First off before we start, here are a couple of things you will need to get started:
1. Mac running the latest version of xcode – This can be found on your install disc for leopard or snow leopard.
2. Latest version of the iphone SDK – This can be found at developer.apple.com
Now we can get started. Once you have xcode and the iphone SDK installed, open up xcode(Macintosh HD > developer > Applications). Once you have xcode installed, from the menu bar select file > new project. You should see a windows like the this one.
Select window based application from the iphone application option on the left hand side of the window. Once you select the window based application, xcode will prompt you to save the project. I named my project “LabelTester” and saved it under my personal iphone projects directory. Once you save the project, an xcode window should open up and look something like this.
You should see a combination of files here in the browser in the code browser. The first should be the CoreGraphics.framework. This is just a set of files provided by Apple that have all the code relevant to the core graphics libraries in Cocoa. The second is the foundation.framework. This is the library set for the foundation framework which is basically all the classes like NSArray, NSString and other foundation objects. The next item should be LabelTester.plist. The plist, or preference list, is a set of XML attributes that control how the application is handled. For the sake of this tutorial, you won’t need to open the plist. The next item should be the LabelTester.app file, which is the executable for your application. Once your application is deployed, all files and resources in your project will be located inside your app’s .app file. The next file is the LabelTester.pch file. This file is the prefix header for your application. The LabelTesterAppDelegate.h file is the next file in the list. This file is the header file for your application delegate. This is the starting for your application, the app delegate is what’s run by your main.m file when you app is launched. The .h file is of course the header file, which is basically the interface file that the .m file will implement. The next file is of course the LabelTesterAppDelegate.m. This file is the implementation file for the app delegate header. Next is the main.m file. This file is the application launcher for your app. It basically runs the app delegate. The next file is the Main Window.xib file. Anything with a nib/xib file extension is classified as an interface builder file and you open these files in the Interface builder application. Finally, the UIKit.framework. This library is used to correspond to all the UI elements on the iphone(text fields, buttons, etc).
Let’s start by opening up our Main Window.xib to setup our interface. Start by dragging a button from the libraries window onto your main View. Rename that button by double clicking on the button and change it to say “Update Label!”. Next, grab a text field and drag it just above the button. Expand the text field to fit the majority of the screen. Select the textfield and go into the attributes tab and enter into the placeholder field, “Enter Text to update Label”. Once that’s finished, drag a label onto the main window and change the text from “label” to “Label to Update”. Once that’s done you can save the interface builder file by pressing (command + s) and switch your view back to your xcode project.
Open up the LabelTesterAppDelegate.h file and change the file to reflect the following code.
#import
@interface LabelTesterAppDelegate : NSObject
{
UIWindow *window;
IBOutlet UITextField *textField;
IBOutlet UIButton *button;
IBOutlet UILabel *label;
IBAction *updateButtonPressed;
}
@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet UITextField *textField;
@property (nonatomic, retain) IBOutlet UILabel *label;
-(IBAction)updateButtonpressed:(id) sender;
@endThe first lines inside the curly braces will declare variables that we will be hooking up in Interface builder later. After the curly braces are closed, we have these property tags. These will allow us to have access to the objects and their data in the implementation file. After that we have an IBAction method declaration. This will eventually be hooked up to our button to run every time that our button is pressed. You can think of an IBAction method as an event handler in OBjective-C. Now let’s move onto our LabelTesterAppDelegate.m file and add the following method directly below out import statement.
#import "LabelTesterAppDelegate.h"
@implementation LabelTesterAppDelegate
@synthesize window;
@synthesize textField;
@synthesize label;
-(IBAction)updateButtonpressed:(id) sender
{
//allocate a string and initialize it with the data from the text field
NSString *string = textField.text;
label.text = string;
}Basically what we’re doing here is just creating that IBAction method that we declared in our interface file. Inside that method, we allocate a string to the value of our textField.text and then set the label equal to the string that we get from the textfield. That’s all the code we’ll need for now. Don’t forget to synthesize your objects below the implementation declaration in order to have access to the data you want. If you try and run this now, the application will run but will not function because the pointers in Interface Builder are not hooked up. So let’s go ahead and do that next. Save all your xcode files and open back up your Main Window.xib file in Interface Builder.
In order to setup a pointer in Interface builder, start by clicking on the application delegate and then the connections manager should appear. Beside each of the items that you created you should see a tiny circle. For each, click on the circle and drag the pointer to each of the elements in your window. This will create a pointer to that element. Now click on the button and then open it’s connection manager. Find the “touch up inside” connection and drag that pointer to the “file’s owner” section in the library and select “updateButtonPressed” when it appears. Once this is completed, you should see the connection screen look something like this.
That’s all folks, now if you run the application and enter some text into the text field, it will update the label to whatever text you entered. To download the whole project click here.
Cheers everyone and stay tuned for part 2!
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