在自動發布的ios項目中保留變量

Question

我是ios編程的初學者，我的項目將其設置為自動釋放，現在我遇到了自動釋放功能的問題。 我顯示我的代碼，希望您可以支持我以避免這種情況

- (void)initPhotoImage
{
    photoImage = [[MyPhotoImageView alloc] initWithFrame:CGRectMake(5, 30, 0, 0)];
    photoImage.photoViewController = self;
    [photoView addSubview:photoImage];

    UISwipeGestureRecognizer *gesture = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(didSwipeLeft:)];
    gesture.direction = UISwipeGestureRecognizerDirectionLeft;
    [photoView addGestureRecognizer:gesture];
    UISwipeGestureRecognizer *gesture1 = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(didSwipeRight:)];
    gesture1.direction = UISwipeGestureRecognizerDirectionRight;
    [photoView addGestureRecognizer:gesture1];

}

-(void)didSwipeLeft:(UIGestureRecognizer *)gestureRecognizer {

    if(self.nextViewController != NULL){
        [UIView animateWithDuration:1 animations:^{
            self.view.frame = CGRectMake(-1*self.view.frame.size.width, 0, self.view.frame.size.width, self.view.frame.size.height);
        }];
        NSLog(@"next");
    }else{
        NSLog(@"next view is null");
    }
}

這兩個函數在同一類中，我在init函數中打印self.nextViewController，它打印一個地址，但是在swip函數中，我再次打印self.nextViewController，但是它打印空地址，在.h文件中，我定義了它保留

@property (retain, nonatomic) MyPhotoViewController *nextViewController;

Answer 1

改變這個

if(self.nextViewController != NULL)

至

if(self.nextViewController != nil)