The first function is called when the startButton is pressed. If the text of the button is Start, then we want to disable the resetButton, change the startButton's text to Stop mark the startTime, and instantiate the timer callback. If the text of the startButton is not Start, then we want to enable the resetButton, disable the startButton, and invalidate the timer callback funtion.

The second function handles the resetButton. If the resetButton's been pressed, the timeLabel is reset to 00:00:00.0, the startButton text is set to Start and enabled, and the resetButton is disabled.

Finally, we have a function to handle the timer callback. This method is called when the timer fires - in this case, every 0.1 seconds.

- (void) updateStopWatchLabel
{
	nowTime = [NSDate timeIntervalSinceReferenceDate];
	NSTimeInterval interval = nowTime - startTime;
	
	int seconds = (int)interval;
	int tenths = (int)((interval - seconds) * 10);
	
	[timeLabel setText:[NSString stringWithFormat:@"%02d:%02d:%02d.%1d",(seconds/3600)%24,(seconds/60)%60, seconds%60, tenths]];
}

In the simulator and on the iPhone, the application looks like this:

Lessons learned

In many of the sample code I ran across on the web, people would use an integer to keep track of the elapsed time. Don't. NSTimeInterval is a quick way to grab the elapsed time in milliseconds from a fixed reference point. It's fast, neat, and works well. It would be easy to only have one function handle all the button UI. I kept it in two functions just to make it clearer, I hope. Enjoy.

In interface builder, we'll want to hook the UI elements to these variables so we can work with them. From Xcode's project window, open StopWatchViewController.xib. This will allow you to place the elements which will comprise the StopWatch application. Place a label and two buttons on the viewcontroller's window and initialize them with appropriate values. We'll tie the label and buttons to the variables timeLabel, startButton, and resetButton in StopWatchViewController by Control dragging from the File's Owner to each element. When you release the mouse, Interface Builder will prompt you for the appropriate variable. We'll also want to tie our two functions, startButtonPressed and resetButtonPressed to each of our buttons by Control dragging from the buttons to the StopWatchViewController. Be sure to save your work before switching back to Xcode.

With the buttons and label in place, let's go back to Xcode and modify the implementation file, StopWatchViewController.m, to put the whole thing together. First, we can add the two functions to handle each of the button presses:

- (IBAction)startButtonPressed:(id)sender
{
	if ([startButton.titleLabel.text isEqualToString:@"Start"]) 
	{
		// If the startButton is equal to start when it is pressed we want to 
		// disable the resetButton, change the text of the startButton to Pause, and
		// start keeping track of the time
		[resetButton setEnabled:false];
		[startButton setTitle:@"Stop" forState:UIControlStateNormal];
		
		startTime = [NSDate timeIntervalSinceReferenceDate];
		stopwatchTimer = [NSTimer scheduledTimerWithTimeInterval:0.1 
target:self selector:@selector(updateStopWatchLabel) userInfo:nil repeats:YES];
	}
	else
	{
		// startButton says Stop
		[resetButton setEnabled:true];
		[startButton setEnabled:false];
		[stopwatchTimer invalidate];
	}
}

- (IBAction)resetButtonPressed:(id)sender
{
	[timeLabel setText:@"00:00:00.0"];
	[startButton setTitle:@"Start" forState:UIControlStateNormal];
	[startButton setEnabled:true];
	[resetButton setEnabled:FALSE];	
}    

iPhone Stop Watch

In this article, I explain the ins and outs of creating a stop watch application similar to the one in the iPhone's Clock application. As a refresher, let's take a look at the start screen for the iPhone StopWatch. There's the Start and Reset buttons and a label indicating the time in tenths of seconds. This sample won't do anything too complicated like keeping laps.

Xcode Project

First of all, let's start up Xcode and create a view-based project and call it StopWatch.

Once the project has been created, Xcode will have the following project window.

Next, let's setup our variables. We know we need a label to hold the stopwatch's elapsed time. We will probably also need a couple of buttons. We'll also need some variables to figure out the elapsed time. So, open StopWatchViewController.h in xCode and add the following lines.

#import <UIKit/UIKit.h>

@interface StopWatchViewController : UIViewController {
	IBOutlet UILabel *timeLabel;
	IBOutlet UIButton *startButton;
	IBOutlet UIButton *resetButton;
	
	NSTimeInterval startTime;
	NSTimeInterval nowTime;
	NSTimer *stopwatchTimer;
}

@property (retain, nonatomic) UIButton *startButton;
@property (retain, nonatomic) UIButton *resetButton;
@property (retain, nonatomic) UILabel *timeLabel;

- (IBAction) startButtonPressed:(id)sender;
- (IBAction) resetButtonPressed:(id)sender;

@end

Hello World from the iPhone (part 2)

We continue our exploration of iPhone development. In part 1, we downloaded the latest version of Apple's development tools. In part 2, we'll create a simple iPhone application which displays the message "Hello World!".

