强/弱/保留/不安全_保留/分配 [英] strong / weak / retain / unsafe_unretained / assign

问题描述

合成属性的属性：
保留/分配

所有权属性：
IOS5 = strong / weak
IOS4 = retain / unsafe_unretained

• strong（iOS4 = retain） - 我的所有者，您不能dealloc这个
  之前目标精确= =



• （iOS4 = unsafe_unretained） - 与分配相同，不保留
  或发布

那么unsafe_unretained == assign？

  @property（nonatomic，assign）NSArray * tmp; 
  

等于？

  @property（nonatomic，unsafe_unretained）NSArray * tmp; 
  

反之亦然？

如果是这样，在iOS4中更喜欢哪一个，或者为什么还有（unsafe_unretained）如果与完全一样分配？

并且iOS4中的委托应该是unsafe_unretained或assign？

解决方案

更喜欢在iOS4中，或为什么有（unsafe_unretained）如果它完全一样分配？

你应该使用 unsafe_unretained 。你想显示你的代码的读者你实际想使用弱，但这是不可能的，因为weak是不可用的iOS版本你想部署。

有一天，您将放弃对iOS4的支持。然后你可以搜索 unsafe_unretained ，并用 weak 替换所有这些。这将比搜索 assign 更容易，并确定您是否实际上意味着分配或弱

使用 unsafe_unretained 创建更易读和可理解的代码，开发人员更容易看到。
基本上同样的原因，我们使用 YES 而不是 1 。

properties for synthesizing the property : retain / assign

• retain - it is retained, old value is released and it is assigned
• assign - it is only assigned

properties for ownership : IOS5 = strong / weak IOS4 = retain / unsafe_unretained

• strong (iOS4 = retain) - i'am the owner, you cannot dealloc this before aim fine with that = retain

• weak (iOS4 = unsafe_unretained) - the same thing as assign, no retain or release

so unsafe_unretained == assign?

@property (nonatomic, assign) NSArray * tmp;

is equal to ?

@property (nonatomic, unsafe_unretained) NSArray * tmp;

and vice versa ?

if so, which one to prefer when in iOS4, or why there is (unsafe_unretained) if its exactly same as assign?

and a delegate in iOS4 should be unsafe_unretained or assign?

解决方案

if so, which one to prefer when in iOS4, or why there is (unsafe_unretained) if its exactly same as assign?

you should use unsafe_unretained. You want to show the reader of your code that you actually wanted to use weak but that this was not possible because weak is not available on the iOS version you want to deploy.

One day you will drop the support for iOS4. And then you could just search for unsafe_unretained and replace all of them with weak. This will be much easier than searching for assign and figuring out if you actually meant assign or weak

The use of unsafe_unretained creates more readable and understandable code where the intentions of the developer are easier to see. Basically the same reason we use YES instead of 1.

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