数据源为空时，UITableView调用委托方法

Question

I've got my cellForRowAtIndexPath delegate method defined as so:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    PLOTCheckinTableViewCell *cell = (PLOTCheckinTableViewCell *)[tableView dequeueReusableCellWithIdentifier:CheckinCellIdentifier forIndexPath:indexPath];
    if([self.items count] == 0){
        return cell;
    }
    NSDictionary *checkin = self.items[indexPath.row];
    // configure and return custom cell
}

I'm using a custom cell class ( PLOTCheckinTableViewCell ).

I faced an issue where the user would pull to refresh and then attempt to pull again before the first request had completed (on completion of the request, I reload the table data). When they did this, the app would crash and say that indexPath.row was basically out of bounds, ie. the array was empty.

By putting in this IF check above, I mitigated the crash.

However,

1. Why exactly does my IF check "work", I see no visual implications of returning the cell before it's been configured. This is confusing

2. Are there any better ways to guard against this happening (ie. the table data being reloaded with an empty array)? Surely the numberOfRowsInSection would have returned array count which would be 0? (if it was an empty array)

EDIT (further code)

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    float count = [self.items count];
    return count;
}

- (void)resetData {
    self.items = [NSMutableArray array];
}

-(void) refreshInvoked:(id)sender forState:(UIControlState)state {
    [self resetData];
    [self downloadHomeTimeline];
    [self.refreshControl endRefreshing];
}

- (void)downloadHomeTimeline {
    [self.apiClient homeTimeline:self.page completionBlock:^(NSDictionary *data){
        for (NSDictionary *obj in data[@"items"]) {
            [self.items addObject:obj];
        }
        [self.itemsTableView reloadData];
    }];
}

Answer 1

I couple of things that i would suggest to do. Make sure that the [self.itemsTableView reloadData] is executed on the main thread and also i would put the [self.refresControl endRefreshing] in the completion block. This way it will stop the refresh when its done and you should not let the user more then once simultaneously.

 - (void)downloadHomeTimeline {
        [self.apiClient homeTimeline:self.page completionBlock:^(NSDictionary *data){
            for (NSDictionary *obj in data[@"items"]) {
                [self.items addObject:obj];
            }
            dispatch_async(dispatch_get_main_queue(), ^{
                [self.itemsTableView reloadData];
                [self.refreshControl endRefreshing];
             }); 

        }];
    }

Also in the numberOfRowsInSection just return count

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [self.items count];
}

To add to the answer. You should not reset the array before you receive new data. While getting new data the user can still scroll the table and that means new cells will be created but your NSMutableArray doesn't have any data. That is when you get the error and app crashes. You would have to [tableView reloadData] to clear the table so that the tableView would know that there are 0 rows, which i don't think is your intent.

Let me know if that's solves the issue.