iPhone: UITableView not refreshing - iphone

Question

I have read many topics about UITableViews not refreshing on iPhone, but couldn't find anything matching my situation, so I'm asking for help.
In my class, which extends UIViewController, I have a TableView and an 'ElementList' (which is a wrapper for NSMutableArray) used as data source.
A separate thread adds a new Element to the array via the 'updateList:' method.
When this happens, I want the tableView to be refreshed automatically, but this doesn't happen.
By debugging my app, I can see that 'cellForRowAtIndexPath' is never called and I can't figure out why.
I tried to add an Observer, which calls the 'reloadTableView' method (it is actually called) but the tableView is not updated.
This is my code:
#import <UIKit/UIKit.h>
#interface ListViewController : UIViewController <UITableViewDelegate, UITableViewDataSource>
{
UITableView *tableView;
ElementList *elementList; // Wrapper for NSMutableArray
}
// Called by someone else, triggers the whole thing
-(void)updateList:(Element *)element;
// Added out of desperation
-(void)reloadTableView;
#end
#implementation ListViewController
-(void)loadView
{
// Create the TableView
tableView = [[UITableView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame] style:UITableViewStylePlain];
assert(tableView != nil);
tableView.delegate = self;
tableView.dataSource = self;
[tableView reloadData];
self.view = tableView;
// Added out of desperation
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(reloadTableView) name:#"UpdatedListNotification" object:nil];
}
-(void)reloadTableView
{
// Try anything
[tableView reloadData];
[tableView setNeedsLayout];
[tableView setNeedsDisplay];
[tableView reloadData];
[self.view setNeedsLayout];
[self.view setNeedsDisplay];
}
// Called by someone else, triggers the whole thing
-(void)updateList:(Element *)element
{
assert(element != nil);
[elementList addElement:element];
[element release];
// Notify the observer, which should update its table view
[[NSNotificationCenter defaultCenter] postNotificationName:#"UpdatedListNotification" object:self];
}
// TableView Delegate protocol
- (void)tableView:(UITableView *)table didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
Element *selected_element = [elementList getElementAtIndex:indexPath.row];
if (selected_element == nil)
{
NSLog(#"ERROR: Selected an invalid element");
return;
}
[table deselectRowAtIndexPath:indexPath animated:YES];
NSLog(#"Selected %#", selected_element.name);
}
// TableView Data Source protocol
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [elementList count];
}
- (UITableViewCell *)tableView:(UITableView *)table cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [table dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil)
{
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
// Set the cell label
cell.textLabel.text = [[elementList getElementAtIndex:indexPath.row] name];
cell.textLabel.frame = cell.bounds;
cell.textLabel.textAlignment = UITextAlignmentLeft;
return cell;
}
#end
Any help is greatly appreciated, thank you.

Answer 1

Notifications are executed in the same thread as the caller. Updating the UI should really be done in the main thread, so you should call -reloadData on the main thread:
-(void)updateList:(Element *)element
{
assert(element != nil);
[elementList addElement:element];
[self.tableView performSelectorOnMainThread:#selector(reloadData) withObject:nil];
}
Also note that you shouldn't release an object that you don't own. So don't call [element release] in your -updateList method. The release should be called by the caller of the function.

Answer 2

That didn't quite work for me - but very close. The method I used was -
[self.tableView performSelectorOnMainThread:#selector(reloadData) withObject:nil waitUntilDone:YES];

Answer 3

You can also do
[self performSelectorOnMainThread:#selector(reloadTable) withObject:nil waitUntilDone:YES];
so that you can implement a method on the ViewController to do all the UI stuff that you need.
-(void)reloadTable
{
[self.tableView reloadData];
}