Question

我需要通过添加符合NSComparisonMethods协议的几种方法来扩展Fraction类。

这是我的代码： Fraction.h

#import <Foundation/Foundation.h>

@protocol NSComparisonMethods

-(BOOL) isEqualTo:(id)object;
-(BOOL) isLessThanOrEqualTo:(id)object;
-(BOOL) isLessThan:(id)object;
-(BOOL) isGreaterThan:(id)object;
-(BOOL) isGreaterThanOrEqualTo:(id)object;
-(BOOL) isNotEqualTo:(id)object;

@end

@interface Fraction : NSObject <NSComparisonMethods>

@property int numerator, denumerator;

-(void) print: (BOOL) test;
-(void) setTo: (int) n over: (int) d;
-(double) convertToNum;
-(void) reduce;
-(id) addFrac:(id)f;
-(void) justPrint;
-(id) initWith:(int)n over:(int)f;
+(Fraction *) allocF;
+(int) count;
+(int) gCounter;

@end

Fraction.m

#import "Fraction.h"

@implementation Fraction

@synthesize numerator, denumerator;

-(BOOL) isEqualTo:(id)object
{
    Fraction *selfCopy = [[Fraction alloc] init];

    if (selfCopy == object) 
        return YES;
    else 
        return NO;
}
//more methods..

的main.m

#import <Foundation/Foundation.h>
#import "Fraction.h"
#import "Fraction+MathOperations.h"

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

    @autoreleasepool {

        Fraction *fracA = [[Fraction alloc] init];
        Fraction *fracB = [[Fraction alloc] init];

        id Object;

        [fracA setTo:1 over:4];
        [fracB setTo:1 over:4];

        Object = fracB;

        NSLog(@"%s",[fracA isEqualTo: Object]? "Yes":"No");
    }

    return 0;
}

是不是假设工作正常？我得No没有得到什么...... 方法实现中的问题是什么？我不能像(selfCopy == object)那样测试对象吗？我应该做selfCopy.numerator（exedra ..）

Answer 1

if (selfCopy == object)

这只检查指针是否相同

试

-(BOOL) isEqualTo:(id)object
{
    return self.numerator == object.numerator && self.denumerator == object.denumerator :
}

好的，这太简单了，因为[fracA setTo:1 over:4]和[fracA setTo:2 over:8]应该相等，但你应该明白这一点。

NSObject为许多这些方法提供的默认实现适用于实现单个比较方法的对象，其选择器，签名和描述符合以下条件：
- (NSComparisonResult)compare:(id)object;
如果接收者小于object，则此方法应返回NSOrderedAscending，如果接收者大于对象，则为NSOrderedDescending 如果接收者和对象相等，则为NSOrderedSame。例如， NSString没有实现在此声明的大多数方法非正式协议，但NSString对象仍然处理消息正确符合此协议，因为NSString实现了比较：满足必要要求的方法。可可也包括适当的比较：NSDate的方法实现， NSDecimalNumber和NSValue类。

所以你应该更好地拥有-compare:之类的

-(NSOrderResult) compare:(Fraction *)otherFraction
{
    Fraction *selfReduced = [self fractionReduced]; // should return a unretaind reduced copy
    Fraction *otherReduced= [otherFraction fractionReduced];
    float selfAbs = (float)selfReduced.nominator / (float)selfReduced.denominator;
    float otherAbs = (float)selfReduced.nominator / (float)selfReduced.denominator;
    if (selfAbs > otherAbs) return NSOrderedAscending;
    if (selfAbs > otherAbs) return NSOrderedDescending;
    return NSOrderedSame;
}

Answer 2

if (selfCopy == object)将始终为false，因为您正在比较指针。

您必须对您的实例进行适当的比较。

我不能像这样测试对象（selfCopy == object）？我应该做selfCopy.numerator

没有。您不需要self的副本。此外，您甚至没有创建self的副本，您只需要分配一个新对象。这就是它的样子。

-(BOOL)isEqualTo:(id)object
{
    if (self.someValue == object.someValue &&
        self.otherValue == object.otherValue) 
        return YES;
    else 
        return NO;
}

Answer 3

我的版本：

-(BOOL) isEqualTo: (Fraction *) f
{
Fraction *temp1 = [[Fraction alloc] init];
Fraction *temp2 = [[Fraction alloc] init];
[temp1 setTo:[self numerator] over:[self denominator]];
[temp2 setTo:[f numerator] over:[f denominator]];
[temp1 reduce];
[temp2 reduce];

return ([temp1 numerator] == [temp2 numerator])
        && ([temp1 denominator] == [temp2 denominator]);
}

将方法添加到符合NSComparisonMethods协议的类时出错

3 个答案: