Obj-C UIImageView不显示来自NSArray的图像

Question

我正在用Obj-c做一点自学，并且有兴趣制作闪存卡应用程序。我有一个NSArray，对象中有5个图像。当用户按下前进按钮时，我试图让我的UIImageView显示数组中的下一个图像。我从我的数组中获取图像的行上获得了线程1：EXC_BAD_ACCESS（Code = 2，address = 0x0）。这是我当前的标题和实现文件。

@interface WhoAmIViewController : UIViewController

@property (strong, nonatomic) IBOutlet UIImageView *flashcardviewer;
@property (strong, nonatomic) NSArray *aryFlashcards;
@property (nonatomic) NSUInteger *int_counter;
@end


@implementation WhoAmIViewController
@synthesize aryFlashcards;
@synthesize flashcardviewer;
@synthesize int_counter;


- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    aryFlashcards = [NSArray arrayWithObjects:
                                        [UIImage imageNamed:@"shot_1"],
                                        [UIImage imageNamed:@"shot_2"],
                                        [UIImage imageNamed:@"shot_3"],
                                        [UIImage imageNamed:@"shot_4"],
                                        [UIImage imageNamed:@"shot_5"],
                                         nil];
    int_counter = 0;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

//back button
- (IBAction)btn_back:(UIButton *)sender {
}

//forward button
- (IBAction)btn_forward:(UIButton *)sender
{


    flashcardviewer = [[UIImageView alloc]init];
    UIImage *flashcard_next = [UIImage imageNamed:[aryFlashcards objectAtIndex:*(int_counter)]]; //This is where Xcode throws me an error. 
    flashcardviewer.image = flashcard_next;
    int_counter++;


}

//random button
- (IBAction)btn_random:(UIButton *)sender
    {

}

Answer 1

请尝试以下代码：

//Declare int_counter like this
@property (nonatomic) NSUInteger int_counter;

//Set btn_forward: this way
- (IBAction)btn_forward:(UIButton *)sender
{
    //Avoid possible app crash with a if condition 
    if (int_counter < flashcard_next.count) {
        UIImage *flashcard_next = [aryFlashcards objectAtIndex:int_counter];
        flashcardviewer.image = flashcard_next;
        int_counter++;
    } else {
        NSLog (@"No more cards");
    }
}

您可以了解更多关于NSInteger here的信息。

Answer 2

你使int_counter成为指针而不是NSInteger。尝试

@property (nonatomic) NSUInteger int_counter;

和

    UIImage *flashcard_next = [aryFlashcards objectAtIndex:int_counter]; 

Answer 3

你的问题就在这条线上：

UIImage *flashcard_next = [UIImage imageNamed:[aryFlashcards objectAtIndex:*(int_counter)]]; 

你正在创建一个UIImage对象，并在它期待一个UIImage时将另一个NSString传递给该方法。将其更改为：

UIImage *flashcard_next = [aryFlashcards objectAtIndex:int_counter]; 

并且如在另一个答案中提到的，删除指向int_counter的指针。

Answer 4

您的iVar aryFlashcards已在viewDidLoad方法中使用5个图像进行实例化。在你的btn_forward方法实现中你应该替换

UIImage *flashcard_next = [UIImage imageNamed:[aryFlashcards objectAtIndex:*(int_counter)]]; 

使用以下提供的*（int_counter）小于aryFlashCards大小，在您的示例中看起来为5，否则您的应用将抛出超出绑定的异常。

UIImage *flashcard_next = [aryFlashcards objectAtIndex:*(int_counter)];