Custom Draw

I'm gonna post some boilerplates so I don't have to look it up again.

UIKit's way to draw is to use Quartz.

Basic drawing requires 3 steps:

  • overload the drawRect method of the UIView class
  • wrap the custom view in a view controller
  • add this controlled view in a container, e.g. the window.

1. overload drawRect

Create a custom UIView class

ScoreView.h

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#import <UIKit/UIKit.h>

@interface ScoreView : UIView {
}

@end

ScoreView.m

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#import "ScoreView.h"

@implementation ScoreView

- (void)drawRect:(CGRect)rect {
   // Drawing code
  CGContextRef _context = UIGraphicsGetCurrentContext();
  CGRect _rect = CGRectMake(40, 40, 240, 120);

  CGContextSetRGBFillColor(_context, 0.0, 0.0, 1.0, 1.0);
  CGContextFillRect(_context, _rect);
}

@end

2. wrap in a controller

KonViewController.h

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#import <UIKit/UIKit.h>

@class ScoreView;

@interface KonViewController : UIViewController {
  ScoreView *scoreView;
}

@property (nonatomic, assign) ScoreView *scoreView;

@end

KonViewController.m

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#import "KonViewController.h"
#import "ScoreView.h"

@implementation KonViewController

@synthesize scoreView;

- (void)loadView {
  self.wantsFullScreenLayout = YES;

  ScoreView *view = [[ScoreView alloc] 
                     initWithFrame:[UIScreen mainScreen].applicationFrame];
  self.view = view;
  self.scoreView = view;

  [view release];
}

@end

3. attach to window

KonAppDelegate.h

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#import <UIKit/UIKit.h>

@class KonViewController;

@interface KonAppDelegate : NSObject <UIApplicationDelegate> {
  UIWindow *window;
  KonViewController *konViewController;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) KonViewController *konViewController;

@end

KonAppDelegate.m

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#import "KonAppDelegate.h"
#import "KonViewController.h"

@implementation KonAppDelegate

@synthesize window;
@synthesize konViewController;

- (void)applicationDidFinishLaunching:(UIApplication *)application {    
  self.konViewController = [[[KonViewController alloc] init] autorelease];

  [window addSubview:konViewController.view];
  [window makeKeyAndVisible];
}


- (void)dealloc {
  [konViewController release];
  [window release];
  [super dealloc];
}

@end

Those are the only 6 files I needed to make the app compile, besides the never changing main.m.

I did find some problem with UIKit though, in particular, errors could pass on silently. I had to guess very hard what the problem could be. Anyway, need to find a better debugging method.

Compile

After following the excellent documentation by Stephen Blackheath, I was able to setup a new project with GHC support in no time.

The simplest iPhone program that compiles looks like this

main.m

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#import <UIKit/UIKit.h>

extern int Haskell_main(int argc, char* argv[]);

int main(int argc, char *argv[]) {
  Haskell_main(argc, argv);
}

int kon(void) {
  NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
  int retVal = UIApplicationMain(0, nil, nil, nil);
  [pool release];
  return retVal;
}

Main.hs

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{-# LANGUAGE ForeignFunctionInterface #-}

import Foreign.C.Types

foreign import ccall safe "kon" kon :: IO CInt

main = kon

main.m calls into haskell's Main.hs, and haskell calls back via FFI a function that init the UiKit.