How do I access my array from my table data source? - objective-c

Question

I am starting my first Cocoa Project. And I have a serious (for me) but maybe easy problem (for you) to solve and I need some direction where to start.
The short description: I have built a class "PortConnection.h" who writes all ports found by an external class (AMSerial.h) into an array when the function -listPorts is called. Here is the code for the PortConnection.h
#import <Cocoa/Cocoa.h>
#import "AMSerialPortList.h"
#import "AMSerialPortAdditions.h"
#import "AMSerialPort.h"
#interface PortConnection : NSObject {
#private
AMSerialPort *port;
NSMutableArray *portArray;
}
- (void)listDevices;
#property (nonatomic, retain) NSMutableArray *portArray;
#property (nonatomic, retain) AMSerialPort *port;
#end
and following the PortConnection.m
#import "PortConnection.h"
#import "AMSerialPortList.h"
#import "AMSerialPortAdditions.h"
#import "AMSerialPort.h"
#implementation PortConnection
#synthesize portArray;
#synthesize port;
- (void)listDevices
{
// get an port enumerator
NSEnumerator *enumerator = [AMSerialPortList portEnumerator];
AMSerialPort *aPort;
while ((aPort = [enumerator nextObject]))
{
// Add Devices to Array
[portArray addObject:[aPort bsdPath]];
}
}
So far it is perfectly working.
Now my questions
I have implemented an tableView in the GUI for display the results of the method called above. This file is called "PortTableViewController.h" and is the datasource for my TableView.
Here is the .h file
#import <Foundation/Foundation.h>
#import "PortConnection.h"
#interface PortTableViewController : NSObject <NSTableViewDataSource> {
#private
IBOutlet NSTableView *portTableView;
}
#property (assign) IBOutlet NSTableView *portTableView;
#end
and here is the .m file:
#import "PortTableViewController.h"
#import "PortConnection.h"
#implementation PortTableViewController
#synthesize portTableView;
#pragma mark -
#pragma mark TableView Delegates
- (NSInteger)numberOfRowsInTableView:(NSTableView *)tableView{
PortConnection *portConnection = [[PortConnection alloc] init];
[portConnection listDevices];
return [portConnection.portArray count];
}
- (id)tableView:(NSTableView *)tableView objectValueForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row{
??????? I DO NOT HAVE A CLUE HOW TO ACCESS THE ARRAY IN PORTCONNECTION.M CORRECTLY
}
#end
QUESTIONS:
1) When having a look on the TableViewDataSourceDelegates how do I access the filled portArray in the PortConnection.m class correctly. It doesn't seem to work the way I do it.
2) Do I have to create an Object from Portconnection.h every time I want to retrieve Data from it in a tableviewdelegate method?
I am really thankful for every kind of help! I want to learn something.. and I really appreciate your support! Thanks.. for question in order to help me, don't hesitate. I really appreciate it....
Thanks
Sebastian

Answer 1

A simple fix is to have your table view controller declare an instance variable that holds a PortConnection instance. This instance is created and sent -listDevices in -init, it is used by all methods in your table view controller (which means that all methods refer to the same PortConnection instance), and released in -dealloc.
For example:
PortTableViewController.h
#import <Foundation/Foundation.h>
#import "PortConnection.h"
#interface PortTableViewController : NSObject <NSTableViewDataSource> {
#private
IBOutlet NSTableView *portTableView;
PortConnection *portConnection;
}
#property (assign) IBOutlet NSTableView *portTableView;
#end
PortTableViewController.m
#import "PortTableViewController.h"
#import "PortConnection.h"
#implementation PortTableViewController
#synthesize portTableView;
#pragma mark -
#pragma mark TableView Delegates
- (id)init {
self = [super init];
if (self) {
portConnection = [[PortConnection alloc] init];
[portConnection listDevices];
}
return self;
}
- (void)dealloc {
[portConnection release];
[super dealloc];
}
- (NSInteger)numberOfRowsInTableView:(NSTableView *)tableView{
return [portConnection.portArray count];
}
- (id)tableView:(NSTableView *)tableView objectValueForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row{
return [portConnection.portArray objectAtIndex:row];
// or whatever behaviour provides an object value for the column/row
}
#end

Answer 2

If you don't want to create a field in every delegate you could create a static variable in PortConnection which holds the array. Initially the array is nil and on the first call to get the ports you create the list if needed.
In the implementation file:
static NSMutableArray *portArray;
+ (NSArray) listPorts {
if(portArray != nil)
return (NSArray *)portArray;
NSEnumerator *enumerator = [AMSerialPortList portEnumerator];
AMSerialPort *aPort;
portArray = [[NSMutableArray alloc] init];
while ((aPort = [enumerator nextObject])) {
// Add Devices to Array
[portArray addObject:[aPort bsdPath]];
}
}
This of course depends on how often the portArray will change, if it's often I would probably just generate it every time.
You could also do a getPortArray which calls generatePortArray if portArray is nil

Answer 3

You should only need a single PortConnection instance, but your table view controller will somehow need to know about it. It could be that the PortTableViewController creates and owns the PortConnection object, or it could be that some other object, like the app delegate or another controller creates it.
In the former case, it's trivial... the PortTableViewController creates the PortConnection instance, and therefore it has a reference to it and can access its portArray property at well.
In the latter case, things aren't much more complicated: the object that creates the PortController should give the PortTableViewController a pointer to the PortController. The PortTableViewController should then retain the PortController and stash the pointer in an instance variable so that it can access the portArray property as needed.