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Interface and API

15. Use Prefix Names to Avoid Namespace Clashes​

为类名添加前缀，与你的公司或应用名相关。

16: Have a Designated Initializer​

提供一个 designated initializer，其它的初始化方法均应调用此方法。

17: Implement the description Method​

This compact description can be used by forming a dictionary within your own description method and returning a string containing this dictionary’s description method.

- (NSString *)description {
    return [NSString stringWithFormat:@"<%@: %p, %@>",
            [self class],
            self,
            @{@"title":_title,
              @"latitude":@(_latitude),
              @"longitude":@(_longitude)}];
}

Another method to be aware of is debugDescription, called when you invoke the print-object command within the debugger. The default implementation within the NSObject class simply calls directly through to description.

18. Prefer Immutable Objects​

笔者建议大家尽量减少对象中的可变内容。在编程实践中，应该尽量把对外公布的属性设为只读，而且只在确有必要时才对外公布属性。有一些数据可能源自网络服务，它不会被修改，即使临时修改了也不会被推送到服务器。

不要把可变的 collection 作为属性公开！而应提供相关的方法。

19: Use Clear and Consistent Naming​

Follow the naming that has become standard in Objective-C to create interfaces that fit in and feel right.

Ensure that method names are concise but precise, and make their use read left to right just like a sentence.

20: Prefix Private Method Names​

When writing a class implementation, it is common to write methods that are used only internally. For such methods, I suggest that you prefix their names with something. This helps with debugging by clearly separating the public methods from the private ones.

21. Objective-C Error Model​

Use exceptions only for fatal errors that should bring down the entire application.

For nonfatal errors, either provide a delegate method to handle errors or offer an out-parameter NSError object.

22. NSCopying​

Implement the NSCopying protocol if your object will need to be copied.

浅复制（浅拷贝、指针拷贝、shallow copy）：没有产生新对象，仍然指向同一块内存空间。

  1. 源对象和副本对象是同一对象；
  2. 源对象引用计数 +1，相当于做一次 retain 操作。

深复制（深拷贝、内容拷贝、deep copy）：产生了新对象，存放在一块新的内存空间，与原来的对象互不影响。

  1. 源对象和副本对象是不同的两个对象；
  2. 源对象引用计数不变，副本对象计数为 1（因为是新产生的）。
  3. 集合的深复制只复制容器本身，集合内的元素还是原来的元素（指向同一块内存）。

img

只有源对象和副本对象都不可变时，才是浅复制，其他都是深复制。

Demo *demo1 = [[Demo alloc]init];
Demo *demo2 = [[Demo alloc]init];
NSArray *arr = @[demo1, demo2];
NSMutableArray *mutableArr = [arr mutableCopy];
NSLog(@"%p, %p", arr, mutableArr); // 集合深拷贝
NSLog(@"%p, %p", [arr objectAtIndex:0], [mutableArr objectAtIndex:0]); // 集合中的对象还是指向同一块内存