Where are the UITableViewCell's initialized? - ios

Question

I've created my own CustomTableView and CustomCell. The cell is in a xib, and I'm registering it when initializing the tableView, like this:
[self registerNib:[UINib nibWithNibName:#"CustomCell" bundle:nil]
forCellReuseIdentifier:kCustomCellIdentifier];
If I don't do this, I won't be able to define what ReuseIdentifier should "point" to this class. This is my cellForRow:
-(UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
CustomCell *cell = [self dequeueReusableCellWithIdentifier:
kCustomCellIdentifier forIndexPath:indexPath];
if(!cell)
{
cell = [[[NSBundle mainBundle] loadNibNamed:#"CustomCell"
owner:self options:nil] objectAtIndex:0];
cell.delegate = self;
[cell initialSetup]; //Other stuff
}
else
[cell resetCell];
//And other awesome stuff
return cell;
}
This 'works'. When I lauch my app, my own custom cells are showing.
However, it turns out the cell is NEVER returned as nil from [self dequeue... Thus, the if-statement if(!cell) is never true. I have additional setup inside this statement that I want to perform, but I don't know where the cell's are being initialized the first time now. If I remove registerNib, then this statement is true, but then it's true for all cells, and none will ever be dequeued.
I can probably work around this, and put my initialSetup (and other stuff) inside the -(id)initWithCoder..-method in the CustomCell-class, but I'd like to know where my cells are being initialized right now. Why do my cells exist before cellForRowAtIndexPath?

Answer 1

When you register a class or a nib in a table view using method registerClass:forCellReuseIdentifieror registerNib:forCellReuseIdentifier the tableview internally will create an instance of the cell if no one is available when you call dequeueReusableCellWithIdentifier:, so initialization code is no longer needed inside the delegate.
From the UITableView.h code:
// Beginning in iOS 6, clients can register a nib or class for each cell.
// If all reuse identifiers are registered, use the newer -dequeueReusableCellWithIdentifier:forIndexPath: to guarantee that a cell instance is returned.
// Instances returned from the new dequeue method will also be properly sized when they are returned.
- (void)registerNib:(UINib *)nib forCellReuseIdentifier:(NSString *)identifier NS_AVAILABLE_IOS(5_0);
- (void)registerClass:(Class)cellClass forCellReuseIdentifier:(NSString *)identifier NS_AVAILABLE_IOS(6_0);
Depending of the which register method is used the init methods called are:
initWithStyle:reuseIdentifier for cells registered using registerClass:
initWithCoder: for cells registered using registerNib:
If you are using registerNib: you can use too awakeFromNib method in the cell, that is also a good place to put initialization code of the cell. The main difference between using initWithCoder: or awakeFromNib its explained in this question.
When a cell is reused, you have the method prepareForReuse in the cell to make some cleanup in the cell and left it prepared to be configured again.
A good approach to work with all of this will be:
//ViewController code
- (void)viewDidLoad
{
...
[_tableView registerNib:[UINib nibWithNibName:#"CellSample" bundle:Nil] forCellReuseIdentifier:#"cellIdentifier"];
...
}
- (UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:#"cellIdentifier"];
//configure the new cell, no if (!cell) needed
return cell;
}
//Cell code
- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super initWithCoder:aDecoder];
if (self) {
//You can put initialization here
}
return self;
}
- (void)awakeFromNib
{
[super awakeFromNib];
//But is better initialize here
}
- (void)prepareForReuse
{
//Reuse and reset the cell here
}
Hope it helps

Answer 2

When using dequeueReusableCellWithIdentifier: forIndexPath: you don't have to alloc the cell like you would if you were using default UITableViewCell. In your custom UITableViewCell subclass, this is called when it is initialized:
- (void)awakeFromNib {
[super awakeFromNib];
}
So add that in there and you should be good.

Answer 3

- (instancetype)initWithStyle:(UITableViewCellStyle)style
reuseIdentifier:(NSString *)reuseIdentifier{
self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
if (self) {
//custom your cell
}
return self;
}