设计模式之过滤器模式(8)

过滤器模式

过滤器模式（Filter Pattern）或标准模式（Criteria Pattern）是一种设计模式，这种模式允许开发人员使用不同的标准来过滤一组对象，通过逻辑运算以解耦的方式把它们连接起来。这种类型的设计模式属于结构型模式，它结合多个标准来获得单一标准。

实现

我们将创建一个 Person 对象、Criteria 接口和实现了该接口的实体类，来过滤 Person 对象的列表。CriteriaPatternDemo，我们的演示类使用 Criteria 对象，基于各种标准和它们的结合来过滤 Person 对象的列表。

过滤器模式的 UML 图

创建一个类，在该类上应用标准。

@interface Person_2 : NSObject
@property (nonatomic,copy,readonly) NSString *name;
@property (nonatomic,copy,readonly) NSString *gender;
@property (nonatomic,copy,readonly) NSString *maritalStatus;

- (NSString *)getName;
- (NSString *)getGender;
- (NSString *)getMaritalStatus;
- (instancetype)initWithName:(NSString *)name gender:(NSString *)gender maritalStatus:(NSString *)maritalStatus;
@end

步骤 2
为标准（Criteria）创建一个接口。

@protocol Criteria 
-(NSMutableArray *)meetCriteria:(NSMutableArray *)list;
@end

步骤 3
创建实现了 Criteria 接口的实体类。

@interface CriteriaMale : NSObject 
- (NSMutableArray *)meetCriteria:(NSMutableArray *)list;
@end
@interface CriteriaSingle : NSObject 
- (NSMutableArray *)meetCriteria:(NSMutableArray *)list;
@end
@implementation CriteriaMale

-(NSMutableArray *)meetCriteria:(NSMutableArray *)list{
    NSMutableArray *newList=[NSMutableArray array];
    for (Person_2 *item in list) {
        if ([item.getGender.uppercaseString isEqualToString:@"MALE"]) {
            [newList addObject:item];
        }
    }
    return newList;
}
@end
@implementation CriteriaSingle

-(NSMutableArray *)meetCriteria:(NSMutableArray *)list{
    NSMutableArray *newList=[NSMutableArray array];
    for (Person_2 *item in list) {
        if ([item.getMaritalStatus.lowercaseString isEqualToString:@"single"]) {
            [newList addObject:item];
        }
    }
    return newList;
}
@end

and 和or

@interface andCriteria : NSObject 

@property (nonatomic,strong) id _Nullable criteria;
@property (nonatomic,strong) id _Nullable otherCriteria;

- (NSMutableArray *)meetCriteria:(NSMutableArray *)list;

@end
@interface orCriteria : NSObject 

@property (nonatomic,strong) id _Nullable criteria;
@property (nonatomic,strong) id _Nullable otherCriteria;

- (NSMutableArray *)meetCriteria:(NSMutableArray *)list;

@end

@implementation andCriteria

- (NSMutableArray *)meetCriteria:(NSMutableArray *)list{
    NSMutableArray *newList2=[NSMutableArray array];
    [newList2 addObjectsFromArray:[self.criteria performSelector:@selector(meetCriteria:)
                                                      withObject:list]];
    return [self.otherCriteria performSelector:@selector(meetCriteria:) withObject:newList2];
}
@end
@implementation orCriteria

- (NSMutableArray *)meetCriteria:(NSMutableArray *)list{
    NSMutableArray *newList1=[NSMutableArray array];
    NSMutableArray *newList2=[NSMutableArray array];
    [newList2 addObjectsFromArray:[self.criteria performSelector:@selector(meetCriteria:)
                                                      withObject:list]];
    [newList1 addObjectsFromArray:[self.criteria performSelector:@selector(meetCriteria:)
                                                      withObject:list]];
    for (Person_2 *item in newList2) {
        if ([newList1 containsObject:item] == NO) {
            [newList1 addObject:item];
        }
    }
    return newList1;
}
@end

步骤4
使用不同的标准（Criteria）和它们的结合来过滤 Person 对象的列表。

NSMutableArray *list1 =[NSMutableArray array];
    [list1 addObject:[[Person_2 alloc]initWithName:@"Join" gender:@"Male" maritalStatus:@"single"]];
    [list1 addObject:[[Person_2 alloc]initWithName:@"Bob" gender:@"Single" maritalStatus:@"single"]];
    [list1 addObject:[[Person_2 alloc]initWithName:@"Mike" gender:@"Single" maritalStatus:@"Male"]];
    
    CriteriaMale *male=[CriteriaMale new];
    CriteriaSingle *signle=[CriteriaSingle new];
    andCriteria *and=[andCriteria new];
    orCriteria *or=[orCriteria new];
    NSLog(@"Males:%@",[male meetCriteria:list1]);
    NSLog(@"Single:%@",[signle meetCriteria:list1]);
    and.criteria = male;
    and.otherCriteria = signle;
    NSLog(@"and:%@",[and meetCriteria:list1]);
    or.criteria = male;
    or.otherCriteria = signle;
    NSLog(@"or:%@",[or meetCriteria:list1]);

步骤 5
执行程序，输出结果：

2019-05-21 17:55:31.172443+0800 test[82594:19349590] Males:(
    ""
)
2019-05-21 17:55:31.172659+0800 test[82594:19349590] Single:(
    "",
    ""
)
2019-05-21 17:55:31.172819+0800 test[82594:19349590] and:(
    ""
)
2019-05-21 17:55:31.172955+0800 test[82594:19349590] or:(
    ""
)

过滤器比较简单，就是将过滤的条件封装成抽象类，然后继承这个抽象类，可以封装各种各样的条件，最终返回想要的结果。

参考资料
runoob