ScrollView大量使用大量内存的图像

Question

My app for the iPhone Contains 170 images. I read them into an array, and in the loop add a picture in the viewfinder, then put the image View as sub view of scroll view.

When running my app uses too much memory 700mb. I tried to reduce the size of the pictures, but it didn't work.

One of my friends said that I should add only images # 1 and # 2. When the user block is scrolled to the picture No. 1, then only show the picture No. 2. Then the picture No. 1 to remove from the image viewer and add the picture No. 3.

He says that in this way I can maintain the normal memory consumption. But I don't understand how to do this? : D

Could you help with an example? Thanks in advance.

Not using UICollectionView

Here is my code:

- (void) addImageViewToScrollView {

    //create ArrayImages
    NSMutableArray *tempArray = [[NSMutableArray alloc] init];

    for (int x = 0; x < 170; x++) {

        [tempArray addObject:[UIImage imageNamed:[NSString stringWithFormat:@"%d.jpg",x]]];

    }
    self.imagesArray = [NSArray arrayWithArray:tempArray];

    //Frame ScrollView in UIView
    self.scrollView.contentSize =
    CGSizeMake(self.scrollView.frame.size.width * self.imagesArray.count,
           self.scrollView.frame.size.height);

    //scrollView add subview ImageView
    for (int i = 0; i < self.imagesArray.count; i++) {
        CGRect frame;
        frame.origin.x = self.scrollView.frame.size.width * i;
        frame.origin.y = 0;
        frame.size = self.scrollView.frame.size;
        _imageView = [[UIImageView alloc] init];
        _imageView.image = [self.imagesArray objectAtIndex:i];
        _imageView.frame = frame;
        [scrollView addSubview:_imageView];

    }
    self.pageControll.currentPage = 0;
    self.pageControll.numberOfPages = self.imagesArray.count;
}

I decided to split the code for readability

 - (void)scrollViewDidScroll:(UIScrollView *)sender {

    CGFloat pageWidth = self.scrollView.frame.size.width;
    int page = floor((self.scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;

    self.pageControll.currentPage = page;
    self.imageIndex = page;

}

#pragma mark - ChangePage
- (IBAction)changePage {

    CGRect frame;
    frame.origin.x = self.scrollView.frame.size.width * self.pageControll.currentPage;
    frame.origin.y = 0;
    frame.size = self.scrollView.frame.size;
    [self.scrollView scrollRectToVisible:frame animated:YES];
    pageControlBeingUsed = YES;

} 

Answer 1

You can use imageWithContentsOfFile instead of using imageNamed as imageWithContentsOfFile doesn't cache the images. Hence preferable to use, to reduce memory issues.