將for循環轉換爲接受ID類型

Question

我希望能夠重用此方法，以便它不受在for循環聲明中調用的類的限制。

問題是編譯器不知道id實際是什麼，所以我不能使用。它的符號。我需要將其轉換爲任何類型的事件類的，我會通過它，而不必重複方法SpecialEvent1SpecialEvent2SpecialEvent3

所以不是for (SpecialEvent1 *event in day)我希望能夠像做for (id event in day)但問題發生時，我嘗試訪問時間或持續時間屬性

- (NSArray *)sumDay:(NSArray *)day { 
    NSInteger morning = 0, afternoon = 0, evening = 0, night = 0; 

    for (SpecialEvent1 *event in day) { 
     NSDate *date = [NSDate dateWithTimeIntervalSinceReferenceDate:event.time]; 
     NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitHour fromDate:date]; 
     NSInteger hour = [components hour]; 

     if (hour < 12) { 
      morning += event.duration; 
     } 
     else if (hour < 18) { 
      afternoon += event.duration; 
     } 
     else if (hour < 20) { 
      evening += event.duration; 
     } 
     else { 
      night += event.duration; 
     } 
    } 

    NSArray *sums = @[@(morning), @(afternoon), @(evening), @(night)]; 
    return sums; 
} 

Answer 1

假設你不感興趣的對象不具有time或duration屬性，你可以定義一個協議，這樣說：

@protocol TimedEvent <NSObject> 
-(NSTimeInterval)time; 
-(NSTimeInterval)duration; 
@end 

然後通過這樣的數組：

- (NSArray *)sumDay:(NSArray *)day { 
    NSInteger morning = 0, afternoon = 0, evening = 0, night = 0; 

    for (id<TimedEvent> event in day) { 
     if (![event conformsToProtocol:@protocol(TimedEvent)]) { 
      continue; 
     } 
     NSDate *date = [NSDate dateWithTimeIntervalSinceReferenceDate:event.time]; 
     NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitHour fromDate:date]; 
     NSInteger hour = [components hour]; 

     if (hour < 12) { 
      morning += event.duration; 
     } 
     else if (hour < 18) { 
      afternoon += event.duration; 
     } 
     else if (hour < 20) { 
      evening += event.duration; 
     } 
     else { 
      night += event.duration; 
     } 
    } 

    NSArray *sums = @[@(morning), @(afternoon), @(evening), @(night)]; 
    return sums; 
}