NSSortDescriptor:Array,Set和Core Data中排序的实现

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NSSortDescriptor 是重要的排序类, 可以非常方便滴对一些集合类进行排序, 在core data中使用也非常的广泛.

初始化方法

+ (instancetype)sortDescriptorWithKey:(NSString *)key ascending:(BOOL)ascending NS_AVAILABLE(10_6, 4_0);+ (instancetype)sortDescriptorWithKey:(NSString *)key ascending:(BOOL)ascending selector:(SEL)selector NS_AVAILABLE(10_6, 4_0);<pre name="code" class="objc">+ (instancetype)sortDescriptorWithKey:(NSString *)key ascending:(BOOL)ascending comparator:(NSComparator)cmptr NS_AVAILABLE(10_6, 4_0);

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

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

三个参数是:

Key: 排序的key 或者 keyPath

ascending: YES 升序 NO 降序

比较参数: selector 或者 NSComparator

selector 的例子说明: selector指定了一个key属性的类型实现的方法,传进来一个值和本身(self)对比,返回一个NSComparisonResult结果

- (NSComparisonResult)localizedCompare:(NSString *)aString

typedef NSComparisonResult (^NSComparator)(id obj1, id obj2)是个block , 传入两个对象, 返回一个NSComparisonResult结果

例子,有一个书类,有三个属性

@interface Book : NSObject@property (nonatomic, copy) NSString *name;@property (nonatomic, copy) NSString *author;@property (nonatomic, assign) float price;@end

初始化数据

    Book *book = [[Book alloc] init];    [book setValue:@"iOS开发" forKey:@"name"];    [book setValue:@"张三" forKey:@"author"];    [book setValue:@99.0 forKey:@"price"];        Book *book2 = [[Book alloc] init];    [book2 setValue:@"Android开发" forKey:@"name"];    [book2 setValue:@"李四" forKey:@"author"];    [book2 setValue:@79.0 forKey:@"price"];        Book *book3 = [[Book alloc] init];    [book3 setValue:@"PHP开发" forKey:@"name"];    [book3 setValue:@"王五" forKey:@"author"];    [book3 setValue:@59.0 forKey:@"price"];    Book *book4 = [[Book alloc] init];    [book4 setValue:@"HTML开发" forKey:@"name"];    [book4 setValue:@"赵六" forKey:@"author"];    [book4 setValue:@99.0 forKey:@"price"];        _bookArray = @[book, book2, book3, book4];

排序

    //价格降序排列: 规则就是---是否降序 加上 comparator比较返回的结果和比较的值是一致的 的与否 === 确定最后是降序还是升序    //降序的时候: 后面如果obj1 > obj2 就返回 NSOrderedDescending 降序    //降序的时候: 后面如果obj1 > obj2 就返回 NSOrderedAscending  升序    //升序的时候: 后面如果obj1 > obj2 就返回 NSOrderedAscending  升序    //升序的时候: 后面如果obj1 > obj2 就返回 NSOrderedDescending 降序    NSSortDescriptor *priceSort = [NSSortDescriptor sortDescriptorWithKey:@"price" ascending:NO comparator:^NSComparisonResult(id obj1, id obj2) {        float value1 = [obj1 floatValue];        float value2 = [obj2 floatValue];        if (value1 == value2) {            return NSOrderedSame;        } else if (value1 > value2) { //value1比value2大则            return NSOrderedDescending;        } else {            return NSOrderedAscending;        }    }];    //书名升序排列    NSSortDescriptor *nameSort = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(localizedStandardCompare:)];        //两者组合,共同组成排序的结果    NSArray *newArray = [_bookArray sortedArrayUsingDescriptors:@[priceSort,nameSort]];    NSLog(@"_bookArray = %@",newArray); //book4, book, book2, book3

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