UITableView reloadData doesnt reload the table but UITableView reloadSections work - ios

Question

I have a UITableView embedded inside a parent UIView. I have a CustomUITableViewController class set as delegate and datasource for the tableview.
After a certain background operation, I get an updated array of objects to be displayed in the tableview.
When I update the datasource array and call tableview.reloadData method, the tableview doesn't refresh. It only refreshes if I scroll the tableview.
However, if I call the API as follows:
tableview.beginUpdates -> tableview.reloadSections -> tableview.endUpdates,
it works perfectly and immediately reloads the table.
The problem is that depending on the new data, I have to add a new section, or remove an old section from the tableview.
Hence I am not able to use the reloadSections API.
Any thoughts on how to fix this?
Code:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *cellID = #"tempCell";
CustomCell *cell = [tableView dequeueReusableCellWithIdentifier:cellID];
if (cell == nil) {
cell = [[CustomCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellID];
}
[cell initializeWithModel:modelsToShow[indexPath.row]];
return cell;
}
-(void) showModelsInList:(NSMutableArray*) models {
[modelsToShow removeAllObjects];
[modelsToShow addObjectsFromArray:models];
[self setupDataForList];
[self reloadTable];
}
-(void) reloadTable {
[self.tableView beginUpdates];
NSMutableIndexSet* index = [[NSMutableIndexSet alloc]init];
[index addIndex:0];
[self.tableView reloadSections:index withRowAnimation:UITableViewRowAnimationFade];
[self.tableView endUpdates];
//[self.tableView reloadData]
}
The showModelsInList method is invoked from the other class, in the main thread itself.

Answer 1

The modern way to initialize table view cells is to register the cell class (or nib, if the cell is defined in its own nib). viewDidLoad is a good time to do this...
// if the cell is a prototype defined in the nib containing the table view, or if
// the cell is built in code in its init method
[self.tableView registerClass:[CustomCell self] forCellReuseIdentifier:#"tempCell"];
// or, if the cell is defined in its own nib
UINib *nib = [UINib nibWithNibName:#"your cell's nib name goes here" bundle:nil];
[_tableView registerNib:nib forCellReuseIdentifier:#"tempCell"];
In either case above, the cell must have it's "tempCell" identifier initialized in IB or in code. Then, in cellForRowAtIndexPath, dequeue the cell using the method...
CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:#"tempCell" forIndexPath:indexPath];
No further check is required to see if (cell == nil). This version of dequeue will just work (or crash, if something's not setup correctly).

Answer 2

I think, technically, it's a bug, but the truth is that, though it's not documented, you shouldn't be recreating subviews in cellForRowAtIndexPath when reusing cells.
Create the cells with all needed subviews at design time in Interface Builder. Changing their positions, sizes, and other properties in cellForRowAtIndexPath is okay.
If your cells have different subviews, each cell "type" should be its own class. Create a different prototype cell class with a different identifier for each, and simply use that identifier when you dequeue the cell. That way, you have the proper cell class in cellForRowAtIndexPath.
To reference additional properties (subviews) from your view controller, simply create class files for each cell type (derived from UITableViewCell). Assign it to the prototype UITableViewCell in IB, drag the views to the .h file to create outlets like you do for a view controller, then import that class in your view controller.
So, you might end up with code like this:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
if (whatever) {
MyBasicCell *cell = [tableView dequeueReusableCellWithIdentifier:#"basicCell"];
cell.specialLabel.Text = ...
return cell;
} else {
MyOtherCell *cell = [tableView dequeueReusableCellWithIdentifier:#"otherCell"];
cell.otherLabel.Text = ...
return cell;
}
}