n o t e 1 9 . c o m

In HTML colors are typically specified in a HEX format, where each color is a number from 0 to 255 represented as a two digit hex number. For example, the aqua blue shade color is represented as 0095D2, where the value for Red is 00, the value for Green is 95 and the value of Blue is D2. For iPhone development, the colors are specified in RGB float where each of the RGB colors is a number between 0.0 to 1.0.

In core-plot, you can add your own colors via Objective-C category construct from within any of your own header and implementation files.

@interface CPColor (AQ_COLOR)
 +(CPColor *)aq_blue_color; // #0095D2 
@end

@implementation CPColor (AQ_COLOR)

+(CPColor *) aq_blue_color { 
    static CPColor *color = nil;
    if ( nil == color ) {
		color = [[CPColor alloc] initWithComponentRed:(0x00&0xff)/255.0 green:(0x95&0xFF)/255.0 blue:(0xD2&0xFF)/255.0 alpha:1.0];
    }
	return color; 
}
@end

Now you can use this color to fill a bar chart, e.g.

barPlot.fill = [CPFill fillWithColor:[CPColor aq_blue_color]];

There is no built-in drop down list in iPhone SDK. You’ll need to create the interaction from the combination of the Picker and some other control, e.g., a button. Here are the steps to create and initialize a UIPickerView for all the 50 States:

Start Interface Builder and drag a Picker View object from the Library tool to the View object. This will create a UIPickerView object for you. Alternatively you can programmatically create this object in Xcode. But it is easier to use the IB. If you now build and run your project, you wont see the picker. To see it you’ll need to set the data source and delegate.

In IB, control-click on the Picker and then drag and connect the dataSource and delegate outlets to the File’s Owner for the view controller. Now if you build and run your application, you’ll see an empty picker. The control-click on the picker is a short cut for connecting the data source and the delegate properties. In addition, you’ll need to connect the picker to your view controller to create the object so that you can access it in Xcode. You do this by dragging the New Referencing Outlet from the IB’s Picker VIew Connection to the File’s Owner object in the xib file view. Alternatively, when you control-click, you can drag a New Referencing Outlet from the popup.
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In JavaScript, it is fairly easy to add a button and its event handlers. HTML and the browser are your Interface Builder and your text editor is your Xcode. There is no need to graphically connect anything and there is no confusion where you add the button and where you add the event handlers. For iPhone programming, the model is more sophisticated and hence it is more complicated to nail the basics. So how do you add a simple button and its event handler in Objective-C and iPhone SDK?

Typically you will want to add a button using the Interface Builder and then add the button’s event handlers in Xcode. Here are the steps:

1. In Xcode double click on the NIB file that defines the view to which you wish to add a button. This will start the Interface Builder (IB).
2. In IB, open the Library tool and drag a button to the view. Position and resize this button and give it a title.
3. Now you need to connect the button to the View Controller class so that you can control and customize this button from Xcode. You can control-click on the button and drag the connection line to the File’s Owner in the xib view (alternatively, you can start the IB’s Inspector, select the Button Connection tab and create a Referencing Outlet – drag the connection similar to before).
4. In Xcode you’ll need to define the button to the view controller’s interface file and then define the methods to customize the button and define its events handlers.

In this sample, I’ve added a UILabel and a UIButton class so that when you click on the button the value of the label is changed.

@interface TestViewController : UIViewController {
	IBOutlet UILabel *mylabel;
	IBOutlet UIButton *mybutton;
}
@property (nonatomic, retain) UILabel *mylabel;
@property (nonatomic, retain) UIButton *mybutton;
@end

In the implementation file, you need “synthesize” the label and button objects.

@implementation TestViewController

@synthesize mylabel;
@synthesize mybutton;

Next I try to customize the label on the button and add an event handler.

- (void)viewDidLoad {
        [super viewDidLoad];
	mylabel.text = @"www.aquacue.com";
	[mybutton setTitle:@"Aquacue - Normal" forState: (UIControlState)UIControlStateNormal];
	[mybutton setTitle:@"Aquacue - Highlighted" forState: (UIControlState)UIControlStateHighlighted];
	[mybutton addTarget:self action:@selector(myButtonClick:) forControlEvents:(UIControlEvents)UIControlEventTouchDown];
}

Now here is the definition of the handler:

-  (void)myButtonClick:(id)sender {
	mylabel.text = @"Clicked";
}

Next I add another event handler so that when you click on the screen background, the value of the label is changed:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    mylabel.text = [NSString stringWithFormat: @"Hello Aquacue %@ %d", @"AAA", event.timestamp];
    [super touchesBegan:touches withEvent:event];
}

You can also use the IB to define event handlers (aka Actions). The easiest way is to actually define the handler/action in Xcode using the IBAction declaration in the interface file (add the declaration just before the @end statement).

- (IBAction)myButtonPressed:(id)sender;

Next you’ll need to define the myButtonPressed handler in the implementation file:

- (IBAction)myButtonPressed:(id)sender {
	mylabel.text = @"Change the label, when user clicks on the button";
}

Note that in this sample, I’ve defined two handlers one using the UIButton addTarget method and another using the IBAction. Both of these handlers are called when the user clicks on the button. As it turns it both of these handlers get called IBAction gets called first followed by the handler that was added via addTarget.

Only the methods defined with the IBAction declaration are exposed to the IB. You can control-click on the button object in IB and you’ll see a popup menu that defines all of the events that the object is willing to handle. Using the normal IB way, you’ll need to drag an event to the File’s Owner object to expose the event handler in Xcode.

I’ve started learning objective-C for my iPhone SDK programming project and was wondering how to concatenate strings and integers, … I saw a number of posts on the web about how verbose Objective-C is compared to C#. No mention was made that C# arrived 20 years after  Objective-C and it was a poorer version of Java. Anyhow, want to concatenate a bunch of primitive types as a string? Here is what you do (recall your sprintf syntax)

[NSString stringWithFormat: @"Hello Aqua %@ %d", @"cue ", 1];

For string concatenation, Objective-C is almost as concise as Perl -)