NSArray API 学习

主要介绍几个非常酷的方法：

1.  排序

-  (NSArray*)sortedArrayUsingSelector:(SEL)aSelector; 

数组排序，返回排好序的新数组。

- (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr

通过块进行数组排序。

- (NSArray *)sortedArrayUsingDescriptors:(NSArray *)sortDescriptors

通过排序描述器，构建复杂排序。

code 1：

NSArray *newArray = [array sortedArrayUsingSelector:@selector(compare:)];

code 2：

Book *book1 = [Book name:@"ABC" type:@"jsj"];  
Book *book2 = [Book name:@"234" type:@"sx"];    
NSArray *array = [NSArray arrayWithObjects:book1,book2, nil];  
NSArray *array2 = [array sortedArrayUsingSelector:@selector(compareBook:)];   

/// Book class 里实现的比较方法
- (NSComparisonResult)compareBook:(Book *)book {  
    NSComparisonResult result = [self.type compare:book.type];  
    // 类型相同，比较名字 
    if (result == NSOrderedSame) {  
        result = [self.name compare:book.name];  
    }  
    return result;  
} 

code 3：

NSArray *new2 = [new sortedArrayUsingComparator:^NSComparisonResult(NSString *str1, NSString *str2){
        return [str1 compare:str2];
    }];

code 4:

    // 1.按姓排序  
    NSSortDescriptor *lastnameDesc = [NSSortDescriptor sortDescriptorWithKey:@"lastname" ascending:YES];  
    // 2.再按名排序  
    NSSortDescriptor *firstnameDesc = [NSSortDescriptor sortDescriptorWithKey:@"firstname" ascending:YES];  
    NSArray *descs = [NSArray arrayWithObjects:lastnameDesc, firstnameDesc, nil nil];  
    NSArray *newArray3 = [array sortedArrayUsingDescriptors:descs]; 

2. 

- (void)makeObjectsPerformSelector:(SEL)aSelector;
- (void)makeObjectsPerformSelector:(SEL)aSelector withObject:(nullable id)argument;

效率高于for循环，类似于NSNotifation机制，并发执行，数组中每个元素执行aSelector中方法。

3. 
- (NSString *)componentsJoinedByString:(NSString *)separator;

将数组转换成字符串；

- (NSArray*)componentsSeparatedByString:(NSString*)separator;

将字符串转换成数组；

code：

 NSArray  *array = [strName componentsSeparatedByString:@","];

 NSString *strings = [nameArray componentsJoinedByString:@","];