[iOS] 浅析排序规则描述类: NSSortDescriptor

转载自：https://www.jianshu.com/p/3e9f0884be6b

NSSortDescriptor是用来指定排序规则, 对集合等进行排序时指定结果的排序规则;
他可以对一个类的某个属性(下文中方法中的key参数)指定排序规则, 也可以对一个字符串集合进行指定排序规则, 这时, 只需要把参数key赋值为nil即可.
iOS中的集合都有相应的扩展方法来使用NSSortDescriptor:

NSSet

-(NSArray<ObjectType> *)sortedArrayUsingDescriptors:(NSArray<NSSortDescriptor *> *)sortDescriptors

NSArray

-(NSArray<ObjectType> *)sortedArrayUsingDescriptors:(NSArray<NSSortDescriptor *> *)sortDescriptors;

NSMutableArray

-(void)sortUsingDescriptors:(NSArray<NSSortDescriptor *> *)sortDescriptors;

NSOrderedSet

-(NSArray<ObjectType> *)sortedArrayUsingDescriptors:(NSArray<NSSortDescriptor *> *)sortDescriptors

NSMutableOrderedSet

-(void)sortUsingDescriptors:(NSArray<NSSortDescriptor *> *)sortDescriptors

上面的参数都是包含NSSortDescriptor的数组, 意思是说可以同时指定多条规则来进行排序, 其优先级取决于在数组中的先后顺序;

初始化方法

初始化方法有以下几种:

+ (instancetype)sortDescriptorWithKey:(nullable NSString *)key ascending:(BOOL)ascending NS_AVAILABLE(10_6, 4_0);
+ (instancetype)sortDescriptorWithKey:(nullable NSString *)key ascending:(BOOL)ascending selector:(nullable SEL)selector NS_AVAILABLE(10_6, 4_0);

// keys may be key paths
- (instancetype)initWithKey:(nullable NSString *)key ascending:(BOOL)ascending;
- (instancetype)initWithKey:(nullable NSString *)key ascending:(BOOL)ascending selector:(nullable SEL)selector;

+ (instancetype)sortDescriptorWithKey:(nullable NSString *)key ascending:(BOOL)ascending comparator:(NSComparator)cmptr NS_AVAILABLE(10_6, 4_0);
- (instancetype)initWithKey:(nullable NSString *)key ascending:(BOOL)ascending comparator:(NSComparator)cmptr NS_AVAILABLE(10_6, 4_0);

下面通过一个示例来说明各个方法的使用规则:

创建假数据

这里定义了一个简单model:

// People.h
@interface People : NSObject

@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) BOOL sex;
@property (nonatomic, assign) double height;
@property (nonatomic, assign) int age;
@end

// People.m
@implementation People
@end

生成假数据:

 NSArray *names = @[@"夏侯惇", @"貂蝉", @"诸葛亮", @"张三", @"李四", @"流火绯瞳", @"流火", @"李白", @"张飞", @"韩信", @"范冰冰", @"赵丽颖"];
 NSArray *ages = @[@32, @32, @45, @32, @32, @27, @15, @67, @55, @34, @44, @30];
 NSArray *heights = @[@170, @163, @180, @165, @163, @176, @174, @183, @186, @178, @167, @160];
    
    NSMutableArray *peoples = [NSMutableArray arrayWithCapacity:names.count];
    for (int i = 0; i<names.count; i++) {
        
        People *pe = [[People alloc]init];
        pe.name = names[i];
        pe.age = [ages[i] intValue];
        pe.height = [heights[i] doubleValue];
        [peoples addObject:pe];
    }

以下示例代码, 都是对这个peoples数组进行操作

+ (instancetype)sortDescriptorWithKey:(nullable NSString *)key ascending:(BOOL)ascending

- (instancetype)initWithKey:(nullable NSString *)key ascending:(BOOL)ascending

参数
key : 排序key, 某个对象的属性名称; 如果对字符串进行排序, 则传nil
ascending : 是否升序, YES-升序, NO-降序

示例代码:

NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"age" ascending:YES];
   
 [peoples sortUsingDescriptors:@[sort]];
    
    // 输出排序结果
    for (People *people in peoples) {
        NSLog(@"age: %d,height: %f name: %@", people.age,people.height, people.name);
    }

输出:

2017-06-30 16:25:39.628 NSPredicateTest[10794:419605] age: 15,height: 174.0 name: 流火
2017-06-30 16:25:39.629 NSPredicateTest[10794:419605] age: 27,height: 176.0 name: 流火绯瞳
2017-06-30 16:25:39.630 NSPredicateTest[10794:419605] age: 30,height: 160.0 name: 赵丽颖
2017-06-30 16:25:39.630 NSPredicateTest[10794:419605] age: 32,height: 170.0 name: 夏侯惇
2017-06-30 16:25:39.631 NSPredicateTest[10794:419605] age: 32,height: 163.0 name: 貂蝉
2017-06-30 16:25:39.631 NSPredicateTest[10794:419605] age: 32,height: 165.0 name: 张三
2017-06-30 16:25:39.631 NSPredicateTest[10794:419605] age: 32,height: 163.0 name: 李四
2017-06-30 16:25:39.631 NSPredicateTest[10794:419605] age: 34,height: 178.0 name: 韩信
2017-06-30 16:25:39.632 NSPredicateTest[10794:419605] age: 44,height: 167.0 name: 范冰冰
2017-06-30 16:25:39.632 NSPredicateTest[10794:419605] age: 45,height: 180.0 name: 诸葛亮
2017-06-30 16:25:39.632 NSPredicateTest[10794:419605] age: 55,height: 186.0 name: 张飞
2017-06-30 16:25:39.632 NSPredicateTest[10794:419605] age: 67,height: 183.0 name: 李白

也可以同时指定多个规则: 按年龄升序排列, 相同的再按身高降序排列:

NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"age" ascending:YES];
NSSortDescriptor *sort1 = [NSSortDescriptor sortDescriptorWithKey:@"height" ascending:NO];
[peoples sortUsingDescriptors:@[sort, sort1]];
    
    // 输出排序结果
    for (People *people in peoples) {
        NSLog(@"age: %d,height: %.1f name: %@", people.age,people.height, people.name);
    }

输出:

2017-06-30 16:27:27.489 NSPredicateTest[10856:421571] age: 15,height: 174.0 name: 流火
2017-06-30 16:27:27.490 NSPredicateTest[10856:421571] age: 27,height: 176.0 name: 流火绯瞳
2017-06-30 16:27:27.490 NSPredicateTest[10856:421571] age: 30,height: 160.0 name: 赵丽颖
2017-06-30 16:27:27.490 NSPredicateTest[10856:421571] age: 32,height: 170.0 name: 夏侯惇
2017-06-30 16:27:27.490 NSPredicateTest[10856:421571] age: 32,height: 165.0 name: 张三
2017-06-30 16:27:27.490 NSPredicateTest[10856:421571] age: 32,height: 163.0 name: 貂蝉
2017-06-30 16:27:27.490 NSPredicateTest[10856:421571] age: 32,height: 163.0 name: 李四
2017-06-30 16:27:27.491 NSPredicateTest[10856:421571] age: 34,height: 178.0 name: 韩信
2017-06-30 16:27:27.491 NSPredicateTest[10856:421571] age: 44,height: 167.0 name: 范冰冰
2017-06-30 16:27:27.491 NSPredicateTest[10856:421571] age: 45,height: 180.0 name: 诸葛亮
2017-06-30 16:27:27.491 NSPredicateTest[10856:421571] age: 55,height: 186.0 name: 张飞
2017-06-30 16:27:27.491 NSPredicateTest[10856:421571] age: 67,height: 183.0 name: 李白

