iOS: DequeTableViewCell..a little bit confused - ios

Question

I want to alter the font size and color etc. for my UITableView cells. I've designed the cells custom in Xcode and got everything working.
First of I'll post my code here:
UITableViewController:
- (void)viewDidLoad
{
[super viewDidLoad];
[self.tableView registerClass:MainCategoryTableViewCell.class forCellReuseIdentifier:#"MainCategoryCell"];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"MainCategoryCell";
MainCategoryTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
return cell;
}
And my custom cell:
- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
if (self) {
self.title.font = [Theme tableCellTitleFont];
self.title.textColor = [Theme tableCellTitleColor];
self.subcategories.font = [Theme tableCellSubTitleFont];
self.subcategories.textColor = [Theme tableCellSubTitleColor];
self.costs.font = [Theme tableCellValueFont];
self.costs.textColor = [Theme tableCellValueColor];
}
return self;
}
I'm confused now how this dequeue works:
As far as I understood if I register the class in the viewDidLoad, the initWithStyle method of the cell gets ONLY called, when theres no cell for reuse. If theres a cell for reuse it will be used. I've seen a lot of if(cell == nil) calls in other code snippets but is that really necessary? I thought the registerClass method takes care of that anyway?
And at the moment my cells will be displayed completely empty. Before I registered the class everything worked, however the initWithStyle didn't get called..
Complete cellForRowAtIndexPathMethod:
#pragma mark Delegate methods
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"MainCategoryCell";
MainCategoryTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
// Configure the cell...
MainCategory *mainCategory = [self.fetchedResultsController objectAtIndexPath:indexPath];
cell.title.text = mainCategory.name;
cell.subcategories.text = [NSString stringWithFormat:#"%i subcategories", [[mainCategory getNumberOfSpendingCategories] integerValue]];
cell.costs.text = [[mainCategory getMonthlyCostsOfAllSpendingCategories] getLocalizedCurrencyString];
if(!mainCategory.icon){
cell.icon.image = [UIImage imageNamed:#"DefaultIcon.png"];
} else {
cell.icon.image = [UIImage imageNamed:mainCategory.icon];
}
if(!mainCategory.color){
cell.backgroundColor = [PresetColor colorForPresetColor:PresetColorsWhite];
} else {
cell.backgroundColor = [PresetColor colorForPresetColor:(PresetColors)[mainCategory.color intValue]];
}
cell.cellBackground.image = [[UIImage imageNamed:#"content-bkg"] resizableImageWithCapInsets:UIEdgeInsetsMake(10, 10, 10, 10)];
return cell;
}

Answer 1

If you have defined the cell as "prototype cell" for the table view in the xib/storyboard file, then you don't have to register it at all. If the custom cell is in a separate nib file, you register the custom cell with registerNib, not registerClass. For example:
[self.tableView registerNib:[UINib nibWithNibName:#"MainCategoryTableViewCell" bundle:nil]
forCellReuseIdentifier:#"MainCategoryCell"];
For cells instantiated from a nib file, initWithCoder is called, not initWithStyle.
To configure any outlets of your custom cell, override awakeFromNib. The connections are
not yet established in initWithCoder.

Answer 2

For best understanding see the below image for just a deque reference.
Deque means you can add and delete cells from both the ends.
By ends I mean up and down.
Lets say you have 4 cell containg Acell,Bcell,Ccell and Dcell and height for row is for three cells.
so at a time only 3 cells would be visible.
when you scroll to see the Dcell , Acell would become as invisible row and memory for it will be reused for Dcell.
In the same way when you scroll to see the Acell , Dcell would become as invisible row and memory for it will be reused for Acell.

Answer 3

It says clearly in documentation
dequeueReusableCellWithIdentifier:forIndexPath:
For performance reasons, a table view's data source should generally
reuse UITableViewCell objects when it assigns cells to rows in its
tableView:cellForRowAtIndexPath: method. A table view maintains a
queue or list of UITableViewCell objects that the data source has
marked for reuse. Call this method from your data source object when
asked to provide a new cell for the table view. This method dequeues
an existing cell if one is available or creates a new one based on the
class or nib file you previously registered.
.
dequeueReusableCellWithIdentifier:
Return Value : A UITableViewCell object with the associated identifier
or nil if no such object exists in the reusable-cell queue.
Discussion : For performance reasons, a table view's data source
should generally reuse UITableViewCell objects when it assigns cells
to rows in its tableView:cellForRowAtIndexPath: method. A table view
maintains a queue or list of UITableViewCell objects that the data
source has marked for reuse. Call this method from your data source
object when asked to provide a new cell for the table view. This
method dequeues an existing cell if one is available or creates a new
one using the class or nib file you previously registered. If no cell
is available for reuse and you did not register a class or nib file,
this method returns nil.
If you registered a class for the specified identifier and a new cell
must be created, this method initializes the cell by calling its
initWithStyle:reuseIdentifier: method. For nib-based cells, this
method loads the cell object from the provided nib file. If an
existing cell was available for reuse, this method calls the cell’s
prepareForReuse method instead.
Before introducing storyboard.The tableview checks the returned cell which can be nil .So if nil we must reallocate the cell and tehn initialize and provide the cell in the datasource method