sortUsingSelector使用方法,以及原理

    在IOS軟件開發(fā)中我們需要依據(jù)NSArray中對(duì)象的成員進(jìn)行排序,我們知道對(duì)象中成員比較多,因此如果我們寫了多種方法根據(jù)不同的成員進(jìn)行排序,代碼量很大,實(shí)現(xiàn)起來不是很方便,因此蘋果向我們提供了一種快速排序的方法,叫做

- (void)sortUsingSelector:(SEL)comparator;

本文重視講訴原理:

    我們先來看一個(gè)例子:

#import <Foundation/Foundation.h>

//Dog頭文件
@interface Dog : NSObject
{
    NSString * _name;
    NSUInteger _age;
}
-(NSComparisonResult)nameCompae:(Dog *)dog;
-(NSComparisonResult)ageCompae:(Dog *)dog;
-(id)initWithName:(NSString *)name andWithAge:(NSUInteger)age;
@property (copy,readwrite,nonatomic) NSString * name;
@property (assign,readwrite,nonatomic)NSUInteger age;
@end

//Dog函數(shù)實(shí)現(xiàn)體
@implementation Dog

-(NSComparisonResult)nameCompae:(Dog *)dog
{
    if ([_name compare:[dog name]]>0)
    {
        return NSOrderedDescending;
    }
    
    return NSOrderedAscending;
}

-(NSComparisonResult)ageCompae:(Dog *)dog
{
    
    NSLog(@"%ld %ld",_age,[dog age]);
    
    if (_age > [dog age]) {
        
        return NSOrderedAscending;
    }
    return NSOrderedDescending;
}
-(void)setAge:(NSUInteger)age
{
    _age = age;
    NSLog(@"dasdsd");
}

-(id)initWithName:(NSString *)name andWithAge:(NSUInteger)age
{
    if (self = [super init]) {
        _name = name;
        _age = age;
    }
    return self;
}

@end

//main函數(shù)
int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        NSMutableArray * dogArray = [[NSMutableArray alloc]init];
        
        Dog * dog1 = [[Dog alloc]initWithName:@"xiaobao" andWithAge:12];
        Dog * dog2 = [[Dog alloc]initWithName:@"zhansan" andWithAge:8];
        Dog * dog3 = [[Dog alloc]initWithName:@"lisi" andWithAge:16];
        Dog * dog4 = [[Dog alloc]initWithName:@"wangwu" andWithAge:7];
        
        [dogArray addObject:dog1];
        [dogArray addObject:dog2];
        [dogArray addObject:dog3];
        [dogArray addObject:dog4];
        
        for (Dog * temp in dogArray) {
            NSLog(@"%@ %ld",temp.name,temp.age);
        }
        
        [dogArray sortUsingSelector:@selector(nameCompae:)];
        
        
        for (Dog * temp in dogArray)
        {
            NSLog(@"%@ %ld",temp.name,temp.age);
        }
        
        [dogArray sortUsingSelector:@selector(ageCompae:)];
        
        
        for (Dog * temp in dogArray)
        {
            NSLog(@"%@ %ld",temp.name,temp.age);
        }
    }
    return 0;
}

    在上面的這個(gè)例子中,我將小狗對(duì)象存入dogArray中,而該對(duì)象中又有兩個(gè)成員變量,一個(gè)是狗的名字,另一個(gè)是狗的年齡,我們通過這兩個(gè)屬性對(duì)這個(gè)dogArray中得對(duì)象進(jìn)行排序,在測(cè)試中我發(fā)現(xiàn)在調(diào)用sortUsingSelector函數(shù)時(shí),選擇器(即ageCompae:和nameCompae)是被多次調(diào)用的,因此我猜測(cè),該函數(shù)的偽代碼如下:

- (void)mysortUsingSelector:(SEL)comparator:①

{

    int temp = 0;

    for (int i=0; i<[self count]-1; i++)②

    {   temp = i;

        for (int j=i+1; j<[self count]; j++)

        {

            if ([[self objectAtIndex:temp] comparator:[self objectAtIndex:j]]==NSOrderedDescending)③

            {

                temp = j;

            }

        }

        if (i!=temp)

        {

            [dogArray exchangeObjectAtIndex:i withObjectAtIndex:temp];

        }

    }

}

上述代碼中又三點(diǎn)需要理解,只要理解了這個(gè)偽代碼,你就知道sortUsingSelector這個(gè)函數(shù)是怎么工作的了.

①:(SEL)comparator:這個(gè)東西其實(shí)就是模仿C語言中的函數(shù)指針,我們想要使用什么函數(shù)對(duì)NSArray的對(duì)象只要把函數(shù)入口地址傳給它就好了,例如上述代碼中想使用dog名字進(jìn)行排序,只要把nameCompae:傳給它就好了,而想要按照年齡排序就傳ageCompare:如果你理解函數(shù)指針,這個(gè)對(duì)你就很簡單了,呵呵

②:這個(gè)self其實(shí)就是數(shù)組的地址,對(duì)應(yīng)與上面代碼中的dogArray

③:使用傳遞過來的函數(shù)進(jìn)行比較,也就是C語言中函數(shù)指針的回調(diào)函數(shù),上述代碼中有一點(diǎn)很重要,也就是

if ([[self objectAtIndex:temp] comparator:[self objectAtIndex:j]]==NSOrderedDescending)這有在這個(gè)語句為真的時(shí)候才會(huì)進(jìn)行交換,我測(cè)試多次sortUsingSelector這個(gè)函數(shù)在回調(diào)(SEL)comparator:函數(shù)時(shí),只有在(SEL)comparator:函數(shù)返回值為NSOrderedDescending:才會(huì)進(jìn)行排序,對(duì)于其它值則不會(huì)進(jìn)行如何處理,這也很好的解釋了我上面的if語句的書寫方式是正確的.

    總結(jié):相信到了這里你一定明白了sortUsingSelector的工作方式了,如果不明白建議看看關(guān)于函數(shù)指針的視頻或者書籍,推薦在51CTO上面找找;