应用内购买问题

我正在沙盒模式下测试我的应用内购买，但我不明白为什么即使我点击了购买，应用内购买提示框也会不断弹出...

在我点击“购买”后第二次弹出，我点击“取消”并出现错误：

Thread 1:EXC_BAD_ACCESS (code1, address=0x6000008)

我的.m：

• （void）updateCredit {//添加到plist NSArray * paths = NSSearchPathForDirectoriesInDomains（NSDocumentDirectory，NSUserDomainMask，YES）; NSString * documentsDirectory = [paths objectAtIndex：0]; NSString * path = [documentsDirectory stringByAppendingPathComponent：@“data.plist”]; NSMutableArray * currPlist = [[NSMutableArray alloc] initWithContentsOfFile：path];

NSString * lastEx = [currPlist objectAtIndex：0];
int lastScore = [[currPlist objectAtIndex：1] intValue];
int numberOfTries = [[currPlist objectAtIndex：2] intValue];
int totalScore = [[currPlist objectAtIndex：3] intValue];
int avg = [[currPlist objectAtIndex：4] intValue];
int credit = [[currPlist objectAtIndex：5] intValue];

credit = 10;

NSMutableArray * updatePlist = [[NSMutableArray alloc] init];
[updatePlist addObject：lastEx];
[updatePlist addObject：[NSNumber numberWithInt：lastScore]];
[updatePlist addObject：[NSNumber numberWithInt：numberOfTries]];
[updatePlist addObject：[NSNumber numberWithInt：totalScore]];
[updatePlist addObject：[NSNumber numberWithInt：avg]];
[updatePlist addObject：[NSNumber numberWithInt：credit]];
[updatePlist writeToFile：path atomically：YES];
}

-(void)paymentQueue:(SKPaymentQueue *)queue updatedTransactions:(NSArray *)transactions{
    for (SKPaymentTransaction *transaction in transactions) {
        switch (transaction.transactionState) {
            case SKPaymentTransactionStatePurchasing:

            break;
        case SKPaymentTransactionStatePurchased:
            [[SKPaymentQueue defaultQueue]finishTransaction:transaction];
            [self updateCredit];
            [self dismissModalViewControllerAnimated:YES];
            break;

        case SKPaymentTransactionStateRestored:
            [[SKPaymentQueue defaultQueue]finishTransaction:transaction];
            break;

        case SKPaymentTransactionStateFailed:
            if (transaction.error.code != SKErrorPaymentCancelled) {
                UIAlertView *alert2 = [[UIAlertView alloc]initWithTitle:@"Error" message:@"Error updating credit" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
                [alert2 show];
            }
            [[SKPaymentQueue defaultQueue]finishTransaction:transaction];
            break;

        default:
            break;
    }
}
}