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 = @[@"",@"",@"",@""];
         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 = @"";
         Grade* grade2 = [[Grade alloc] init];
         grade2.name = @"";

         Student* stu1 = [[Student alloc] init];
         stu1.name = @"悟空";
         stu1.stuNo = @"";
         stu1.age = ;
         stu1.grade = grade1;
         Student* stu2 = [[Student alloc] init];
         stu2.name = @"八戒";
         stu2.stuNo = @"";
         stu2.age = ;
         stu2.grade = grade2;
         Student* stu3 = [[Student alloc] init];
         stu3.name = @"唐僧";
         stu3.stuNo = @"";
         stu3.age = ;
         stu3.grade = grade2;
         Student* stu4 = [[Student alloc] init];
         stu4.name = @"玉帝";
         stu4.stuNo = @"";
         stu4.age = ;
         stu4.grade = grade1;
         Student* stu5 = [[Student alloc] init];
         stu5.name = @"观音";
         stu5.stuNo = @"";
         stu5.age = ;
         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 = @"";
         Grade* grade2 = [[Grade alloc] init];
         grade2.name = @"";

         Student* stu1 = [[Student alloc] init];
         stu1.name = @"悟空";
         stu1.stuNo = @"";
         stu1.age = ;
         stu1.grade = grade1;
         Student* stu2 = [[Student alloc] init];
         stu2.name = @"八戒";
         stu2.stuNo = @"";
         stu2.age = ;
         stu2.grade = grade2;
         Student* stu3 = [[Student alloc] init];
         stu3.name = @"唐僧";
         stu3.stuNo = @"";
         stu3.age = ;
         stu3.grade = grade2;
         Student* stu4 = [[Student alloc] init];
         stu4.name = @"玉帝";
         stu4.stuNo = @"";
         stu4.age = ;
         stu4.grade = grade1;
         Student* stu5 = [[Student alloc] init];
         stu5.name = @"观音";
         stu5.stuNo = @"";
         stu5.age = ;
         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);
         }