这样写的习惯，所以[[SomeObject alloc] init]可能会更自然地使用[SomeObject new].
回答by user739711
One Short Answere is:
一个简短的回答是：
- Both are same. But
- 'new' only works with the basic 'init' initializer, and will not work with other initializers (eg initWithString:).
- 两者都是一样的。但
- 'new' 仅适用于基本的 'init' 初始化程序，不能与其他初始化程序（例如 initWithString:）一起使用。
回答by MurderDev
I am very late to this but I want to mention that that new is actually unsafe in the Obj-C with Swift world. Swift will only create a default init method if you do not create any other initializer. Calling new on a swift class with a custom initializer will cause a crash. If you use alloc/init then the compiler will properly complain that init does not exist.
我对此很晚，但我想提一下，在 Swift 世界的 Obj-C 中，新的实际上是不安全的。如果您不创建任何其他初始化程序，Swift 只会创建一个默认的 init 方法。使用自定义初始值设定项在 swift 类上调用 new 将导致崩溃。如果您使用 alloc/init，那么编译器会正确地抱怨 init 不存在。
回答by evdude100
For a side note, I personally use [Foo new]if I want something in init to be done without using it's return value anywhere. If you do not use the return of [[Foo alloc] init]anywhere then you will get a warning. More or less, I use [Foo new]for eye candy.
附带说明一下，[Foo new]如果我希望在 init 中完成某些操作而不在任何地方使用它的返回值，我个人会使用它。如果您不使用[[Foo alloc] init]任何地方的返回，那么您将收到警告。或多或少，我[Foo new]用于眼睛糖果。
回答by Mike Crawford
If new does the job for you, then it will make your code modestly smaller as well. If you would otherwise call [[SomeClass alloc] init]in many different places in your code, you will create a Hot Spot in new's implementation - that is, in the objc runtime - that will reduce the number of your cache misses.
如果 new 为您完成了这项工作，那么它也会使您的代码小一些。如果您要[[SomeClass alloc] init]在代码中的许多不同位置调用，您将在 new 的实现中创建一个热点 - 即在 objc 运行时 - 这将减少缓存未命中的数量。
In my understanding, if you need to use a custom initializer use [[SomeClass alloc] initCustom].
据我了解，如果您需要使用自定义初始值设定项，请使用[[SomeClass alloc] initCustom].
If you don't, use [SomeClass new].
如果没有，请使用[SomeClass new].
