Table view cells lose their order - ios

Question

Goal
I'm trying to create a table view like Instegram's home screen.
I've made a custom cell, I'm initialising it with data, the cell suppose to hold the "Post".
Logic
I save each cell in a NSMutableDictionary , the key is the index of the posts order and the value is the post it self.
Current Result
I scroll down, and everything is fine. The order you see is post1, post2, post3...post 8 but when I scroll up, everything mess up and the post order is post8, post6, post7, post8, post5... You get the point.
(Before asking here I tried doing it with small objects - a REGULAR ! (not custom) cell containing only strings.
for some reason it worked ! the order was perfect.)
Code
this is my UITableViewController - my "Home" screen "cellForRow" Method.
if we scroll up and the index of the Tableview is alrdy have been initialised, I pull the post form the dictionary.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *PC = #"PostCell";
PostCell *Pcell = [tableView dequeueReusableCellWithIdentifier:PC forIndexPath:indexPath];
NSString *key = [[NSString alloc] initWithFormat:#"%i", indexPath.section];
NSLog(#"Cell %i", indexPath.section);
// Checking if alrdy visted this indexpath.
if (![_allcells objectForKey:key]) {
[self setPostUserName:[[NSString alloc] initWithFormat:#"username: %i", indexPath.section]:Pcell];
// Saving a postcell I wont return, just to save in a dictionary.
// When we get here again it will get another pointer like that my object wont change.
PostCell* toSave = [[PostCell alloc] init];
// saving it with current post data.
[self copyPost:toSave :Pcell];
[_allcells setObject:toSave forKey:key];
}
else {
// Copying post daya
[self copyPost:Pcell :[_allcells objectForKey:key]];
}
NSLog(#"Cell %i Returning: %#", indexPath.section, Pcell.userName.text);
return Pcell;
}
// Check if it reached the end
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
float endScrolling = scrollView.contentOffset.y + scrollView.frame.size.height;
if (endScrolling >= scrollView.contentSize.height)
{
NSDictionary *temparr = [[NSDictionary alloc] initWithDictionary:_allcells];
[self.tableView reloadData];
_allcells = [[NSMutableDictionary alloc] initWithDictionary:temparr];
}
}
and this is my PostCell.h , so you can see the attributes.
#interface PostCell : UITableViewCell
#property (strong, nonatomic) IBOutlet UIImageView *profilePic;
#property (strong, nonatomic) IBOutlet UILabel *userName;
#property (strong, nonatomic) IBOutlet UILabel *checkIn;
#property (strong, nonatomic) IBOutlet UILabel *uploadedAgo;
#property (strong, nonatomic) IBOutlet UIImageView *mainPic;
#property (strong, nonatomic) IBOutlet UILabel *likes;
#property (strong, nonatomic) IBOutlet UILabel *participants;
#end
By the way, if you got a project example that has a result similar to Instagram home screen it would be great if you can link me to it!

Answer 1

You shouldn't store references to the cells, since they are being reused by the tableview when they leave the screen. At the moment everything works fine for you while scrolling down the first time, because you create the cells new. On scrolling up, you get the stored reference which now points to one of the newly created cells, so things look messed up.
What you should do is just populating the reused cells with the right data and only create them if needed. Like:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *PC = #"PostCell";
PostCell *Pcell = (PostCell*)[tableView dequeueReusableCellWithIdentifier:PC forIndexPath:indexPath];
// feed the needed data to the cell
return Pcell;
}
Not sure why you are accessing only indexPath.section since usually you would populate the table with multiple cells per section, using indexPath.row.

Answer 2

Okay, I found out the mistake, Because I was first I was saving the id of each Post and than took it out of the dictionary it didn't work.
than I was trying to only save the attributes of the post by creating a "fake" postCell and saving the attribues of the original cell in the fake cell and than took it out of the array and made the cell copy ONLY the attributes of the cell I just took out and it didn't work.
why? because no matter what I was saving a POINTER ! to those fields !.
I've created a class which was ment to save my desired data that's the class I entered my dictionary.
now each time I dequeue a cell, I load it with the data of the index I'm at. :)
So nice to finally solve it and to learn something new, thanks for giving me leads !

Answer 3

A UITableView works best with an array. Also an array will stay in order as it is indexed, while dictionaries have no index, and thus will not retain order. Also separate cells of the same type, in this case PostCell, should not have different sections, but instead different rows. Use section to separate different categories of cells.
Another tip; NSMutableDictionary takes up more memory than an NSDictionary. Once you have set everything in your NSMutableDictionary, store it in an NSDictionary. If you want to modify it in the future, copy it back into an NSMutableDictionary, modify it, and then store it again as an NSDictionary.
#property (strong, nonatomic) NSDictionary *post;
// To create an NSDictionary
NSMutableDictionary *tempDict = [[NSMutableDictionary alloc] init];
[tempDict setValue:#"74 degrees" forKeyPath:#"weather"];
post = tempDict;
// To modify an NSDictionary
tempDict = [[NSMutableDictionary alloc] initWithDictionary:post];
[tempDict removeObjectForKey:#"weather"];
post = tempDict;
Then store it in an array.
#property (strong, nonatomic) NSArray *allPosts;
// NSMutableArray takes up more memory than NSArray
NSMutableArray *tempArray = [[NSMutableArray alloc] initWithArray:allPosts];
[tempArray addObject:post];
allPosts = tempArray;
Finally, display it in your tableview.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *PC = #"PostCell";
PostCell *pCell = [tableView dequeueReusableCellWithIdentifier:PC];
if (!cell) {
pCcell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:PC];
}
NSDictionary *currentPost = [allPosts objectAtIndex:indexPath.row];
// Instead of having post1, post2, post3 and so forth, each post is now in currentPost. If there are 10 posts, then this function will run 10 times. Just write the code as if you are handling one post, and the UITableView will automatically fill in the rest of the posts for you.
return cell;
}