Objective-C Fundamentals

Important protocols
153
executed. This is the manual instantiation of the cell, which is used only if there’s no
cell to recycle that has recently been scrolled offscreen.
This coding strategy is used in several other places in the iPhone SDK. To show that
the view allocation is working, you make a project with a table view and implement
dequeueReusableCellWithIdentifier just as you see right above. You fill in
tableView: numberOfRowsInSection with the following:
return 100;
You can see the resulting application and its terminal output using the following code:
Insert UITableViewDataSourceTerminalOutput.png and
UITableViewDataSourceProtocolApp
You have 100 cells that you can scroll through here, with 11 active on the screen at any
one time. This means that at the minimum you must create 11 UITableViewCells.
When you look at your terminal output, you can see that 12 UITableViewCells were
created. This is efficient and ensures that as little memory as possible is used to allow
the user to scroll through all 100 cells. This technique is used for memory management
with the protocol as well. Whether you’re using a
UITableViewCell standard class or a custom subclass, this should be your approach to
deliver the cells to the view.
OPTIONAL METHODS
The following method is used when a table view is to have more than one section:
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
When this method isn’t implemented, the method defaults to one. One thing to note
is that the iPhone OS uses a zero-based count for section and row numbers, so the first
element of the first section of a table view will have an index path like the following:
NSIndexPath.row = 0
NSIndexPath.section = 0
The following code is used to set the title of the header for sections when using
default table view headers with the UITableViewStyleDefault:
- (NSString *)tableView:(UITableView *)tableView
titleForHeaderInSection:(NSInteger)section
Every section begins with a header and can also have a footer at the end. If the following
method isn’t defined, there’ll be only headers, no footers, to separate your sections:
- (NSString *)tableView:(UITableView *)tableView
titleForFooterInSection:(NSInteger)section
7.3.2
Unlike the , the has no required
methods. All the methods in this protocol fall into the following functions: