释放后将对象设置为 nil -- TT_RELEASE_SAFELY

发布于 2024-11-06 06:37:12 字数 487 浏览 0 评论 0原文

我已经开始学习 Three20，我有一个关于 TT_RELEASE_SAFELY 的简单问题到目前为止，我喜欢这样编写代码：

UILabel *lab = [[UILabel alloc] initWithFrame:rect];
[self.view addSubview:lab];
[lab release];

这里我认为主池负责释放lab的内存。

现在我发现 TT_RELEASE_SAFELY 的定义如下：

#define TT_RELEASE_SAFELY(__POINTER) { [__POINTER release]; __POINTER = nil; }

如您所见，释放后，它将对象设置为 nil。

我想知道这两种方式的区别以及哪种方式更好。

谢谢。

原文

I have started to study Three20 and I have a simple question about TT_RELEASE_SAFELY
Up till now I like to write code in this way:

UILabel *lab = [[UILabel alloc] initWithFrame:rect];
[self.view addSubview:lab];
[lab release];

Here I think the main pool is responsible to free the memory of lab.

Now I have found TT_RELEASE_SAFELY which is defined like so:

#define TT_RELEASE_SAFELY(__POINTER) { [__POINTER release]; __POINTER = nil; }

As you can see, after release, it sets the object to nil.

I'd like to know the difference between the two ways and which way is better.

Thanks.

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陌伤ぢ 2024-11-13 06:37:12

向 nil 发送消息在 Objective-C 中是有效的。向已释放的对象发送消息则不然。

向已释放的对象发送消息：

id obj = [[MyClass alloc] init];
[obj release];
[obj doSomething]; // Crash!

向 nil 发送消息：

id obj = [[MyClass alloc] init];
[obj release], obj = nil;
[obj doSomething]; // Valid

在对象被释放后将 nil 分配给变量是有争议的，因为它会阻止您意识到出现问题。 Sedate Alien 的示例：

[controlCenter dealloc];
...
float timeLeft = [controlCenter timeToWaitBeforeBombDetonation];

由于 controlCenter 已被释放，此代码将崩溃。因此，该缺陷将被及早发现并修复。

[controlCenter dealloc], controlCenter = nil;
...
float timeLeft = [controlCenter timeToWaitBeforeBombDetonation];

此代码将向 timeLeft 分配 0.0，即使 controlCenter 为零，这似乎也是有效的等待时间。

对上述内容持保留态度，因为如果您正在编写 Objective-C 应用程序，您可能更关心通过避免崩溃来让用户满意，而不是破坏城市。如果后者是一个问题，您可能应该使用类型安全的语言，例如 Ada。

Sending a message to nil is valid in Objective-C. Sending a message to a deallocated object is not.

Sending a message to a deallocated object:

id obj = [[MyClass alloc] init];
[obj release];
[obj doSomething]; // Crash!

Sending a message to nil:

id obj = [[MyClass alloc] init];
[obj release], obj = nil;
[obj doSomething]; // Valid

Assigning nil to a variable after an object has been deallocated is controversial because it can prevent you from realizing that something is wrong. Sedate Alien's example:

[controlCenter dealloc];
...
float timeLeft = [controlCenter timeToWaitBeforeBombDetonation];

This code will crash since controlCenter has been deallocated. As a result this defect will be detected and fixed early.

[controlCenter dealloc], controlCenter = nil;
...
float timeLeft = [controlCenter timeToWaitBeforeBombDetonation];

This code will assign 0.0 to timeLeft which appears to be a valid wait time even though controlCenter is nil.

Take the above with a grain of salt, since if you are writing an Objective-C app, you are probably more concerned with keeping your users happy by avoiding crashes than destroying cities. If the latter is a concern, you should probably be using a type-safe language like Ada.

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