Optimize tableView scrolling - iphone

Question

My tableView scrolls with lags if extra populated. Up to 20 cells go well, but above - it starts lagging while scrolling. Please, suggest an implementation with a better scrolling result. Here is the way I did it:
I have defined a custom UITableViewCell class.
The cell has 4 labels and an imageView (each outlet is a synthesized property):
I have placed a tableView in my viewController, and populated it like this:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *CellIdentifier = #"CustomCell";
MyCustomCell *cell = (MyCustomCell *) [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:#"MyCustomCell" owner:self options:nil];
for (id currentObject in topLevelObjects)
if ([currentObject isKindOfClass:[UITableViewCell class]]){
cell = (MyCustomCell *) currentObject;
break;
}
}
[cell.label_descr setText:#"bla-bla-bla"];
[cell.label_date setText:#"bla-bla-bla"];
[cell.label_time setText:#"bla-bla-bla"];
[cell.label_numeric setText:#"bla-bla-bla"];
[cell.image_view setImage:[UIImage imageWithContentsOfFile:#"bla-bla-bla"]];
return cell;
}
The amount of text in each cell, as you can see, is miserable, and the image used for the UIImageView is about 25x25 .png file.
My tableView is supposed to hold more than 300 cells (don't blame on me, I have a "customer from hell").
Please, suggest a way to make the tableView scroll smoother, without (much) lags. Or an alternative way to present those "damn-over-300-cells" to my "from hell" customer.
300 thanks in advance!
P.S.: sorry if duplicated, but the solutions found didn't help at all.
EDIT:
About the image used for the imageView:
I use 2 different images only:
a "checkmark" - transaction done
and a "pending" - transaction in process
Maybe I use to define 2 imageView outlets in my tableViewCell xib, and just selecting the needed imageView, instead of setting each time the required image?
SOLUTION FOUND, thanks to everybody, especially to iNoob and max_.
In tableViewCell's xib, I have set the "checkMark" as the default image of the imageView.
When defining the cell's values, in cellForRowAtIndexPath, only if needed, I say:
if_I_should_present_a_pending_image:
[cell setPending];
to replace the "checkMark" with a "pending" image (method defined in tableViewCell class):
- (void)setPending{
self.image_view.animationImages = [NSArray arrayWithObjects:
[UIImage imageNamed:#"pending_1.png"],
[UIImage imageNamed:#"pending_2.png"],
[UIImage imageNamed:#"pending_3.png"],
[UIImage imageNamed:#"pending_4.png"],
nil];
self.image_view.animationDuration = 2.0;
self.image_view.animationRepeatCount = 0;
[self.image_view startAnimating];
}
l
After that, the table scrolls like a charm. Thanks to everybody again. Cheers.

Answer 1

Don't iterate through all of the subviews: cell = [topLevelObjects objectAtIndex:0];
Load the images in the background using gcd, and store them in an NSDictionary for easy access:
Pseudo code:
If caches dict contains an object for the URL you want to load
Retrieve that image from the dict
Set it as the image
Else
Load the image using dispatch_async()
Add it to the dict

Answer 2

I found this article suggesting that creating the cells programatically instead of using a nib file could be up to 5-10% faster. I don't know if it's true or not, so take it with a grain of salt, but it may be worth a try.

Answer 3

Replace your code with following one and try it out.
For the below code :
1) Take IBOutlet of your UITableViewCell in the your controller. for below code it is myCustomTableViewCell.
MyCustomCell *customCell = (MyCustomCell *)[tableView dequeueReusableCellWithIdentifier:#"MyCustomCell"];
if(customCell == nil) {
[[NSBundle mainBundle] loadNibNamed:#"MyCustomCell" owner:self options:nil];
customCell = myCustomTableViewCell;
}
Hope it will work.