實現類時出現Objective-C錯誤？

Question

我有這堂課

#import <Foundation/Foundation.h>

@interface SubscriptionArray : NSObject{
    NSString *title;
    NSString *source;
    NSString *htmlUrl;
}

@property (nonatomic,retain) NSString *title;
@property (nonatomic,retain) NSString *source;
@property (nonatomic,retain) NSString *htmlUrl;

@end

實現文件是這個：

#import "SubscriptionArray.h"

@implementation SubscriptionArray
@synthesize title,source,htmlUrl;

-(void)dealloc{
    [title release];
    [source release];
    [htmlUrl release];
}

@end

當我在本示例中使用此類時，出現EXEC_BAD_ACCESS錯誤：

  for (NSDictionary *element in subs){
            SubscriptionArray *add;
            add.title=[element objectForKey:@"title"];   //ERROR Happens at this line
            add.source=[element objectForKey:@"htmlUrl"];
            add.htmlUrl=[element objectForKey:@"id"];
            [subscriptions addObject:add];


        }

有人能幫我嗎？ PS訂閱是一個NSMutableArray

Answer 1

您需要像這樣分配您的SubscriptionArray對象： SubscriptionArray *add = [[SubscriptionArray alloc] init];

因此，您的for循環將如下所示：

for (NSDictionary *element in subs){
        SubscriptionArray *add = [[SubscriptionArray alloc] init];
        add.title=[element objectForKey:@"title"];
        add.source=[element objectForKey:@"htmlUrl"];
        add.htmlUrl=[element objectForKey:@"id"];
        [subscriptions addObject:add];
        [add release];
}

Answer 2

您需要初始化SubscriptionArray。 即

SubscriptionArray *add = [SubscriptionArray new];