block ,@selector,排序问题

   NSComparisonResult (^myblock)(id,id) = ^(id obj1,id obj2){
        //  将obj1和obj2由泛型转换为Studet类型
       Student *stu1 = (Student *) obj1;
       Student *stu2 = (Student *) obj2;
       if ( [stu1.name compare:stu2.name]== 1) {
           return NSOrderedAscending;
       }else if([stu1.name compare:stu2.name]== -1){
           return NSOrderedDescending;
       }else{
           return NSOrderedSame;
       }
   };

// 调用block

NSArray *array = [stuarray sortedArrayUsingComparator:myblock];
NSLog(@"==========%@",array);

   //  使用数组方法排序：按照年龄降序排列
    NSArray *sortedArray = [stuarray sortedArrayUsingSelector:@selector(compareByAgeDown:)];
    NSLog(@"%@",sortedArray);
    //  使用数组方法排序：按照ID升序排列
    NSArray *sortedArray1 = [stuarray sortedArrayUsingSelector:@selector(compareByIDUp:)];
    NSLog(@"%@",sortedArray1);
    //  使用数组方法排序：按照name降序排序
   NSArray *sortedArray2 = [stuarray sortedArrayUsingSelector:@selector(compareByNameDown:)];
    NSLog(@"%@",sortedArray2);

Student.h

#import <Foundation/Foundation.h>

@interface Student : NSObject
{
    NSString *_name;
    int _ID;
    int _age;
}

//  声明一个便利构造器
+ (instancetype)studentWithName:(NSString *)name ID:(int)ID age:(int)age;
//使用数组方法排序：按照年龄降序排列
- (NSComparisonResult)compareByAgeDown:(Student *)stu1;
//  使用数组方法排序：按照ID升序排列
- (NSComparisonResult)compareByIDUp:(Student *)stu1;
////  使用数组方法排序：按照name降序排序
//- (NSComparisonResult)compareByNameDown:(Student *)stu1;

// name的getter
- (NSString *)name;
- (int)age;
@end

Student.m

@implementation Student
- (instancetype)initWithName:(NSString *)name ID:(int)ID age:(int)age{
    if (self =[super init]) {
        _name = name;
        _age = age;
        _ID = ID;
    }
    return self;
}

+ (instancetype)studentWithName:(NSString *)name ID:(int)ID age:(int)age{
    return [[[Student alloc] initWithName:name ID:ID age:age] autorelease];
}

- (NSString *)description{
    return [[[NSString alloc] initWithFormat:@"%@ %d %d",_name,_ID,_age] autorelease];
}
//- (NSComparisonResult)compareNumber:(id)num{
//    if(self > num){
//        return NSOrderedDescending;
//    }else if(self < num){
//        return NSOrderedAscending;
//    }else{
//        return NSOrderedSame;
//    }
//}

//  使用数组方法排序：按照年龄降序排列
- (NSComparisonResult)compareByAgeDown:(Student *)stu1{
    
    //  需求是完成降序排列，如果前一个元素小于后一个元素，则需要返回降序，让sortedArrayUsingSelecter：交换这俩个元素。
    if (_age  < stu1 ->_age) {
        return NSOrderedDescending;
        
    }else if(_age >stu1->_age){
        return NSOrderedAscending;
    }else{
        return  NSOrderedSame;
    }
}


//  使用数组方法排序：按照ID升序排列
- (NSComparisonResult)compareByIDUp:(Student *)stu1{
    if (_ID < stu1->_ID) {
        return NSOrderedAscending;
        
    }else if(_ID > stu1->_ID){
        return NSOrderedDescending;
    }else{
        return NSOrderedSame;
    }
}

//  使用数组方法排序：按照name降序排序

- (NSComparisonResult)compareByNameDown:(Student *)stu1{
    if ([_name compare:stu1->_name] == -1) {
        return NSOrderedDescending;
    }else if([self.name compare:stu1.name] == 1){
        return NSOrderedAscending;
        
    }else{
        return NSOrderedSame;
    }
}

- (NSString *)name{
    return _name;
}

- (int)age{
    return _age;
}
@end