UITableView with huge number of image - ios

Question

My app needs to display huge number of images(about 2000) in a UITableView. Basically, I use the following code to construct my UITableViewCell:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"Cell"];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:#"Cell"];
}
// Some Operations...
NSString *path = [self.dataArray jk_objectWithIndex:indexPath.row];
UIImage *img = [UIImage imageWithContentsOfFile:path];
cell.imageView.image = img;
return cell;
}
This works but when the tableview loads, memory increase fast and it seems that all the images is loaded to the memory.
Is there any good ideas to deal with this? I just want to save the memory.
BTW, anyone knows what the common way is to achieve this need? I think loading all the images to memory is the stupidest way... And the code I initial rows of tableview is the following:
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
if (!_isLoading) {
return self.dataArray.count; // about 2000... That's terrible
} else {
return 0;
}
}
Thanks!

Answer 1

There are two problems with your code.
First, and most important, the images are large but the display of the images in the table is small. That's wrong. You should load the image only at the size you actually need for display.
Second, images are cached by default. You need to prevent the caching of these images as they are loaded.
You can easily do both of those things in your cellForRowAt by using the ImageIO framework.

Answer 2

I figure out a way to this question. Add these lines of code to cellForRowAtIndexPath:
CGRect rectInTableView = [tableView rectForRowAtIndexPath:indexPath];
CGRect rectInSuperview = [tableView convertRect:rectInTableView toView:[tableView superview]];
if ( rectInSuperview.origin.y > SCREEN_HEIGHT || rectInSuperview.origin.y + rectInSuperview.size.height < 0 ) {
cell.imageView.image = self.placeholder;
} else {
NSString *path = [self.dataArray jk_objectWithIndex:indexPath.row];
UIImage *img = [UIImage imageWithContentsOfFile:path];
cell.imageView.image = img;
}
First I check whether the cell is shown on the screen. If yes, the imageView show my data images. If not, it show the placeholder instead. Also, the placeholder is init with [UIImage imageNamed:]. This is the best way because it will be used frequently.