iphone - 发送到实例的选择器无效 - objectForKey :

Question

我在运行代码时遇到错误。罪魁祸首是我从下面的 plist 访问字符串:

    NSString *sImageFile = [dictionary objectForKey:@"answerCorrect"];
    NSLog(@"%@",sImageFile);

我的 cocos2d Init 中有这个:

-(id) init
{
    // always call "super" init
    // Apple recommends to re-assign "self" with the "super" return value
    if( (self=[super init])) {

        NSUserDefaults *sud = [NSUserDefaults standardUserDefaults];
        NSString *ctlLang = [sud valueForKey:@"ctlLang"];
        NSNumber *questionState = [sud valueForKey:@"questionState"];
        NSNumber *scoreState = [sud valueForKey:@"scoreState"];
        gameArray = (NSMutableArray *)[sud valueForKey:@"gameArray"];
        for (NSString *element in gameArray) {
            NSLog(@"\nQL gameArray value=%d\n", [element intValue]);
        }
        NSString *path = [[NSBundle mainBundle] bundlePath];
        NSString *finalPath = [path stringByAppendingPathComponent:ctlLang];
        dictionary = [NSDictionary dictionaryWithContentsOfFile:finalPath];

        NSString *sImageFile = [dictionary objectForKey:@"answerCorrect"];
        NSLog(@"%@",sImageFile);
    }
}

字符串的打印在场景的初始部分工作正常。问题出现在我后面定义的一个方法中。由于某种原因，它没有在此处显示的方法中返回字符串:

-(void) checkAnswer: (id) sender {

    CGSize size = [[CCDirector sharedDirector] winSize];
    CCMenuItemSprite *sAnswer = (CCMenuItemSprite *)sender;
    NSLog(@"Checking Answer Tag is ---> %d",sAnswer.tag);
    NSString *sImageFile = [dictionary objectForKey:@"answerCorrect"];
    NSLog(@"%@",sImageFile);
    if ([question.answer integerValue] == sAnswer.tag) {
        //...
    }
}

我在这里错过了什么？程序在 NSLog 语句中爆炸。

Answer 1

您将 dictionaryWithContentsOfFile: 返回的对象分配给 dictionary ivar，但您没有通过向它发送 retain 消息来声明对它的所有权对它:

dictionary = [NSDictionary dictionaryWithContentsOfFile:finalPath];

dictionaryWithContentsOfFile: 方法返回一个对象您不拥有。可能在执行 checkAnswer: 时，对象已经被释放。你需要保留它:

dictionary = [[NSDictionary dictionaryWithContentsOfFile:finalPath] retain];

或者使用 alloc-initWithContentsOfFile: 代替，它返回一个你拥有的对象:

dictionary = [[NSDictionary alloc] initWithContentsOfFile:finalPath];

gameplay ivar 也是如此。您不拥有 valueForKey: 返回的对象，您需要保留它。所以这一行:

gameArray = (NSMutableArray *)[sud valueForKey:@"gameArray"];

应该是:

gameArray = [[sud valueForKey:@"gameArray"] retain];