Creating the Project

Let's start Xcode. We get the intro screen to xCode which looks like this:

Choose Create New Xcode Project:

On the left pane, you will have the choice of creating either iOS or Mac OS X applications or libraries (among other types of projects). Under the iOS selection, make sure the Application selection is chosen. For this project, we're going to choose a Window-based application. It will keep things very simple.

On the New Project screen, name the new project Hello World:

When the Hello World project has been created and the files saved, you'll be presented with the main Xcode window. In the left pane of the window, you'll see the Groups & Files which comprise the project. In the main pane of the window, you'll see a list of items which go into the building of the application. Take a minute and explore the items which comprise your project.

As a side note, I prefer the All-In-One view found under Xcode>Preferences. In later blog entries, I'll switch to this way of looking at things. Because I have a background using Visual Studio, I prefer one window to access project resources.

Building the Interface

Once we've created our project, we want to tell the World Hello! The development tools make this very easy to do. In the main project window, find the file named MainWindow.xib and double click on it. This will start the Interface Builder application. Interface Builder allows you to graphically design your application without having to wire up all the elements in your source code. For our Hello World project, Interface Builder would look like this:

Now select the Label item and move it to the window labeled Window. When you double click on the label item, you can change the text to "Hello World!". Let's do that and save the file and go back to Xcode.

Building the Project

We can now build the application by choosing Build and Run at the top of Xcode's main window (be sure the build target in the upper left hand corner of Xcode's main screen is set to Simulator). Xcode will automatically start up the iPhone simulator and launch your Hello World! application. Pretty easy:

Hello World from the iPhone (part 1)

For the majority of my professional career, I've developed software using Microsoft's platform and tools. Over the last year or so, I've started writing iPhone applications using Apple's tools running on a iMac. I thought I would share some of my experiences here on the blog.

Getting Ready/Getting Xcode

Before proceeding, you'll need to get a Mac - iPhone development can only be done on the Mac. There's no cross platform story here.

---

When I was at Microsoft in the late 90's, Java was perceived as the big threat because it allowed for cross-platform development. It's interesting to me that iPhone (and Mac) development is all about specifically targeting a single platform - the Apple platform. There doesn't seem to be much of a story for either Open Source or Cross Platform. This specific targeting of a single platform seems to have worked well for Apple.

---

So, you get the tools you need by going to Apple's development center. If you search for Xcode, it will take you to the download page. The download is free and requires you to join the Apple Development Program, which is also free (if you want to publish your iPhone application, you will have to pony up $99 to Apple to become part of their professional development program.)

In its current incarnation, Xcode reminds me a bit of where Visual Studio was back a couple of years ago. It is comprised of different applications which work together to build your code. These applications consist of:

• Xcode - Apple's IDE
• Interface Builder - application designer
• iPhone Simulator - for running iPhone applications on the desktop

XCode's IDE provides a wrapper around a powerful debugger - GDB. The IDE's wrapper buffers you from GDB's command interface which can be nice at times and can be frustrating at times.

---

Back in the Day - In some ways, the debugging environment reminds me a little of Windows development done in the early days when we used CodeView. Or if you use the general debugger under Windows now - windbg.

---

-(void)willAnimateSecondHalfOfRotationFromInterfaceOrientation:(UIInterfaceOrientation)<br/>
           fromInterfaceOrientation duration:(NSTimeInterval)duration
{
	UIInterfaceOrientation toOrientation = self.interfaceOrientation;
	
	[UIView beginAnimations:@"move buttons" context:nil];
	[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
	[UIView setAnimationDuration:2.0f];
	
	if (toOrientation == UIInterfaceOrientationPortrait || toOrientation == UIInterfaceOrientationPortraitUpsideDown) {
		// position elements
	}
	else {
		// position elements
	}
	
	[UIView commitAnimations];
}

• Tools - XCode and Interface Builder
• Foundation and UIKit
• Objective C (runtime?)

• Foundation
• Media
• Core Services
• Core OS

I just ordered a new IMac from B&H Photo (free shipping - oh, not quite $15 and tax - significant here in WA - about $200). The specs are:

• Quad-Core 2.66GHz Intel Core i5
• 8GB (4x2GB) RAM
• 1TB Hard Drive
• 8x SuperDrive DVD Burner, SD Card Slot
• ATI Radeon HD 4850 Graphics
• 27" LED Backlit 16:9 Widescreen Display
• iSight Camera, Bluetooth 2.1+EDR
• 802.11n Airport Extreme Wi-Fi
• Wireless Keyboard & Magic Mouse
• Mac OS X 10.6 Snow Leopard

Before I came to work at Microsoft, I worked at OCLC (technically, Ameritech bought our division right before I left). I did a variety of things at OCLC but one of the projects I got involved with was a pilot Macintosh project. In 1987, or so, OCLC became a developer partner with Apple. As a result they got an Apple Lisa (a firmware upgrade later, the MacXL) and one of the very early Macintosh's. When OCLC ended its pilot program, they gave me the Lisa/MacXL. I've kept it all these years and it is now out in the garage.

Well, after all these years I've decided to buy a Mac. I'll keep everyone posted on the experience!