打破代码块中的保留环
诊断并修复传统应用中最常见的 ARC 内存泄漏：代码块捕获 self 导致的保留环，并学习使用弱引用和强引用。
打破代码块中的保留环 是 CoddyKit 上的免费 Objective-C iOS Development for Legacy & Enterprise Apps 课时。 这是第 4 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Objective-C iOS Development for Legacy & Enterprise Apps 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Objective-C iOS Development for Legacy & Enterprise Apps 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
What is a Retain Cycle?
A retain cycle happens when two objects strongly reference each other. Neither's count can reach zero, so neither is ever freed — a memory leak ARC cannot break for you.
Blocks Capture Strongly
An Objective-C block captures the variables it uses, including self — and it captures them strongly by default. This is the number one source of cycles.
A Cycle in Action
Here self owns the block (stored in a property), and the block strongly captures self. That mutual ownership leaks.
self.completion = ^{
[self refreshUI];
};The weak Qualifier
Break the cycle by capturing a weak reference to self. A weak reference does not increase the retain count.
__weak typeof(self) weakSelf = self;
self.completion = ^{
[weakSelf refreshUI];
};The weakSelf Pattern
The convention names the capture weakSelf using __weak typeof(self) so the type stays correct even if the class changes.
__weak typeof(self) weakSelf = self;weakSelf Can Become nil
A weak reference becomes nil the instant the object deallocates. If the block runs after that, messages to weakSelf are silently ignored — but partial access can be inconsistent.
The strongSelf Guard
Inside the block, promote weakSelf to a temporary strong reference so it cannot vanish mid-execution.
self.completion = ^{
__strong typeof(weakSelf) strongSelf = weakSelf;
if (strongSelf) {
[strongSelf refreshUI];
}
};When You Do NOT Need weakSelf
Not every block leaks. If self does not own the block — for example a one-shot block passed to a method and not stored — capturing self strongly is fine and even safer.
[UIView animateWithDuration:0.3 animations:^{
self.view.alpha = 0;
}];Delegate Cycles
The same rule applies to delegates: a delegate property should be weak so a view controller and its child do not retain each other.
@property (nonatomic, weak) id<MyDelegate> delegate;Finding Leaks
Tools to hunt cycles:
- Instruments > Leaks flags leaked allocations
- Memory Graph Debugger in Xcode visualizes retain cycles
- Log in
deallocto confirm objects are freed
Rule of Thumb
Ask: does self own this block, and does the block touch self? If both are yes, use weakSelf (plus a strongSelf guard for multi-step work).
Quick Check
Test your retain cycle knowledge.
Recap
You learned to break retain cycles:
- Blocks capture
selfstrongly by default - A cycle leaks when self owns a block that references self
- Use
__weak typeof(self) weakSelfto break it - Add a
strongSelfguard for multi-step work - Mark delegate properties
weak
Instruments and the Memory Graph confirm your fixes.
常见问题解答
「打破代码块中的保留环」课时是免费的吗？
是的 — 「打破代码块中的保留环」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Objective-C iOS Development for Legacy & Enterprise Apps 课程的其余内容，请升级到 CoddyKit PRO。 Objective-C iOS Development for Legacy & Enterprise Apps 课程共包含 4 节课。
「打破代码块中的保留环」这节课中我会学到什么？
诊断并修复传统应用中最常见的 ARC 内存泄漏：代码块捕获 self 导致的保留环，并学习使用弱引用和强引用。 你通过在浏览器中直接运行的动手代码来练习 Objective-C iOS Development for Legacy & Enterprise Apps，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Objective-C iOS Development for Legacy & Enterprise Apps 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Objective-C iOS Development for Legacy & Enterprise Apps 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 4 节课，共 4 节。
「打破代码块中的保留环」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Objective-C iOS Development for Legacy & Enterprise Apps 课中编写并运行代码吗？
能。每节 Objective-C iOS Development for Legacy & Enterprise Apps 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。
此课程中的所有课时
- 手动保留与释放（MRR）基础
- 自动引用计数（ARC）
- 弱引用与强引用
- 打破代码块中的保留环