Adding multiple subviews to UIScrollView - ios

Question

I've been messing around and trying to make my own messaging application (for practice).
I'm adding a custom UIView to a standard UIScrollView based on an IBAction.
Each time the user presses a button, I do the following (in order):
Enumerate the subviews in the scrollView and increase the value of an
integer. I use this int to set the y-position of the new custom
view
Create a custom UIView with a frame size that varies only in width. The view has a UILabel on top of it that has the text.
Create a new CGSize that I use to set the contentSize of the
UIScrollView. The new CGSize is the width of the scrollView + the
height of the custom view + some padding.
I then set the contentSize of the scrollView.
I then add the custom view as a subview of the scrollView.
I created a timer that adds a new message/subview every two seconds to test multiple messages and the issue I am seeing is that once the subviews are added outside the viewable area of the UIScrollView, they stop being added. They are only added once I bring the messages back into the viewable area, and even so, they are added overlaying at times.
Now, I am aware of a few things: I need to add the subviews on a separate thread since they won't be added while the user is scrolling. I know that I will need to "clean up" subviews as they build up since my app will keep eating memory as more subviews are added. I am also aware that I should reposition the UIScrollView as messages are added since it doesn't make sense to add them outside of the viewable area. Finally, I don't think enumerating the subviews is very elegant... so I will change that later... nor is the temp UILabel I make... Now for some code:
- (void)pushMyMessage:(NSString *)message
{
UILabel *tempLabel = [[UILabel alloc]init];
tempLabel.text = message;
[tempLabel sizeToFit];
//adding the new message as a subview below any previous messages
if (self.messageView.subviews.count > 0)
{
int yIndex = 0;
for (SDMessageView *view in self.messageView.subviews)
{
//increase the y value for the frame of the next message
yIndex += view.frame.size.height;
//add a little padding
yIndex += 5;
}
SDMessageView *newMessage = [[SDMessageView alloc]initWithFrame:CGRectMake(20, yIndex, tempLabel.frame.size.width + 8, tempLabel.frame.size.height) setMessage:message];
CGSize newSize = CGSizeMake(self.messageView.frame.size.width, self.messageView.contentSize.height + newMessage.frame.size.height + 30);
[self.messageView setContentSize:newSize];
[self.messageView addSubview:newMessage];
}
else
{
//initial message
SDMessageView *newMessage = [[SDMessageView alloc]initWithFrame:CGRectMake(20, 20, tempLabel.frame.size.width + 8, tempLabel.frame.size.height) setMessage:message];
CGSize newSize = CGSizeMake(self.messageView.frame.size.width, self.messageView.contentSize.height + newMessage.frame.size.height + 30);
[self.messageView setContentSize:newSize];
[self.messageView addSubview:newMessage];
}
}
Any ideas on why the subviews are only added while in view? Also, any ideas on how I can do this efficiently?
Thanks for any help in advance!

Answer 1

Few things I noticed while reading your post:
You should not make any UI interface changes (like adding subviews) on secondary thread, this should be done on main thread.
Why don't you use UITableView for displaying messages? If you use table view, you don't have to calculate all the frames, content sizes and etc., just need to give correct height to the cell, and this would efficient way of solving what you are trying to achieve.
I didn't really understand, why your subviews are not added to the hidden area of the scroll view, in my practice, I didn't notice such a behaviour of the scroll view (I used it a lot), there should be some other issue with your code (are you adding subviews on secondary thread?).
Hope this was helpful, Good Luck!