objective-c - IOS/Objective-C 我可以将对象存储在本地声明的 NSMutableArray 中。为什么我不能将它们存储在另一个类的对象中的相同类型的数组中？

Question

我发现的最佳相关讨论:Making an array of Objects in Objective-C. .浏览了我准备这篇文章时出现的链接。

自学模式，创建迷你应用程序来强化和扩展我在书籍教程中获得的想法。
………………。

目标:将一些对象(例如类“Trip”)存储在一个可变数组中，包含在另一个对象(例如类“TourCompany”)中。

(两个不同的类接口(interface)文件的一部分)

    @interface Trip : NSObject
    @property (strong, nonatomic) NSString *travelToLocation;

……

        @interface TourCompany : NSObject
        @property (strong, nonatomic) NSMutableArray *trips ;

...... 代码和目标......

1) 证明我创建了 3 个行程对象并且可以访问 travelToLocation ivar
……

        Trip *trip0 = [[Trip alloc] init];
        Trip *trip1 = [[Trip alloc] init];
        Trip *trip2 = [[Trip alloc] init];

        [trip0 setTravelToLocation:@"Vienna"];
        [trip1 setTravelToLocation:@"Mt. St. Helens"];
        [trip2 setTravelToLocation:@"Tenochtitlan"];

        NSString *somePlace1 = trip1.travelToLocation;

        NSLog(@" %@ %@, \n \t Let's LOOK at one particular trip ivar %@.", twoBlanks, nuLn, somePlace1);

     //  CONSOLE RESULTS
      //     Let's LOOK at one particular trip ivar Mt. St. Helens.

……
2) 证明我
i) 可以将这 3 个行程对象存储在本地声明的 NSMutable 数组中
ii) 可以访问 travelToLocation ivar
……

     // put trip objects into a LOCALLY DECLARED mutable array
        NSMutableArray *localTripsArray = [NSMutableArray array ];

      //[myArray addObject: someOtherPerson]; - compare to a STackOverflow discussion

        [localTripsArray addObject:trip0];
     [localTripsArray addObject:trip1];
        [localTripsArray addObject:trip2];


        for (Trip *t in localTripsArray) {

            NSLog(@"\n \t ^^^Trip location in LOCAL TRIPS Mutable ARRAY is %@", t.travelToLocation );

     }



    /*
        CONSOLE RESULTS
     objectInMutableArrayMiniAppChallenge[521:f803] 
        ^^^Trip location in LOCAL TRIPS Mutable ARRAY is Vienna
2012-07-05 13:47:17.172 objectInMutableArrayMiniAppChallenge[521:f803] 
        ^^^Trip location in LOCAL TRIPS Mutable ARRAY is Mt. St. Helens
        2012-07-05 13:47:17.172 objectInMutableArrayMiniAppChallenge[521:f803] 
         ^^^Trip location in LOCAL TRIPS Mutable ARRAY is Tenochtitlan

        */

……
3)但我不知道为什么我不将这 3 个对象存储在我的 TourCompany 类('friendlySkiesTourCo')的实例中的 NSMutable 数组('trips')中
...
//现在在我的 TourCompany 类中实例化一个对象

    TourCompany *friendlySkiesTourCo = [[TourCompany alloc] init];

 // put those same objects into the trips ivar in that object
 //[myArray addObject: someOtherPerson]; 
    //     - compare to a STackOverflow discussion
    //only difference I see is that instead of locally declared 'myArray'
    //   I'm using an ivar that's a member of an object
 // I know there's are values in those objects, because I displayed them above


 [friendlySkiesTourCo.trips addObject:trip0];
    [friendlySkiesTourCo.trips addObject:trip1];
    [friendlySkiesTourCo.trips addObject:trip2];


    for (Trip *t in friendlySkiesTourCo.trips) {

NSLog(@"\n\t+++ TourCompany 类对象 'friendlySkiesTourCo' 对象中的 'trips' 可变数组中的行程位置是 %@", t.travelToLocation );

    }


    /* Console NON-Results

    I never get any output from this NSLog directive
     I'll bet there is something pretty basic I don't understand
     No doubt, it's in the Gol Durned Manual online , but I'm not seeing it
     */

……
4. 让我们仔细检查一下问题是否可能是设置类型问题
……
//我不认为我真的将对象正确地放入了friendlySkies 对象中的这个特定的可变数组中
//让我们检查一下

 int howManyTripsInMutableArray = [friendlySkiesTourCo.trips count];

 NSLog(@"\n \tThere are %d trips for the friendlySkiesTour Co ", howManyTripsInMutableArray);

        /*

     Sure enough...

     2012-07-05 13:53:53.235 objectInMutableArrayMiniAppChallenge[555:f803] 
    There are 0 trips for the friendlySkiesTour Co 

    */

感谢您提供任何线索。我希望我简洁地完成了这篇文章，并且您不会认为我只是没有 RTGDM(如果您想知道，那是'gol durn')，因为我确实尝试过。

月桂树

Answer 1

我敢打赌你没有初始化 friendlySkiesTourCo.trips . IE

friendlySkiesTourCo.trips = [[NSMutableArray alloc] init];

编辑

正如@Chuck 在下面的评论中指出的那样，这种分配实际上应该在类的初始化方法中完成:

@implementation TourCompany

-(id) init
{
    self = [super init];

    self.trips = [[NSMutableArray alloc] init];

    return self;
}