Error in TableView when reached to the bottom of the Table - ios

Question

I am recieving this error when i scroll to the bottom of my TableView, I dont think its any error with actually retrieving the pictures from the server.:
*** Terminating app due to uncaught exception 'NSRangeException', reason: '-[__NSCFArray objectAtIndex:]: index (15) beyond bounds (15)'
Here is my .m file I cut it to only the actually needed parts of the file:
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [[self entries] count] + tweets.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath.row % 2 == 0) {
NSDictionary *tweet = [tweets objectAtIndex:indexPath.row];
NSString *created = [tweet objectForKey:#"created_at"];
NSLog(#"%#", created);
static NSString *CellIdentifier = #"TweetCell";
UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
NSString *text = [tweet objectForKey:#"text"];
NSString *name = [[tweet objectForKey:#"user"] objectForKey:#"name"];
cell.textLabel.text = text;
cell.detailTextLabel.text = [NSString stringWithFormat:#"by %#", name];
return cell;
}else {
static NSString *CellIdentifier = #"InstagramCell";
UITableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:CellIdentifier];
NSDictionary *entry = [self entries][indexPath.row];
NSString *imageUrlString = entry[#"images"][#"low_resolution"][#"url"];
NSURL *url = [NSURL URLWithString:imageUrlString];
[cell.imageView setImageWithURL:url];
return cell;
}
}
- (void)fetchTweets {
self.twitterClient = [[AFOAuth1Client alloc] initWithBaseURL:[NSURL URLWithString:#"https://api.twitter.com/1.1/"] key:#"TWEETER_KEY" secret:#"TWEETER_SECRET"];
[self.twitterClient authorizeUsingOAuthWithRequestTokenPath:#"/oauth/request_token" userAuthorizationPath:#"/oauth/authorize" callbackURL:[NSURL URLWithString:#"floadt://success"] accessTokenPath:#"/oauth/access_token" accessMethod:#"POST" scope:nil success:^(AFOAuth1Token *accessToken, id responseObject) {
[self.twitterClient registerHTTPOperationClass:[AFJSONRequestOperation class]];
[self.twitterClient getPath:#"statuses/home_timeline.json" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
NSArray *responseArray = (NSArray *)responseObject;
[responseArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
NSLog(#"Success: %#", obj);
tweets = responseArray;
[self.tableView reloadData];
}];
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"Error: %#", error);
}];
} failure:^(NSError *error) {
NSLog(#"Error: %#", error);
}];
}

Answer 1

There needs to be tight coordination between the return value from numberOfRowsInSection and the array access that the code does in cellForRowAtIndexPath.
Consider this, your entries array and tweets array each have 4 elements. So numberOfRowsInSection returns 8. The cellForRowAtIndexPath method gets called to configure row 6. Your code will do this: NSDictionary *tweet = [tweets objectAtIndex:indexPath.row];
But wait... that array has only 4 elements, right? Asking for something at index 6 will generate the crash you see.
It might be simpler to write a methods to interleave the arrays into a single array, then answer the count of the combined array in numberOfRowsInSection. In cellForRowAtIndexPath, the array elements themselves should be able to tell you what kind of row you have (not the index). Dereference the combined array and configure the table accordingly.
EDIT - I'll try to make my advice more explicit in code: Let's say, for simplicity, that "entries" and "tweets" are both arrays of NSDictionaries and that your app wants to organize them in the UI entries first, then tweets.
// in interface:
#property (nonatomic, strong) NSArray *myModel;
// in code:
- (NSArray *)myModel {
if (!_myModel) {
NSMutableArray *array = [NSMutableArray arrayWithArray:[self entries]];
[array addObjectsFromArray:tweets];
_myModel = [NSArray arrayWithArray:array];
}
return _myModel;
}
We call this 'myModel' for a reason. It's the datasource of the table. The datasource protocol is asking explicitly about this array (and no other).
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return self.myModel.count;
}
Now cellForRowAtIndexPath is going to ask you to configure that many (myModel count) rows, numbered 0..count-1. You must dereference the same array -- myModel -- for all datasource methods:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
NSDictionary *myModelForThisRow = self.myModel[indexPath.row];
// get the cell = deque...
cell.textLabel.text = myModelForThisRow[#"someKey"];
return cell;
}
What if your tweets or entries array changes? No problem, just rebuild the model like this:
- (IBAction)tweetsOrEntriesDidChange:(id)sender {
self.myModel = nil; // the "lazy" getter will rebuild it
[self.tableView reloadData]; // this will call the datasource which will call the lazy getter
}

Answer 2

You are trying to go read into an array outside of it's bounds.
That array access look very suspicious
if (indexPath.row % 2 == 0) {
NSDictionary *tweet = [tweets objectAtIndex:indexPath.row];
as well as this one
NSDictionary *entry = [self entries][indexPath.row];
From what I've seen your array tweets and [self entries] don't contain as many object each as there is row in your table section.
I take my assomption from here :
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [[self entries] count] + tweets.count;
}

Answer 3

NSRangeException is thrown because you are trying to access an index which is not within the valid range for your array. Try setting an "Exception breakpoint" in Xcode to see where it's coming from. Check here to know more about Exception breakpoints
This is typically caused by an off by one error.