formula , It’s just convenient to remember ：
The original work order is
Bridge agent composition adapter , Enjoy yuan’s decorative appearance
Visitors write strategy memos , Observe the state of the template iteration , Order the intermediary to explain the chain of responsibility .
Many design patterns ,GOF Just list it 23 Kind of , This paper only gives three examples .
1.1.1 Factory method
Defines an interface for creating objects , Let the subclass decide which class to instantiate . Customize a message box , Initially, you can only set the title and content . later ： You can choose whether there are buttons , Is there an icon . Stupid way ：4 Two classes correspond to 4 In this case . The simplest solution ： Add two member variables to record relevant information . later ： Icons can be changed , And the number is variable ; Click a button and the dialog doesn’t need to close . Feasible solution , Two factory method modes and one bridge mode ： Two virtual functions are added to the message box class ： Create button groups and icon groups . It is implemented by derived classes .
1.1.2 Decoration mode
Dynamically add some additional responsibilities to an object . Suppose a company defines a class level interface ： Show logo, There’s only one function level interface ： Show . Suppose Weibo 、 Blog 、 The forum supports this interface , Several developers have implemented different ways of display logo, such as ： Text logo、 picture logo、 Reverse text logo. One developer wants to add copyright , Support already exists 、 There is no indication of logo The way . Define a class “ Display copyright logo” Realization “ Show logo” Interface , Constructors have arguments “ Basic display logo”, Show logo when ： First call “ Basic display logo” Display of , Then show the copyright in the lower right corner .
1.1.3 Visitor mode
Represents an operation on each element of an object structure . It allows you to do this without changing the classes of the elements
Define new operations that act on these elements . some CAD, There are image interface classes , This interface has two functions ： Find the area and perimeter . A developer wants to add an unusual operation ： Seeking the center .CAD It’s impossible to add unusual operations . If CAD Developers use visitor mode , There would be no such problem . Let’s assume that there are limited kinds of figures , The following source code only rectangle and circle ; Let’s assume that the calculation is infinite , This source code only ： Find the area 、 Perimeter . It’s not convenient to dictate , Code up ：