设计模式学习笔记

待我称王封你为后i 2022-03-10 03:12 216阅读 0赞

three main milestones in our design process:

Conceptualizing the ideas

Designing the look-and-feel

Architectural design

Tips:

Subclassing is *white-box reuse*

Object composition is  *black-box reuse*

准则:

Program to an interface, not an implementation

模块间以protocal或基本抽象类通信..以达到最大化复用

Object Creation

1.  Prototype Pattern: 带clone方法的对象 …可以不同的class..以protocol统一clone接口

2.  Factory method Pattern: 返回抽象类型 id<…> 或含默认实现的abstract class类型..

![82bc095b-66cc-4198-9237-00ef8b34e476.png_resizeSmall_width_1024][]

用一个Abstract Factory Class ..让后来派生的factory 去重载factory method

3. Abstract  Factory Pattern:

Factory Method pattern that is used for generating concrete subclasses by an abstract class

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如 NSNumber 的 numberWith\* 方法…是factory method..并且返回的是NSNumber的各种subType ![124d9116-f4a4-4050-8175-9a0548ec4acd.png_resizeSmall_width_1024][]

Class Clusters are a form of Abstract Factory

There is a distinction between factory methods for creating abstract products and factory methods for creating abstract factories. Obviously, factory methods like intValue and boolValue should be overridden in concrete factories (NSCFNumber and NSCFBoolean) to return actual values (products). Other factory methods like numberWithBool: and numberWithInt: are not for returning products but for returning actual factories that return products. They are not intended to be overridden in concrete factory subclasses.

4. Builder Pattern: Separates the construction of a complex object from its representation so that the same construction process can create different representations

client- >director->builder -> product

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5. Singleton Pattern:  Ensures a class has only one instance, and provide a global point of access to it

we can use some Foundation functions to instantiate whatever object based on its class type. One of them is id NSAllocateObject (Class aClass, NSUInteger extraBytes, NSZone \*zone). So if we want to instantiate an object of a class called “Singleton,” we can do the following:

Singleton \*singleton = \[NSAllocateObject (\[Singleton class\], 0, NULL) init\];

Interface Adaptation

6. Adapter Pattern: 没有某operation, 直接叫某个 特定的 obj间接提供

class adapter:

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object adapter:

Since it’s a “has a” relationship between Adapter and Adaptee, Adapter can adapt subclasses of Adaptee without much problem.

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the delegate object is a adapter object

7. Bridge  Pattern: 没有某operation, 叫某种<xx>对象间接提供

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8. Facade  Pattern:  Provides a unified interface to a set of interfaces in a system. Façade defines a higher-level interface that makes the subsystem easier to use

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Decoupling of Objects

9. Mediator  Pattern:  Mediator pattern is very useful for situations where the application’s behavior is distributed among different objects and they depend on each other

controller

10. Observer  Pattern:  Defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically

KVO的方式:

![b2d60138-17a8-4745-91b6-7f8ba02aa249.png_resizeSmall_width_1024][]

Notification 是center 转发式

Abstract Collection

11. Composite  Pattern:  将相同type的对象组合成树形结构以表示“部分-整体”的层次结构。它使得客户对单个对象和复合对象的使用具有一致性。

![9044393d-805b-4ae2-a395-91b83a7b6609.png_resizeSmall_width_1024][]

New operations applied on the structure can be used with the Visitor pattern (Chapter 17) to have visitors “visit” each node for further processing without modifying the existing composite structure.

12. Iterator  Pattern:  Provide a way to access to the elements of an aggregate object sequentially without exposing its underlying representation

![cd8c01a4-db7c-440a-a9d6-d5bc9b2e140d.png_resizeSmall_width_1024][]

Behavioral Extension

13. Visitor  Pattern:  The Visitor pattern represents an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates

define any external behavior that can be applied to a composite structure as a “visitor.” Visitors “visit” each node in a complex structure to perform particular operations based on the actual type of a visited node. vistitor对象负责visit compostite object中的各元素

element对象在定义时, 需要预先定义visitor接口, 并含默认实现( 遍历结点 )

与 Iterator  Pattern的遍历不同的是:  Visitor 遍历轨迹跟内部结构及结点具体类型有关(不同的实例结点调用不到的visit方法)…. Iterator 只是按抽象基类简单地遍历

![d37c795c-bf95-4c0d-959b-a4c584d4cce8.png_resizeSmall_width_1024][]

14. Decorator  Pattern:

Decorator 和 component 的接口是一致的

proxy跟decorator的区别就是..前者是为了限制等..后者为了扩展?

![411f75ff-ce06-4f0c-8f17-b907e7309b32.png_resizeSmall_width_1024][]

true subclass approach: 结构同上图, 可以成链

category:

15. Chain of responsibility  Pattern:  To avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. It chains the receiving objects and passes the request along the chain until an object handles it

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Algorithm Encapsulation

16. Template Method  Pattern:  Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure

![863d0987-9455-432b-b7d6-554e519005c4.png_resizeSmall_width_1024][]

17. Strategy  Pattern:  Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

只封装action

![466dca9d-383d-4e93-9e37-14e2c7ac5fac.png_resizeSmall_width_1024][]

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18. Command pattern: 封装的是request..即 \[target action\]

target …action均可配置

统一命令接口, 不同的命令派生不同的类, 每一份实例接受变化的入参而重复使用之

Executed command objects can be collected and queued as a list of command history

undo…redo

![b9e1bf68-9cec-4229-8b0f-a6d6ecf804ac.png_resizeSmall_width_1024][]

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NSundoManager doesn’t retain its invocation target receivers,

Performance and Object Access

19. Flyweight pattern:  Uses sharing to support large numbers of fine-grained objects efficiently

抽出决定 unique 的 extrinsic 元素..剩余的 intrinsic 共享之

UITableViewCell 就是如此复用的

![9e0efcbc-ba91-48d4-8952-b4390a61863e.png_resizeSmall_width_1024][]

20.  Proxy pattern :  Provides a surrogate or placeholder for another object to control access to it.

In general, a proxy acts as a surrogate or placeholder that controls access to another object, objects that are remote, expensive to create, or in need of securing.

![df8b5064-2bd0-4d9f-90eb-aa4eccb7a975.png_resizeSmall_width_1024][]

virtual proxy: 提供与被代理对象同样的接口, 使得自身表现得跟被代理对象一样. 同时又加入一些扩展方法…通过用继承的方式实现..

如JCAsynImageView 就是UIIamgeView 的 proxy

proxy跟decorator的区别就是..前者是为了限制等..后者为了扩展?

Objective-C doesn’t support multiple inheritances. So if your proxy objects are not subclasses of anything specific in the Cocoa Touch framework, you may consider using NSProxy for your placeholders or surrogate objects.

State of Object

21. Memento  pattern :  Without violating encapsulation, capture and externalize an object’s internal state so that the object can be restored to this state later

取原来复杂类的一个简单必要子集作为一个memento class.

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