Displaying a "No rows found" message in UITableView with Core Data

Question

I have implemented an iPhone app that uses UITableViewController/UITableView and Core Data. Further, I use a NSFetchedResultsController to manage the table data. This was all very straight forward and works great. I then decided that I should display a message in the UITableView when no rows where found/retrieved. After researching this, it appeared that the best way (perhaps the only way) to do this was to return a "dummy" cell that contains the message. However, when I do this, I get a nastygram from the runtime system that complains (and rightfully so) about data inconsistencies: "Invalid update: invalid number of sections. The number of sections contained in the table view ...". Here is the relevant code:

- (NSInteger) numberOfSectionsInTableView: (UITableView *)tableView
{
    if ([[self.fetchedResultsController fetchedObjects] count] == 0) return 1;
    return [[self.fetchedResultsController sections] count];
}

- (NSInteger) tableView: (UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    if ([[self.fetchedResultsController fetchedObjects] count] == 0) return 1;
    id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex: section];
    return [sectionInfo numberOfObjects];
}

- (UITableViewCell *) tableView: (UITableView *)tableView cellForRowAtIndexPath: (NSIndexPath *)indexPath
{
    if ([[self.fetchedResultsController fetchedObjects] count] == 0) {
        UITableViewCell *cell = [[UITableViewCell alloc] init];
        cell.textLabel.text = @"No widgets found.";
        return cell;
    }

    STCellView *cell = (STCellView *)[tableView dequeueReusableCellWithIdentifier: @"ShieldCell"];
    [self configureCell: cell atIndexPath: indexPath];
    return cell;
}

I have read responses from similar questions and it appears that I should use

insertRowsAtIndexPaths: withRowAnimation:

to insert the "dummy" message row into my table. However, this also means removing the "dummy" row when a real row is inserted. I can do this, but it seems like there should be an easier way to accomplish this. All I want to do, is to display a message indicating that there are no rows in the table (simple enough?). So, my question is this: Is there a way to display a message in an UITableView without using the "dummy" cell approach OR is there a way to convince UITableViewController/NSFetchResulsController that this is only a "dummy" row and they should not get so upset about it because it is not a real row (from my point of view) in the table?

Any help you can provide would be very appreciated (I am a struggling newbie to iPhone development and I want to learn the best practices). Thanks.

Answer 1

Rather than hack with the tableview datasource to get the intended UI you should add the "No rows found" message to the tableview header instead.

Answer 2

I did as follows in viewDidLoad.

UILabel *label = [[UILabel alloc] init];
[label setTextColor:[UIColor lightGrayColor]];
[label setText:@"No widgets found."];
[label sizeToFit];
label.frame = CGRectMake((self.tableView.bounds.size.width - label.bounds.size.width) / 2.0f,
                         (self.tableView.rowHeight - label.bounds.size.height) / 2.0f,
                         label.bounds.size.width,
                         label.bounds.size.height);
[self.tableView insertSubview:label atIndex:0];

In this case, each TableViewCells must be opaque to hide the label. or need to toggle the hidden property of the label according to the row count.