Table View Returning Funny Error - iphone

Question

Okay I am creating a Table View using objective c, but the data source is not working correctly...
My error:
2012-06-02 20:14:39.891 Dot Golf Scoring[195:707] *** Assertion failure in -[UITableView _createPreparedCellForGlobalRow:withIndexPath:], /SourceCache/UIKit/UIKit-1914.85/UITableView.m:6061
2012-06-02 20:14:39.895 Dot Golf Scoring[195:707] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'UITableView dataSource must return a cell from tableView:cellForRowAtIndexPath:'
My Code:
-(NSInteger) numberOfSectionsInTableView:(UITableView *)tableView {
return 1;
}
-(NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return 16;
}
-(NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
return #"Comments On Your Round";
}
-(UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"Cell"];
cell.textLabel.text = #"Text Label";
return cell;
}
Why is the table view not getting filled with this fake data???

Answer 1

You are never initializing cell. Use this code:
- (UITableViewCell *)tableView:(UITableView *)tableView2 cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell *cell = [tableView
dequeueReusableCellWithIdentifier:#"UITableViewCell"];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:#"UITableViewCell"]
autorelease];
cell.textLabel.text = nil;
}
if (cell) {
//customization
cell.textLabel.text = #"Text Label";
}
return cell;
}
You say you are a noob.... let me explain
First of try picking up the book:
The Big Nerd Ranch Guide
What you are thinking is that dequeueing is basically initializing right? NO! Dequeuing is basically nilling any cell that is not visible, aka you scroll past it. Therefore, cell == nil will be called in probably four situations (that I can think of):
When we first setup the table view (cells will be nil)
When we reload data
Whenever we may arrive at this class
When the cells becomes invisible from the table view
So, the identifier for dequeuing is like an ID. Then in the statement to see if cell is nil, we initialize cell, you can see the overridden init method: initWithStyle. This is just what type of cell there is, there are different types with different variables you can customize. I showed you the default. Then we use the reuseIdentifier which was the dequeuing identifier we said earlier. THEY MUST MATCH! I nil textLabel just for better structure, in this case each cell has the same text so it won't matter really. It makes it so the cell that dequeues comes back with the right customization you implemented. Then once cell is actually valid, we can customize.
Also, you are using the same text for each cell. If you do want to have different text for each cell, familiar yourself with NSArray. Then you could provide the array count in numberOfRowsForSection and then do something like this:
cell.textLabel.text = [array objectAtIndex: [indexPath row]];
Where indexPath is the NSIndexPath argument provided in the cellForRowAtIndexPath method. The row variable is the row number, so everything fits!
Wow, that was a lot to take in right!
Now go stop being an objective-c noob and start reading some books!
For more info read:
Table View Apple Documentation

Answer 2

I don't think you read the Table View Programming Guide or understood the reuse mechanism of UITableViews ;)
Cells in UITableViews are reused/recycled, to avoid reallocating an instance of the UITableViewCell class each time you need a cell. This is because UITableView needs a lot of reactivity, especially when scrolling the tableview as the scrolling needs to be fast, and allocating a new UITableViewCell instance each time would make the tableview hang for a second while the instance is created.
So the idea behind UITableViewCell reuse mechanism is to allocate the minimum amount of cells, and each time you need a cell, try to reuse/recycle a cell that was previously allocated but is no longer user (because it is offscreen since you scrolled).
But if there is no cell available to reuse, you need to allocate one yourself!.
You forgot to do this part in your code, that's why you end up returning a nil cell, which throws the exception.
So the typical code to do this is :
static NSString* kCellId = #"Cell";
// First, try to reuse a cell that was previously allocated
UITableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:kCellId];
// here, if a cell is returned, that means that we have an old cell
// that was used before but is no longer onscreen (so we can recycle it
// and just actualize its content)
// but if cell is nil, this means the UITableView didn't have a cell available to reuse
// so we need to create a new one
if (cell == nil)
{
// So if we didn't have a old cell ready to reuse that have been returned, create one
cell = [[[UITableViewCell alloc] initWithReusableIdentifier:kCellId] autorelease];
// And configure every properties of the cell that will be common to every cell
// and won't change even if the cell is recycled, eg:
cell.textLabel.textColor = [UIColor redColor];
cell.textLabel.font = [UIFont boldSystemFontOfSize:12];
// etc
}
// And at this point, we have a cell, either newly created or that have been recycled
// So we configure every property that is row-dependant and change for each row, eg:
cell.textLabel.text = [myTextsArray objectAtIndex:indexPath.row];
NB: I never used storyboard but AFAIK, when you use storyboard, you don't need to have the "if" statement and create the cell when no reusable cell is avaiable, as storyboard will create it for you using the cell design in your storyboard. But this is the only case when you don't need to allocate the cell youself.