UITableView lagging when scrolling for chat like app - ios

Question

I have a chat function in the app I am making. Each cell has a UITextView and I need to calculate the **height and width** of each cell. I do that and then cache that data.
Using NSLog I have determined that the data is correctly cached and the height for each row is only being asked for once.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
Message *message = [feedItems objectAtIndex:indexPath.row];
NSString *reuseIdentifier;
if (message.iSentThisMessage) {
reuseIdentifier = #"MeCell";
} else {
reuseIdentifier = #"HostCell";
}
ChatTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:reuseIdentifier forIndexPath:indexPath];
// Configure the cell...
cell.textView.text = message.content;
if (message.frame.size.height == 0 && message.frame.size.width == 0) {
CGRect rect = cell.textView.frame;
rect.origin.x = 5;
rect.origin.y = 3;
CGSize size = [self text:message.content
sizeWithFont:[UIFont systemFontOfSize:17.0]
constrainedToSize:CGSizeMake(225.0, CGFLOAT_MAX)];
rect.size.height = size.height
+ cell.textView.textContainerInset.bottom
+ cell.textView.textContainerInset.top;
rect.size.width = [cell.textView sizeThatFits:CGSizeMake(225.0, rect.size.height)].width
+ cell.textView.textContainerInset.left
+ cell.textView.textContainerInset.right;
if (message.iSentThisMessage) {
rect.origin.x = 320 - (rect.origin.y + rect.size.width);
}
cell.textView.frame = rect;
message.frame = rect;
NSLog(#"Not Cached :(");
} else {
cell.textView.frame = message.frame;
NSLog(#"Cached!");
}
return cell;
}
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
Message *message = [feedItems objectAtIndex:indexPath.row];
CGSize size = [self text:message.content
sizeWithFont:[UIFont systemFontOfSize:17.0]
constrainedToSize:CGSizeMake(225.0, CGFLOAT_MAX)];
if (indexPath.row + 1 == feedItems.count)
size.height += 4;
NSLog(#"Height asked for.");
return size.height + 12;
}
Also, one other possibility may be that I am overriding the following method in my custom uitableviewcell class because otherwise it rearranges the contents of my cell.
- (void) layoutSublayersOfLayer:(CALayer *)layer {
}
I can't seem to figure out how to make it not lag!!

Answer 1

Not clear why you're using a text view, but you should change to a label if you can.
Also, don't cache the height in your table delegate method, that's a nasty side effect. Calculate the height up front, either when the message is loaded / received, or on a background thread for batch load.
The text view / label frame should also be relative to the cell, either by auto resizing / layout. So you should never set it explicitly.
On top of that - profile using instruments. This is the only thing that will really tell you what's wrong.