Excellent discussion on MonoTouch vs XCode/Objective C

I came across this recently and given that you get both sides of the story (well at least almost) its not a bad way of considering the two big options for iPhone development.



CannonAttack iPhone v1.0 – An iPhoneTutorial

Which way to the battle? –  The Introduction

This tutorial is a short introduction to iPhone development. Like most of my tutorials it’s based on a game.

This is the second in a series of tutorials. The first tutorial was a TDD tutorial in C# 4.0.

This version of the tutorial is similar in functionality to the C# version with obvious changes to the UI as needed. I am not using a TDD approach, mainly because I am not really up to TDD on the iPhone yet.

By completing this tutorial you will:

  • Get a taste of the iPhone development experience; and
  • Design a simple UI in Interface Builder.

CannonAttack iPhone is a simple game where a player enters an angle and velocity of a cannonball to hit a target at a given distance. The game uses a basic formula for calculating the trajectory of the cannonball and the player keeps taking turns at shooting at the target until it has been hit

Where are the cannonballs – What you need:

I built this with the following tools:

  • iPhone SDK (3.1); and
  • MAC OS X 10.6 Snow Leopard

Whilst this is a pretty basic introduction to iPhone development, it assumes a very basic knowledge of iPhone development and while it doesn’t spell out every single step, you should have more than enough detail to complete it.

The battleplan – The CannonAttack Requirements/Specs:

The following is a combination of Requirements and Specifications that will give us some guide in terms of the application we are trying to build:

  • iPhone Application;
  • Allow player to set Angle and Speed of the Cannon Ball to Shoot at  a Target;
  • Target Distance is simply the distance of the Cannon to Target, and is created randomly by default but can be overridden;
  • Max distance for target is 20000 meters;
  • Base the algorithm for the calculation of the cannons trajectory upon the following code (distance and height is meters and velocity is meters per second):

distance = velocity * Math.Cos(angleInRadians) * time;

height = (velocity * Math.Sin(angleInRadians) * time) – (GRAVITY * Math.Pow(time, 2)) / 2;

  • A hit occurs if the cannon is within 50m of the target;
  • Display number of shots for a hit

Building the Cannon – Creating the Cannon UI

  • Start XCode and Create a View based application – call it CannonAttack
  • Now add a class to the Project and call it Cannon.m (generate the .h file as well).
  • Double click on the file CannonAttackViewController.xib:  (this will open up Interface Builder).
  • Create the following UI using the design tools in IB (base this on this screen):

  • Also, Add a button that covers the whole screen in the iPhone UI in Interface Builder. Click on this button and from the LAYOUT Menu select SEND TO BACK. This is important as we will use this hidden button to remove the keyboard for the textfields when we click in the background or one of the buttons.
  • Also make sure you have set the keyboard type for the textboxes to number pad.
  • You need to then go back to XCode and add the following Code to the .h file.
  • Now add the following to the .m file

#import <UIKit/UIKit.h>
@interface CannonLauncher1ViewController : UIViewController {
IBOutlet UILabel *descriptionLabel;
IBOutlet UILabel *resultLabel;
IBOutlet UITextField *speedTextField;
IBOutlet UITextField *angleTextField;
IBOutlet UILabel *shotCountLabel;
int targetDistance;
int shotCount;
@property (nonatomic,retain) UILabel *descriptionLabel;
@property (nonatomic,retain) UILabel *resultLabel;
@property (nonatomic,retain) UITextField *speedTextField;
@property (nonatomic,retain) UITextField *angleTextField;
@property (nonatomic,retain) UILabel *shotCountLabel;

So now add the following code to the .m file

#import "CannonLauncher1ViewController.h"
#import "Cannon.h"
@implementation CannonLauncher1ViewController
@synthesize descriptionLabel;
@synthesize resultLabel;
@synthesize speedTextField;
@synthesize angleTextField;
@synthesize shotCountLabel;
- (void)viewDidLoad {
[super viewDidLoad];
[self resetTextBoxes];
//Button handler for the fire button
-(IBAction) fireButton:(id) sender
NSInteger velocity = [[speedTextField text]intValue];
NSInteger angle = [[angleTextField text]intValue];
Cannon *cannon = [[Cannon alloc]init];
cannon.targetDistance = targetDistance;
[cannon Shoot:angle Speed:velocity];
shotCount ++;
resultLabel.text = cannon.message;
shotCountLabel.text =
[NSString stringWithFormat: @"Shot Count %d", shotCount];
[self hideNumberKeyboard];
[cannon release];
//Button handler for the reset button
-(IBAction) resetButton:(id) sender
[self resetTextBoxes];
//Button Handler for the main backgtound button
[self hideNumberKeyboard];
//Hides the number keyboard
[speedTextField resignFirstResponder];
[angleTextField resignFirstResponder];
//Reset the distance and set it as rge text of the description label
targetDistance = rand() %10000;
NSString *distanceText = [[NSString alloc] initWithFormat: @"Distance %d meters (50m",targetDistance];
descriptionLabel.text = distanceText;
speedTextField.text = @"";
angleTextField.text = @"";
shotCount = 0;
[distanceText release];
//Built in Method I didn't change this
- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];
//Built in Method to clean up any objects
- (void)dealloc {
[descriptionLabel release];
[resultLabel release];
[speedTextField release];
[angleTextField release];
[shotCountLabel  release];
[super dealloc];

OK so all we have to do now is implement the cannon class.

