面试题：Objective-C 状态模式在复杂业务场景中的应用

设计思路

定义状态基类：创建一个基类表示订单状态，定义通用的方法，如获取当前状态描述、处理特定操作等。
创建具体状态类：继承自状态基类，针对每个订单状态（待支付、已支付、已发货、已完成、已取消）创建具体的状态类，重写基类方法来实现每个状态下的特定行为。
订单类：包含一个状态对象的引用，根据不同的操作切换状态对象，从而实现状态的转换。

核心代码片段

状态基类

#import <Foundation/Foundation.h>

// 订单状态基类
@interface OrderState : NSObject
- (NSString *)stateDescription;
- (void)handlePayment:(NSObject *)order;
- (void)handleViewLogistics:(NSObject *)order;
@end

@implementation OrderState
- (NSString *)stateDescription {
    return @"未知状态";
}
- (void)handlePayment:(NSObject *)order {
    NSLog(@"当前状态不支持支付操作");
}
- (void)handleViewLogistics:(NSObject *)order {
    NSLog(@"当前状态不支持查看物流操作");
}
@end

具体状态类 - 待支付

#import "OrderState.h"

@interface PendingPaymentState : OrderState
- (NSString *)stateDescription;
- (void)handlePayment:(NSObject *)order;
@end

@implementation PendingPaymentState
- (NSString *)stateDescription {
    return @"待支付";
}
- (void)handlePayment:(NSObject *)order {
    // 处理支付逻辑，这里简单示例状态转换
    NSLog(@"支付成功，订单状态转换为已支付");
    // 假设order有一个方法来切换状态
    [(id)order changeState:[[PaidState alloc] init]];
}
@end

具体状态类 - 已支付

#import "OrderState.h"

@interface PaidState : OrderState
- (NSString *)stateDescription;
- (void)handleViewLogistics:(NSObject *)order;
@end

@implementation PaidState
- (NSString *)stateDescription {
    return @"已支付";
}
- (void)handleViewLogistics:(NSObject *)order {
    // 这里简单示例，假设已发货才支持查看物流，先判断是否可以转换到已发货状态
    NSLog(@"订单尚未发货，暂不支持查看物流");
    // 这里可以添加逻辑判断是否可以转换到已发货状态，比如商家操作等
}
@end

具体状态类 - 已发货

#import "OrderState.h"

@interface ShippedState : OrderState
- (NSString *)stateDescription;
- (void)handleViewLogistics:(NSObject *)order;
@end

@implementation ShippedState
- (NSString *)stateDescription {
    return @"已发货";
}
- (void)handleViewLogistics:(NSObject *)order {
    NSLog(@"查看物流信息...");
}
@end

具体状态类 - 已完成

#import "OrderState.h"

@interface CompletedState : OrderState
- (NSString *)stateDescription;
@end

@implementation CompletedState
- (NSString *)stateDescription {
    return @"已完成";
}
@end

具体状态类 - 已取消

#import "OrderState.h"

@interface CancelledState : OrderState
- (NSString *)stateDescription;
@end

@implementation CancelledState
- (NSString *)stateDescription {
    return @"已取消";
}
@end

订单类

#import <Foundation/Foundation.h>
#import "OrderState.h"

@interface Order : NSObject
@property (nonatomic, strong) OrderState *currentState;

- (instancetype)initWithState:(OrderState *)state;
- (void)changeState:(OrderState *)state;
- (void)handlePayment;
- (void)handleViewLogistics;
@end

@implementation Order
- (instancetype)initWithState:(OrderState *)state {
    self = [super init];
    if (self) {
        _currentState = state;
    }
    return self;
}
- (void)changeState:(OrderState *)state {
    _currentState = state;
    NSLog(@"订单状态已转换为: %@", [_currentState stateDescription]);
}
- (void)handlePayment {
    [_currentState handlePayment:self];
}
- (void)handleViewLogistics {
    [_currentState handleViewLogistics:self];
}
@end

使用示例

#import <UIKit/UIKit.h>
#import "Order.h"
#import "PendingPaymentState.h"

int main(int argc, char * argv[]) {
    @autoreleasepool {
        Order *order = [[Order alloc] initWithState:[[PendingPaymentState alloc] init]];
        NSLog(@"当前订单状态: %@", [order.currentState stateDescription]);
        [order handlePayment];
        NSLog(@"当前订单状态: %@", [order.currentState stateDescription]);
        [order handleViewLogistics];
    }
    return 0;
}

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面试题：Objective-C 状态模式在复杂业务场景中的应用

知识考点

面试题答案

设计思路

核心代码片段

使用示例