Wired Up And Fired Up

So, what we are going to build is a simple application that populates a table column with random numbers, the column will be sortable by clicking on the column header (default behavior for OS X). The intention is to show how easily this can be achieved using Cocoa/Objective-C and not as an introduction to the Objective-C language or the Cocoa Frameworks.

The first thing to do is create a new XCode Cocoa project. So, in XCode we choose File from the menu, then New Project... and from the list pick 'Cocoa Application'. Give it a suitable name (e.g. Sort Columns).

XCode will create most of the stuff we'll need to get going, in fact if you click on 'Build and Go' you'll see an empty window and the menu for your new application appear. You should notice that it already has quite a bunch of functionality, try choosing Print from the File menu of your Application...

Neat, eh? Right, now lets get our hands dirty with some code - don't worry though there's, like, 20 lines of it.

We'll need to create a class that represents our data, in this case a number. When it is created it will be populated by random and will have two methods; one to get the value of the number and one to change it. These types of methods are commonly called accessors or mutators, as they allow you to access or change the data stored in a class.

Create a class in XCode by chosing File-> New File... and then selecting Objective-C Class from the list of file types. Call it TableThing.

You'll see XCode has created two files, TableThing.h the interface and TableThing.m the implementation.

Change TableThing.h to read:

#import <Cocoa/Cocoa.h>
#import <Foundation/Foundation.h>

@interface TableThing : NSObject {
float aNumber;
}

-(float)aNumber;
-(void)setANumber: (float)newNumber;

@end


And TableThing.m to read:

#import "TableThing.h"

@implementation TableThing

-(id)init{
[super init];
[self setANumber: (random() % 100) + 1];
return self;
}

-(float)aNumber;{
return aNumber;
}

-(void)setANumber: (float)newNumber;{
aNumber = newNumber;
}

-(void)dealloc{
[super dealloc];
}

@end

That's all the code we're going to write. With the new properties shortcuts in Objective-C 2.0 even this will be reduced. Next, we'll plumb in the UI, in your XCode project there will be a file called MainMenu.nib, double click it to open it in Interface Builder.

Once in Interface Builder open the Window and add the following controls to it, an NSTableView and two NSButton instances. (I also added a label for clarity.)



Once your window looks something like this we can wire it all together. The next thing to do is to drag an NSArrayController into the MainMenu.nib window, as shown below.



Now we'll need to set the NSArrayController up to actually control something, in our example it'll control an array of TableThing objects, so in order to set it up to do that we need to set the Class Name and Keys in the NSArrayController's inspector. To pull up the inspector select the controller and press Option-Shift and 'i', set the Class Name to TableThing and add a key for the aNumber property of the TableThing class as shown below.



Ok, now we can wire in the buttons. You can do this by ctrl-dragging from the button to the NSArray controller.



Set the Target/Action for the 'new' button to 'insert' and do the same for the 'remove' button but set it's target to 'remove'.

Next double click on the table column itself and pull up it's inspector (option-shift-i) and in the bindings pane set the value settings as below -



There, nearly done. Now there's just sorting to add, this is implemented in it's entirety in the Attributes pane of the NSTableColumn Inspector.



That's it! Build and run the application, press 'new' a few times to fill up the table with random numbers and then sort them by clicking on the title bar of the column.

To get this working even more quickly, you can download the source here.

I hope this post demonstrates how easy it is to get going with Cocoa development and how much functionality you simply get 'For Free' using it. For the sake of brevity I deliberately wrote a lot on the 'how's and not much on the 'why's and 'what's of what we were doing, however, if this is something people are interested in I could quite happily write a few more in-depth tutorials.