NSCalendar方法與選擇descriptionWithCalendarFormat錯誤

Question

我從我的代碼得到下面的錯誤：

/Users/user/Dropbox/dev/bignerdranch_cocoa/lottery/LotteryEntry.m:43:16: error: receiver type 'NSCalendar' for instance message does not declare a method with selector 'descriptionWithCalendarFormat:' [4] 

代碼：

// 
// LotteryEntry.m 
// lottery 
// 
// Created by user on 11/7/11. 
// Copyright (c) 2011 __MyCompanyName__. All rights reserved. 
// 

#import "LotteryEntry.h" 

@implementation LotteryEntry 

- (void) prepareRandomNumbers 
{ 
    firstNumber = random() % 100 + 1; 
    secondNumber = random() % 100 + 1; 
} 

- (void) setEntryDate:(NSCalendarDate *)date 
{ 
    entryDate = date; 
} 

- (NSCalendarDate *) entryDate 
{ 
    return entryDate; 
} 

- (int)firstNumber 
{ 
    return firstNumber; 
} 

- (int)secondNumber 
{ 
    return secondNumber; 
} 

- (NSString *)description 
{ 
    NSString *result; 
    result = [[NSString alloc] initWithFormat:@"%@ = %d and %d", 
       [entryDate descriptionWithCalendarFormat:@"%b %d %Y"], 
       firstNumber, secondNumber; 
} 
@end 

Answer 1

因爲該方法descriptionWithCalendarFormat是NSDate，不NSCalendar。