这次主要是看年龄为32的排列顺序;

+ (instancetype)sortDescriptorWithKey:(nullable NSString *)key ascending:(BOOL)ascending selector:(nullable SEL)selector

- (instancetype)initWithKey:(nullable NSString *)key ascending:(BOOL)ascending selector:(nullable SEL)selector

参数:
key : 排序key, 某个对象的属性名称
ascending : 是否升序, YES-升序, NO-降序
selector : 自定义排序规则, 如果需要自己定义排序规则, 可传递此方法, 这个使用相对比较复杂; 如果待比较的属性是字符串(NSString)类型, 可使用其默认的方法: localizedStandardCompare:
即:

NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(localizedStandardCompare:)];

如果是其他的类型, 比如int, double等, 就需要对其类别(基本类型要对NSNumber)进行扩展;

假设还按年龄进行排序, 只不过我想修改其排序方法: ascending 为YES时, 让其降序排列(本应该是升序排列), 可以这样做:

首先, 对NSNumber类型写一个类目:

// NSNumber+mySort.h
@interface NSNumber (mySort)

- (NSComparisonResult)mySort:(NSNumber *)num;
@end

// NSNumber+mySort.m
@implementation NSNumber (mySort)
- (NSComparisonResult)mySort:(NSNumber *)num {
    
    if (self == num) {
        return NSOrderedSame;
    } else if (self > num) {
        // 当自身大于num时, 本应该返回 NSOrderedDescending , 这里反转其结果, 使返回 NSOrderedAscending
        return NSOrderedAscending;
    }else {
        return NSOrderedDescending;
    }
}
@end

然后使用:

NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"age" ascending:YES selector:@selector(mySort:)];
    
    [peoples sortUsingDescriptors:@[sort]];
    
    // 输出排序结果
    for (People *people in peoples) {
        NSLog(@"age: %d,height: %.1f name: %@", people.age,people.height, people.name);
    }

这时输出的结果就和上面相反了:

2017-06-30 16:47:44.192 NSPredicateTest[11287:445115] age: 67,height: 183.0 name: 李白
2017-06-30 16:47:44.192 NSPredicateTest[11287:445115] age: 55,height: 186.0 name: 张飞
2017-06-30 16:47:44.193 NSPredicateTest[11287:445115] age: 45,height: 180.0 name: 诸葛亮
2017-06-30 16:47:44.193 NSPredicateTest[11287:445115] age: 44,height: 167.0 name: 范冰冰
2017-06-30 16:47:44.193 NSPredicateTest[11287:445115] age: 34,height: 178.0 name: 韩信
2017-06-30 16:47:44.193 NSPredicateTest[11287:445115] age: 32,height: 170.0 name: 夏侯惇
2017-06-30 16:47:44.193 NSPredicateTest[11287:445115] age: 32,height: 163.0 name: 貂蝉
2017-06-30 16:47:44.193 NSPredicateTest[11287:445115] age: 32,height: 165.0 name: 张三
2017-06-30 16:47:44.193 NSPredicateTest[11287:445115] age: 32,height: 163.0 name: 李四
2017-06-30 16:47:44.194 NSPredicateTest[11287:445115] age: 30,height: 160.0 name: 赵丽颖
2017-06-30 16:47:44.194 NSPredicateTest[11287:445115] age: 27,height: 176.0 name: 流火绯瞳
2017-06-30 16:47:44.194 NSPredicateTest[11287:445115] age: 15,height: 174.0 name: 流火

如果是其他类型的属性, 可以分别进行扩展, 自定义排序规则, 需要注意的是, 自定义方法的返回值一定要是NSComparisonResult.

