Question

I wanted to create a gallery. It loads different images based on the category, that a user selects. I used to populate images in UIImageViews.

My when selecting different categories is that it does not clear the previously selected images. This is my code for populating images.

-(void)refresh{

   categoryLabel.text = treatment.treatmentName;
   NSMutableArray  *galleryImages =[NSMutableArray alloc] ;
   galleryImages = [[PatientImage alloc]find:treatment.treatmentId];

   int imgCount = [galleryImages count];

    for(int i=0;i<imgCount;i++){

        PatientImage *apatientImage = [galleryImages objectAtIndex:i]; 

        UIImage *img1 = [UIImage imageNamed:apatientImage.imageBefore]; 
        UIImageView *myImageView = [[UIImageView alloc] initWithImage:img1];
        myImageView.contentMode = UIViewContentModeTopRight;
        myImageView.frame = CGRectMake(120+i*240,120.0,100.0, 100.0);
       [self.view addSubview:myImageView];

        UIImage *img2 = [UIImage imageNamed:apatientImage.imageAfter]; 
        UIImageView *myImageView2 = [[UIImageView alloc] initWithImage:img2];
        myImageView2.contentMode = UIViewContentModeTopRight;
        myImageView2.frame = CGRectMake(120+i*240+300,120.0,100.0, 100.0);
        [self.view addSubview:myImageView2];
    }
}  

Answer 1

First things first, You have some memory leaks there. You are allocating UIImageViews but are not releasing them anywhere, after you have added them to your view. I don’t know if that applies to ARC, though. Same applies to your Mutable array, but I suppose you are releasing it after the ‘for’ loop somewhere, since it seems you posted code after omitting some of it.

As far as your actual question is concerned, I wouldn’t do this this way. I would make the mutable array an object variable, and then fill it with my image views. When calling refresh again, I would first call -removeFromSuperview on each image view, then empty the array, then repopulate it and add the new subviews to my view. That is the simple way.

I don’t know if you are using ARC, but you should be careful about memory management when using dynamically loaded views. Each time you add a view to another one, you increase its retain counter. You must then call release to remove ownership, and let the iOS runtime handle the rest.

Also note that operations such as this using views are expensive in terms of memory. So, another way of repopulating the gallery view is to just change the image an imageView holds. That will save you some memory, and time. In case the view doesn’t have a constant number of images to be displayed, you can refine your algorithm to change the images on the already created image views, and then add more image views if necessary or delete the remaining ones, if any.

I hope I helped.