NSArray 与 NSMutableArray 的排序

　　由于集合的使用过程中，经常需要对数组进行排序操作，此博客用于总结对在OC中对数组排序的几种方法

1.当数组中存放的是Foundation框架中提供的对象时，直接使用 compare:方法

  如：NSString、NSMutableSting等

　

        //使用块对数组排序
        NSArray* arr = @[@"4",@"3",@"1",@"2"];
        NSMutableArray* mutArr = [arr mutableCopy];
        
        //可变数组使用块 sortUsingComparator
        [mutArr sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
            return [obj1 compare: obj2];
        }];
        //不可变数组使用Comparator排序
        NSArray* sorted = [arr sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
            return [obj2 compare: obj1];
        }];
        
        NSLog(@"%@", sorted);
         NSLog(@"%@", mutArr);

        //使用块对数组进行排序
        //可变数组使用selector排序
        NSLog(@"%@", [arr sortedArrayUsingSelector:@selector(compare:)]);

2. 当数组中存放的是自定义对象时，需要自己写排序方法，或使用NSSortDescriptor进行排序

举个例子，自定义一个Student类，生成很多Student对象，放入数组中，对数组进行排序。

   2.1 Student类

#import <Foundation/Foundation.h>
@class Grade;
@interface Student : NSObject
@property (copy, nonatomic) NSString* name;
@property (assign, nonatomic) NSInteger age;
@property (copy, nonatomic) NSString* stuNo;
@property (strong, nonatomic) Grade* grade;
- (NSComparisonResult)compare:(Student *)stu;

- (NSString *)description;

@end

@implementation Student
- (NSComparisonResult)compare:(Student *)stu
{
    return [_name compare: [stu name]];
}
- (NSString *)description
{
    return [NSString stringWithFormat:@"%@", _name];
}
@end

 2.2 排序 （使用自定义方法）

//对自定义对象进行排序
        Grade* grade1 = [[Grade alloc] init];
        grade1.name = @"1023";
        Grade* grade2 = [[Grade alloc] init];
        grade2.name = @"1024";
        
        Student* stu1 = [[Student alloc] init];
        stu1.name = @"悟空";
        stu1.stuNo = @"008";
        stu1.age = 10;
        stu1.grade = grade1;
        Student* stu2 = [[Student alloc] init];
        stu2.name = @"八戒";
        stu2.stuNo = @"007";
        stu2.age = 12;
        stu2.grade = grade2;
        Student* stu3 = [[Student alloc] init];
        stu3.name = @"唐僧";
        stu3.stuNo = @"009";
        stu3.age = 14;
        stu3.grade = grade2;
        Student* stu4 = [[Student alloc] init];
        stu4.name = @"玉帝";
        stu4.stuNo = @"011";
        stu4.age = 16;
        stu4.grade = grade1;
        Student* stu5 = [[Student alloc] init];
        stu5.name = @"观音";
        stu5.stuNo = @"112";
        stu5.age = 14;
        stu5.grade = grade1;
        
        NSArray* students = @[stu1, stu2, stu3, stu4,stu5];
        //对自定义对象排序需要自定义排序方法
        NSArray* orderedArr = [students sortedArrayUsingSelector:@selector(compare:)];
//        NSLog(@"%@", orderedArr);
        for (Student *new in orderedArr) {
            NSLog(@"%@", new.name);
        }

 3.使用NSSortDescriptor进行排序，NSSortDescriptor排序更多的用于多条件排序

　　使用步骤：

　　1>创建NSSortDescriptor对象

　　　　　//使用NSSortDescriptor对象描述某一条属性的比较规则
        //第一个参数，是要比较的属性所对应的成员变量的名字
        //第二个参数，指定为YES, 表示为升序，指定为NO,表示为降序
        
        NSSortDescriptor* desc1 = [[NSSortDescriptor alloc] initWithKey:@"_stuNo" ascending:YES];
        NSSortDescriptor* desc2 = [[NSSortDescriptor alloc] initWithKey:@"_age" ascending:YES];
        NSSortDescriptor* desc3 = [[NSSortDescriptor alloc] initWithKey:@"_name" ascending:YES];
        //【注】NSSortDescriptor 支持路径，_grade为student对象的属性对象，name为_grade的属性
        NSSortDescriptor* desc4 = [[NSSortDescriptor alloc] initWithKey:@"_grade.name" ascending:YES];

　　2>将NSSortDescriptor对象放入数组

NSArray* descArr = [NSArray arrayWithObjects: desc4,desc1, desc3, desc2, nil];

　　3>需要排序的数组调用  sortedArrayUsingDescriptors：方法进行排序

NSArray* sortedByDescriptor = [students sortedArrayUsingDescriptors: descArr];

　　实例代码如下：

　　Student.h文件

#import <Foundation/Foundation.h>
@class Grade;
@interface Student : NSObject
@property (copy, nonatomic) NSString* name;
@property (assign, nonatomic) NSInteger age;
@property (copy, nonatomic) NSString* stuNo;
@property (strong, nonatomic) Grade* grade;
- (NSComparisonResult)compare:(Student *)stu;

- (NSString *)description;

@end

　　Student.m文件

#import "Student.h"

@implementation Student
- (NSComparisonResult)compare:(Student *)stu
{
    return [_name compare: [stu name]];
}
- (NSString *)description
{
    return [NSString stringWithFormat:@"%@", _name];
}
@end

　　Grade.h文件

#import <Foundation/Foundation.h>

@interface Grade : NSObject
@property (copy, nonatomic) NSString* name;
@end

　　Grade.m文件

　　

#import "Grade.h"

@implementation Grade

@end

　　主函数：

//对自定义对象进行排序
        Grade* grade1 = [[Grade alloc] init];
        grade1.name = @"1023";
        Grade* grade2 = [[Grade alloc] init];
        grade2.name = @"1024";
        
        Student* stu1 = [[Student alloc] init];
        stu1.name = @"悟空";
        stu1.stuNo = @"008";
        stu1.age = 10;
        stu1.grade = grade1;
        Student* stu2 = [[Student alloc] init];
        stu2.name = @"八戒";
        stu2.stuNo = @"007";
        stu2.age = 12;
        stu2.grade = grade2;
        Student* stu3 = [[Student alloc] init];
        stu3.name = @"唐僧";
        stu3.stuNo = @"009";
        stu3.age = 14;
        stu3.grade = grade2;
        Student* stu4 = [[Student alloc] init];
        stu4.name = @"玉帝";
        stu4.stuNo = @"011";
        stu4.age = 16;
        stu4.grade = grade1;
        Student* stu5 = [[Student alloc] init];
        stu5.name = @"观音";
        stu5.stuNo = @"112";
        stu5.age = 14;
        stu5.grade = grade1;
        
        NSArray* students = @[stu1, stu2, stu3, stu4,stu5];

NSSortDescriptor* desc1 = [[NSSortDescriptor alloc] initWithKey:@"_stuNo" ascending:YES];
        NSSortDescriptor* desc2 = [[NSSortDescriptor alloc] initWithKey:@"_age" ascending:YES];
        NSSortDescriptor* desc3 = [[NSSortDescriptor alloc] initWithKey:@"_name" ascending:YES];
        //可向下传递
        NSSortDescriptor* desc4 = [[NSSortDescriptor alloc] initWithKey:@"_grade.name" ascending:YES];
        NSArray* descArr = [NSArray arrayWithObjects: desc4,desc1, desc3, desc2, nil];
//        NSArray* descArr = [NSArray arrayWithObjects:desc4, nil];
        NSArray* sortedByDescriptor = [students sortedArrayUsingDescriptors: descArr];
        
        for (Student *new in sortedByDescriptor) {
            NSLog(@"%@", new.grade.name);
        }