+ (instancetype)sortDescriptorWithKey:(nullable NSString *)key ascending:(BOOL)ascending comparator:(NSComparator)cmptr

- (instancetype)initWithKey:(nullable NSString *)key ascending:(BOOL)ascending comparator:(NSComparator)cmptr

参数:
key : 排序key, 某个对象的属性名称
ascending : 是否升序, YES-升序, NO-降序
cmptr: 一个block, 可以在其中指定比较规则

这里的初始化方法, 和上面的方法功能一样, 可以自己提供一个排序规则, 只不过方式不同; 这个相对于上面的方法, 在自定义排序方法不需要新建扩展, 相对方便一些:

示例:

 NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"age" ascending:YES comparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
        
        if (obj1 == obj2) {
            return NSOrderedSame;
        } else if (obj1 > obj2){
            // 当obj1大于obj2时, 本应该返回 NSOrderedDescending , 这里反转其结果, 使返回 NSOrderedAscending
            return NSOrderedAscending;
        } else {
            return NSOrderedDescending;
        }
    }];
    
    [peoples sortUsingDescriptors:@[sort]];
    
    // 输出排序结果
    for (People *people in peoples) {
        NSLog(@"age: %d,height: %.1f name: %@", people.age,people.height, people.name);
    }

这样的结果和上面是一样的:

2017-06-30 16:55:22.049 NSPredicateTest[11432:452683] age: 67,height: 183.0 name: 李白
2017-06-30 16:55:22.050 NSPredicateTest[11432:452683] age: 55,height: 186.0 name: 张飞
2017-06-30 16:55:22.050 NSPredicateTest[11432:452683] age: 45,height: 180.0 name: 诸葛亮
2017-06-30 16:55:22.050 NSPredicateTest[11432:452683] age: 44,height: 167.0 name: 范冰冰
2017-06-30 16:55:22.050 NSPredicateTest[11432:452683] age: 34,height: 178.0 name: 韩信
2017-06-30 16:55:22.050 NSPredicateTest[11432:452683] age: 32,height: 170.0 name: 夏侯惇
2017-06-30 16:55:22.051 NSPredicateTest[11432:452683] age: 32,height: 163.0 name: 貂蝉
2017-06-30 16:55:22.051 NSPredicateTest[11432:452683] age: 32,height: 165.0 name: 张三
2017-06-30 16:55:22.051 NSPredicateTest[11432:452683] age: 32,height: 163.0 name: 李四
2017-06-30 16:55:22.051 NSPredicateTest[11432:452683] age: 30,height: 160.0 name: 赵丽颖
2017-06-30 16:55:22.051 NSPredicateTest[11432:452683] age: 27,height: 176.0 name: 流火绯瞳
2017-06-30 16:55:22.051 NSPredicateTest[11432:452683] age: 15,height: 174.0 name: 流火

以上便是其初始化方法的使用规则.

如果想得到相反的结果, 达到和上面相同的效果, 还有一个方法, 就是自定义MYSortDescriptor继承自NSSortDescriptor, 重写方法:

- (NSComparisonResult)compareObject:(id)object1 toObject:(id)object2;    // primitive - override this method if you want to perform comparisons differently (not key based for example)

例如:

// MYSortDescriptor.h
@interface MYSortDescriptor : NSSortDescriptor

@end

// MYSortDescriptor.m
@implementation MYSortDescriptor

- (NSComparisonResult)compareObject:(id)object1 toObject:(id)object2 {
    // 这里反转其比较顺序
    return [super compareObject:object2 toObject:object1];
}
@end

使用:

MYSortDescriptor *sort = [MYSortDescriptor sortDescriptorWithKey:@"age" ascending:YES];

    [peoples sortUsingDescriptors:@[sort]];
    
    // 输出排序结果
    for (People *people in peoples) {
        NSLog(@"age: %d,height: %.1f name: %@", people.age,people.height, people.name);
    }

其结果, 和上面一样, 不过这个方法不常用, 上面的方法已经能够满足日常所需.

以上便是本人对 NSSortDescriptor 的学习总结, 如有不到之处, 还请指正!

[iOS] 浅析排序规则描述类: NSSortDescriptor

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