Application Termination because of NSRangeException (NSMutableArray) - ios

Question

I'm trying to retrieve uploaded thumbnailPhotos from Parse to display them in UITableViewCells, but I get an exception thrown in everytime. The error code is as follows: "Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 1 beyond bounds [0 .. 0]'"
This is my code:
- (void) viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
PFQuery *query = [PFQuery queryWithClassName:#"Events"];
[query orderByDescending:#"date"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (error) {
NSLog(#"Error: %# %#", error, [error userInfo]);
} else {
self.events = (NSMutableArray *) objects;
[self.tableView reloadData];
for (PFObject *event in self.events) {
NSInteger index = [self.events indexOfObject:event];
PFFile *imageFile = [event objectForKey:#"thumbnailImage"];
[imageFile getDataInBackgroundWithBlock:^(NSData *result, NSError *error) {
if (error) {
//Handle Error
} else {
UIImage *image = [UIImage imageWithData:result];
if (self.thumbnailPhotos == nil) {
self.thumbnailPhotos = [NSMutableArray array];
self.thumbnailPhotos[index] = image;
} else {
self.thumbnailPhotos[index] = image;
}
[self.tableView reloadData];
}
}];
}
}
}];
}
CellForRowAtIndexPath:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *reuseIdentifier = #"Cell";
EventsTableViewCell *cell = (EventsTableViewCell *)[tableView dequeueReusableCellWithIdentifier:reuseIdentifier forIndexPath:indexPath];
PFObject *event = [self.events objectAtIndex:indexPath.row];
NSDate *date = [event objectForKey:#"date"];
NSString *dateString = [self.dateFormat stringFromDate:date];
NSString *timeString = [self.timeFormat stringFromDate:date];
NSLog(#"IndexPath.row = %ld", (long)indexPath.row);
if ([self.thumbnailPhotos objectAtIndex:indexPath.row] != nil) {
cell.imageView.image = self.thumbnailPhotos[indexPath.row];
} else {
NSLog(#"Nil, Application will crash!");
}
cell.eventNameLabel.text = [event objectForKey:#"title"];
cell.dateLabel.text = dateString;
cell.timeLabel.text = timeString;
[cell.timeLabel sizeToFit];
return cell;
}`
I had to add the index value of self.events because the thumbnailPhotos were downloaded in different speed, so my Cells always showed the wrong photo for the wrong event.
I hope this was enough details to figure the problem out.

Answer 1

Application is crashing because thumbnailPhotos doesn't have any object at index for assignment. Please use following code.
Updated Code which will support Dictionary to hold thumbnail images
/*
Define events as NSMutableArray which holds all events
Define thumbnailPhotos as NSMutableDictionary which holds thumbnail image for index as key
*/
//Create a weak Reference of self for accessing self within block
__weak __typeof(self)weakSelf = self;
PFQuery *query = [PFQuery queryWithClassName:#"Events"];
[query orderByDescending:#"date"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (error) {
NSLog(#"Error: %# %#", error, [error userInfo]);
} else {
//Create a strong reference for updating the UI
__strong __typeof(weakSelf)strongSelf = weakSelf;
//Assign the events to instance object
strongSelf.events = [NSMutableArray arrayWithArray:objects];
//Alloced thumbnail dictionary
strongSelf.thumbnailPhotos = [NSMutableDictionary dictionary];
//Reload tableView so that data will be visible
[strongSelf.tableView reloadData];
for (PFObject *event in strongSelf.events) {
//Define index as block type because we have to use this instance within block
__block NSInteger index = [strongSelf.events indexOfObject:event];
PFFile *imageFile = [event objectForKey:#"thumbnailImage"];
[imageFile getDataInBackgroundWithBlock:^(NSData *result, NSError *error) {
if (error) {
//Handle Error
} else {
UIImage *image = [UIImage imageWithData:result];
//Set the image against index
[strongSelf.thumbnailPhotos setObject:#"" forKey:#(index)];
//Reload only cell for which image is just downloaded
[strongSelf.tableView reloadRowsAtIndexPaths:#[[NSIndexPath indexPathForRow:index inSection:0]] withRowAnimation:UITableViewRowAnimationAutomatic];
}
}];
}
}
}];
Updated:
Modify your cellForRowAtIndexPath as below
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *reuseIdentifier = #"Cell";
EventsTableViewCell *cell = (EventsTableViewCell *)[tableView dequeueReusableCellWithIdentifier:reuseIdentifier forIndexPath:indexPath];
PFObject *event = [self.events objectAtIndex:indexPath.row];
NSDate *date = [event objectForKey:#"date"];
NSString *dateString = [self.dateFormat stringFromDate:date];
NSString *timeString = [self.timeFormat stringFromDate:date];
NSLog(#"IndexPath.row = %ld", (long)indexPath.row);
if ([self.thumbnailPhotos valueForKey:#(indexPath.row)]) {
cell.imageView.image = [self.thumbnailPhotos valueForKey:#(indexPath.row)];
} else {
NSLog(#"Nil, Application will crash!");
}
cell.eventNameLabel.text = [event objectForKey:#"title"];
cell.dateLabel.text = dateString;
cell.timeLabel.text = timeString;
[cell.timeLabel sizeToFit];
return cell;
}
In this implementation thumbnail Image is getting saved in to dictionary and second reload of tableView is per cell basis instead of reloading complete tableView for single thumbnail download.