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完全参照 命令模式|菜鸟教程但不包括IOS代码
命令模式
命令模式(Command Pattern)是一种数据驱动的设计模式,它属于行为型模式。请求以命令的形式包裹在对象中,并传给调用对象。调用对象寻找可以处理该命令的合适的对象,并把该命令传给相应的对象,该对象执行命令。
介绍
意图: 将一个请求封装成一个对象,从而使您可以用不同的请求对客户进行参数化。
主要解决: 在软件系统中,行为请求者与行为实现者通常是一种紧耦合的关系,但某些场合,比如需要对行为进行记录、撤销或重做、事务等处理时,这种无法抵御变化的紧耦合的设计就不太合适。
何时使用:在某些场合,比如要对行为进行"记录、撤销/重做、事务"等处理,这种无法抵御变化的紧耦合是不合适的。在这种情况下,如何将"行为请求者"与"行为实现者"解耦?将一组行为抽象为对象,可以实现二者之间的松耦合。
如何解决: 通过调用者调用接受者执行命令,顺序:调用者→接受者→命令。
关键代码: 定义三个角色:1、received 真正的命令执行对象 2、Command 3、invoker 使用命令对象的入口
应用实例:struts 1 中的 action 核心控制器 ActionServlet 只有一个,相当于 Invoker,而模型层的类会随着不同的应用有不同的模型类,相当于具体的 Command。
优点:
1、降低了系统耦合度。
2、新的命令可以很容易添加到系统中去。
缺点: 使用命令模式可能会导致某些系统有过多的具体命令类。
使用场景: 认为是命令的地方都可以使用命令模式,比如:
1、GUI 中每一个按钮都是一条命令。
2、模拟 CMD。
注意事项: 系统需要支持命令的撤销(Undo)操作和恢复(Redo)操作,也可以考虑使用命令模式,见命令模式的扩展。
Android
Order.java
public interface Order {
void execute();
}
Stock.java
public class Stock {
private String name = "ABC";
private int quantity = 10;
public void buy(){
System.out.println("Stock [ Name: "+name+",
Quantity: " + quantity +" ] bought");
}
public void sell(){
System.out.println("Stock [ Name: "+name+",
Quantity: " + quantity +" ] sold");
}
}
BuyStock.java
public class BuyStock implements Order {
private Stock abcStock;
public BuyStock(Stock abcStock){
this.abcStock = abcStock;
}
public void execute() {
abcStock.buy();
}
}
SellSto
SellStock.java
public class SellStock implements Order {
private Stock abcStock;
public SellStock(Stock abcStock){
this.abcStock = abcStock;
}
public void execute() {
abcStock.sell();
}
}
Broker.java
import java.util.ArrayList;
import java.util.List;
public class Broker {
private List<Order> orderList = new ArrayList<Order>();
public void takeOrder(Order order){
orderList.add(order);
}
public void placeOrders(){
for (Order order : orderList) {
order.execute();
}
orderList.clear();
}
}
CommandPatternDemo.java
public class CommandPatternDemo {
public static void main(String[] args) {
Stock abcStock = new Stock();
BuyStock buyStockOrder = new BuyStock(abcStock);
SellStock sellStockOrder = new SellStock(abcStock);
Broker broker = new Broker();
broker.takeOrder(buyStockOrder);
broker.takeOrder(sellStockOrder);
broker.placeOrders();
}
}
结果
Stock [ Name: ABC, Quantity: 10 ] bought
Stock [ Name: ABC, Quantity: 10 ] sold
IOS
Order.h
#import <Foundation/Foundation.h>
#import "Stock.h"
@interface Order : NSObject
-(void)execute;
@end
@interface BuyStock : Order
-(instancetype)initWithStock:(Stock*)abcStock;
@end
@interface SellStock : Order
-(instancetype)initWithStock:(Stock*)abcStock;
@end
Order.m
#import "Order.h"
@implementation Order
- (void)execute{}
@end
@interface BuyStock ()
@property (nonatomic, strong) Stock * abcStock;
@end
@implementation BuyStock
- (instancetype)initWithStock:(Stock *)abcStock{
if(self = [super init]) {
self.abcStock = abcStock;
}
return self;
}
- (void)execute{
if(self.abcStock) {
[self.abcStock buy];
}
}
@end
@interface SellStock ()
@property (nonatomic, strong) Stock * abcStock;
@end
@implementation SellStock
- (instancetype)initWithStock:(Stock *)abcStock{
if(self = [super init]) {
self.abcStock = abcStock;
}
return self;
}
- (void)execute{
if(self.abcStock) {
[self.abcStock sell];
}
}
@end
Stock.h
#import <Foundation/Foundation.h>
@interface Stock : NSObject
-(void)buy;
-(void)sell;
@end
Stock.m
#import "Stock.h"
@interface Stock ()
@property (nonatomic, strong) NSString* name;
@property (nonatomic, assign) int quantity;
@end
@implementation Stock
- (NSString *)name{
return @"ABC";
}
- (int)quantity{
return 10;
}
- (void)buy{
NSLog(@"Stock [ Name: %@, Quantity:%d ] bought", self.name, self.quantity);
}
- (void)sell{
NSLog(@"Stock [ Name: %@, Quantity:%d ] sold", self.name, self.quantity);
}
@end
Broker.h
#import <Foundation/Foundation.h>
#import "Order.h"
@interface Broker : NSObject
-(void)takeOrder:(Order*)order;
-(void)placeOrders;
@end
Broker.m
#import "Broker.h"
@interface Broker ()
@property (nonatomic ,strong) NSMutableArray * orderList;
@end
@implementation Broker
- (NSMutableArray *)orderList{
if(!_orderList) {
_orderList = [[NSMutableArray alloc]init];
}
return _orderList;
}
-(void)takeOrder:(Order*)order{
[self.orderList addObject:order];
}
-(void)placeOrders{
for (Order *order in self.orderList) {
[order execute];
}
[self.orderList removeAllObjects];
}
@end
ViewController
- (void)viewDidLoad {
[super viewDidLoad];
Stock *abcStock = Stock.new;
BuyStock *buyStockOrder = [[BuyStock alloc]initWithStock:abcStock];
SellStock *sellStockOrder = [[SellStock alloc] initWithStock:abcStock];
Broker *broker = Broker.new;
[broker takeOrder:buyStockOrder];
[broker takeOrder:sellStockOrder];
[broker placeOrders];
}
结果
Stock [ Name: ABC, Quantity:10 ] bought
Stock [ Name: ABC, Quantity:10 ] sold