Issue with UITableView on scroll - objective-c

Question

I'm experiencing an issue with my UITableView which fetches data from a data table on parse.com. The issue is that every time I scroll down, hiding the first cell completely and then scroll back up, the text on the first cell's titleL is that of another cell. Kindly look at my code and let me know what I'm doing wrong. Also are there any better practices for my code when working with UITableViews in the future?
Code
- (void)viewDidLoad {
[super viewDidLoad];
[self someMethod];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
NSString *CellIdentifer = [NSString stringWithFormat:#"CellIdentifier%i",num];
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifer];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifer];
}
UILabel *titleL = [[UILabel alloc] initWithFrame:CGRectMake(10,10,300,20)];
titleL.text = myTitle;
[cell addSubview:titleL];
return cell;
}
-(void) someMethod {
for (int i = 0; i < arr.count; i++) {
PFQuery *query = [PFQuery queryWithClassName:#"SomeClass"];
[query whereKey:#"objectId" equalTo:[arr objectAtIndex:i]];
[query getFirstObjectInBackgroundWithBlock:^(PFObject *object, NSError *error) {
if (!object) {
} else {
myTitle = [object objectForKey:#"title"];
num = i;
[feed beginUpdates];
[feed reloadRowsAtIndexPaths:myArr withRowAnimation:UITableViewRowAnimationAutomatic];
[feed endUpdates];
}
}];
}
}

Answer 1

You need to write your your tableView:cellForRowAtIndexPath: in such a way that it doesn't matter in which order it is called.
That method is called whenever the UITableView needs to get a cell (sometimes this doesn't mean that it's displayed). It will get called multiple times and you cannot rely on a specific order (for obvious reasons: you cannot predict how the user will scroll).
Now, your problem is that your implementation uses myTitle to assign a title. But that value is not calculated inside tableView:cellForRowAtIndexPath:. You need to change your code in such a way that you always can access the required value for your index path, no matter in which order or how often that method is called.
For example, in someMethod you can store your values from [object objectForKey:#"title"] in an NSMutableArray or in a NSMutableDictionary (with #(i) as key). Then you can query the title for each index path in tableView:cellForRowAtIndexPath:.