移動開發之設計模式- 命令模式(IOS&Android)
阿新 • • 發佈:2018-12-20
資源
完全參照 命令模式|菜鳥教程但不包括IOS程式碼
命令模式
命令模式(Command Pattern)是一種資料驅動的設計模式,它屬於行為型模式。請求以命令的形式包裹在物件中,並傳給呼叫物件。呼叫物件尋找可以處理該命令的合適的物件,並把該命令傳給相應的物件,該物件執行命令。
介紹
意圖: 將一個請求封裝成一個物件,從而使您可以用不同的請求對客戶進行引數化。
主要解決: 在軟體系統中,行為請求者與行為實現者通常是一種緊耦合的關係,但某些場合,比如需要對行為進行記錄、撤銷或重做、事務等處理時,這種無法抵禦變化的緊耦合的設計就不太合適。
何時使用:在某些場合,比如要對行為進行"記錄、撤銷/重做、事務"等處理,這種無法抵禦變化的緊耦合是不合適的。在這種情況下,如何將"行為請求者"與"行為實現者"解耦?將一組行為抽象為物件,可以實現二者之間的鬆耦合。
如何解決:
關鍵程式碼: 定義三個角色:1、received 真正的命令執行物件 2、Command 3、invoker 使用命令物件的入口
應用例項:struts 1 中的 action 核心控制器 ActionServlet 只有一個,相當於 Invoker,而模型層的類會隨著不同的應用有不同的模型類,相當於具體的 Command。
優點:
1、降低了系統耦合度。
2、新的命令可以很容易新增到系統中去。
缺點: 使用命令模式可能會導致某些系統有過多的具體命令類。
使用場景: 認為是命令的地方都可以使用命令模式,比如:
1、GUI 中每一個按鈕都是一條命令。
2、模擬 CMD。
注意事項: 系統需要支援命令的撤銷(Undo)操作和恢復(Redo)操作,也可以考慮使用命令模式,見命令模式的擴充套件。
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();
}
}
結果
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];
}
結果
Stock [ Name: ABC, Quantity:10 ] bought
Stock [ Name: ABC, Quantity:10 ] sold