Now edit the cannon.h file and replace the code with this header code:

//  Cannon.h
//  CannonLauncher1
//  Created by Dom Millar on 16/06/10.
//  Copyright 2010 __MyCompanyName__. All rights reserved.
#import <Foundation/Foundation.h>
@interface Cannon : NSObject {
@private int targetDistance;
NSString *message;
@property  (readwrite,assign)int targetDistance;
@property  (nonatomic,retain) NSString *message
-(IBAction) Shoot: (int) angle Speed: (int) speed;

Now all we have to do is add the code for cannon.m

//  Cannon.m
//  CannonLauncher1
//  Created by Dom Millar on 16/06/10.
//  Copyright 2010 __MyCompanyName__. All rights reserved.
#import "Cannon.h"
@implementation Cannon
@synthesize targetDistance;
@synthesize message;
-(IBAction) Shoot: (NSInteger) angle Speed: (NSInteger) velocity
//set up the local variables for the shoot method
float time = 0;
float height = 0;
float distance = 0;
float gravity = 9.80665;
float variation = 50;
float pi = 3.1415926536;
//Keep calculating height and distance untill height < 0
while(height >= 0)
float angleInRadians = ( pi / 180 ) * angle;
distance = velocity * cos(angleInRadians) * time;
height = (velocity * sin(angleInRadians)) - (gravity * pow(time,2));
//Complete calculation
if ((targetDistance >= distance-variation) && (targetDistance <= distance+variation))
//Display the hit
message = @"Hit";
//Display the Miss
NSString *description = [NSString stringWithFormat:@"Missed target landed at %f meters" , distance];
message = description;
//[description release];

Now make sure everything builds. Go back interface builder and you need to do setup the following outlets and actions:

This shows you all the hooks we need:

File owner dialog screen shot

OK now You should be ready to run, go back to XCode and run the app and you should be able to play the game like:

You can see the Keyboard is visible here – once we click on a button or the main screen the keyboard will disappear:

Victory Condition – In summary

So that’s it – our latest version of the Cannon Attack game is complete. There are lots of changes you can make to make the game more interesting so play around with the project as much as you like.

Happy Coding – Dom.

Fixing the Expired Certificate for iPhone Development Environment


This is a short guide to resolving the issue of the expired certificate using XCode with the iPhone SDK – its probably relevant for setting up your certificate from scratch as well. I am not totally convinced this is the best way of fixing the expired certificates for iPhone Development, but it worked for me so.

The Environment:

The development environment  is a follows:

  2. SnowLeopard OS;
  3. XCode 3.2 ; and
  4. iPhone developer program member.

The Problem:

You’ll may get a variety of messages when the certificate expires and they will include:

a valid signing identity matching this profile could not be found in your keychain

or :


code sign error: the identiy matching this profile could not be found in your keychain



You currently do not have a valid certificate

Getting a new certificate:

  1. From Applications->Utilities Click KeyChain Access
  2. From the Keychain Menu Select Certificate Assistant->Request a Certificate From a Certificate Authority
  3. Enter your email address and your common name and select Save to disk
  4. Go to http://developer.apple.com/iphone/index.action and login
  5. Go to the Provisioning portal in the iphone developer and select Certificates
  6. Remove the existing certificate
  7. Add a new certificate
  8. Choose File selects the file you created in step 3
  9. Click Approve
  10. Reload the page. Now you should see the download button.
  11. Click Download
  12. Then select it the downloaded file
  13. You will receive a dilog stating “Do you want to add the certificates from the file…. To a keychain”. Select YES.
  14. Click Add and you should see the certificate list with the new valid certificate displayed.
  15. That’s all you should have to do however you may notice a dialog asking you to use the new key – just select Allow or Always Allow.


Combining .Net and iPhone Development (Part 2 Adding another string to the bow)

Often when you read blogs or articles on improving .NET development skills you’ll find a recurring theme : learn another language or learn a new technology. For the C# .Net developers that usually means looking at languages like VB, Ruby, Java, PHP, Pytho. In terms of technologies it involves looking at one of the myriad of .Net technologies like MVC, Silverlight, Entity Framework, WPF, AJAX, jQuery,Windows Mobile etc… etc…

So the main reason this is a recurring theme, is because as a developer by learning new language you are taking yourself outside your comfort zone and exposing yourself to a new syntax, techniques, tools and frameworks. Whilst this can be daunting at times or may even seem slightly pointless (ie. If you are a great VB.NET developer in a great  VB.NET job why would waste your time changing), you need to consider the potential benefits in applying yourself to a new language.

Now iPhone development is not the most logical move for .Net developers. Historically, there is a fair bit of tension and antagonism between the Apple and the Microsoft camps. Suggesting there is a logical reason to  combine the development skillsets of the two big competitors may not seem that sensible. However, from a .Net developers perspective I feel there is a significant case to add the iPhone SDK to your skillset including:

  • The massive growth in iPhone usage is now starting to see a change in job prospects for iPhone developers. For Australian developers just type “iPhone” in a developer job role in www.seekit.com.au and notice the number of roles appearing for the iPhone.
  • Adding another language to your toolkit makes you more flexible – a downturn in one specific toolset market may not impact another market as seriously.
  • Having iPhone SDK experience or projects on your CV is significant (the above two reasons are pretty good reasons for this).
  • iPhone usage is massive – if you sersiously think you want to develop and publish apps, the appstore provides you the perfect avenue
  • The syntax whilst different is not that hard to learn particularly with some good references.
  • Additional devices (including iPad) are based on the same fundamental development environment.

Next Part 3 – Ok I want to do some iPhone Development what do I need?