ios技术面试题-白红宇

ios技术面试题

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发布时间：2019-06-23

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1.Difference between shallow copy and deep copy?

浅复制只拷贝地址不拷贝地址指向的对象

深复制拷贝地址并且指向拷贝的新对象

2.What is advantage of categories? What is difference between implementing a category and inheritance?

categories: 在不影响或修改原来的类别或模组的情况下去修改原有的功能，增加新的功能

3.Difference between categories and extensions?

categories: 在不影响或修改原来的类别或模组的情况下去修改原有的功能，增加新的功能

4.Difference between protocol in objective c and interfaces in java?

暂时觉得它们是一样的 protocol 可以被继承 interfaces 不可以

在java 中的interfaces 在 objective-c 中就是 protocol

在java 中的 class 在 objective-c 中就是 interface

5.What are KVO and KVC?

转自

一个对象拥有某些属性。比如说，一个 Person 对象有一个 name 和一个 address 属性。以 KVC 说法，Person 对象分别有一个 value 对应他的 name 和 address 的 key。 key 只是一个字符串，它对应的值可以是任意类型的对象。从最基础的层次上看，KVC 有两个方法：一个是设置 key 的值，另一个是获取 key 的值。如下面的例子：

Java代码

void changeName(Person *p, NSString *newName)

{

// using the KVC accessor (getter) method

NSString *originalName = [p valueForKey:@"name"];

// using the KVC accessor (setter) method.

[p setValue:newName forKey:@"name"];

NSLog(@"Changed %@'s name to: %@", originalName, newName);

}

现在，如果 Person 有另外一个 key 配偶（spouse），spouse 的 key 值是另一个 Person 对象，用 KVC 可以这样写：

Java代码

void logMarriage(Person *p)

{

// just using the accessor again, same as example above

NSString *personsName = [p valueForKey:@"name"];

// this line is different, because it is using

// a "key path" instead of a normal "key"

NSString *spousesName = [p valueForKeyPath:@"spouse.name"];

NSLog(@"%@ is happily married to %@", personsName, spousesName);

}

Key-Value Observing (KVO) 建立在 KVC 之上，它能够观察一个对象的 KVC key path 值的变化。举个例子，用代码观察一个 person 对象的 address 变化，以下是实现的三个方法：

watchPersonForChangeOfAddress: 实现观察

observeValueForKeyPath:ofObject:change:context: 在被观察的 key path 的值变化时调用。

dealloc 停止观察static NSString *const KVO_CONTEXT_ADDRESS_CHANGED = @"KVO_CONTEXT_ADDRESS_CHANGED"
Java代码
2. @implementation PersonWatcher
4. -(void) watchPersonForChangeOfAddress:(Person *)p
5. {
7. // this begins the observing
8. [p addObserver:self
9. forKeyPath:@"address"
10. options:0
11. context:KVO_CONTEXT_ADDRESS_CHANGED];
13. // keep a record of all the people being observed,
14. // because we need to stop observing them in dealloc
15. [m_observedPeople addObject:p];
16. }
18. // whenever an observed key path changes, this method will be called
19. - (void)observeValueForKeyPath:(NSString *)keyPath
20. ofObject:(id)object
21. change:(NSDictionary *)change
22. context:(void *)context
24. {
25. // use the context to make sure this is a change in the address,
26. // because we may also be observing other things
27. if(context == KVO_CONTEXT_ADDRESS_CHANGED) {
28. NSString *name = [object valueForKey:@"name"];
29. NSString *address = [object valueForKey:@"address"];
30. NSLog(@"%@ has a new address: %@", name, address);
31. }
32. }
34. -(void) dealloc;
35. {
37. // must stop observing everything before this object is
38. // deallocated, otherwise it will cause crashes
39. for(Person *p in m_observedPeople){
40. [p removeObserver:self forKeyPath:@"address"];
41. }
43. [m_observedPeople release];
44. m_observedPeople = nil;
46. [super dealloc];
48. }
50. -(id) init;
51. {
52. if(self = [super init]){
53. m_observedPeople = [NSMutableArray new];
54. }
56. return self;
57. }
59. @end
这就是 KVO 的作用，它通过 key path 观察对象的值，当值发生变化的时候会收到通知。