Another Programming Blog

(mostly iOS and Ruby on Rails)

How to Keep Up With the Pace of Change

Seth Godin recently published a short post called “The full stack keeps getting taller”, in which he basically advices us to leave a particular field of interest as soon as it’s taken for granted - when it becomes part of the lower stack. A commodity, perhaps.

However, while top of the stack changes quickly, the bottom of the stack changes slowly.

It’s the principle of inertia. If you have two soccerballs, and one is filled with lead instead of air, then you’d need to apply more work to accelerate it to the same speed as the other.

What I mean is this: There’s much more built on top of TCP/IP than there is, for instance, on top of Gulp.js.

And if it’s easier to go from the basics to a specialization than vice versa [1], it pays to have a solid foundation, and a good grasp of core technologies.

This way, jumping from technology to technology should require much less effort.


[1] I think this is the case, especially if we have not neglected to learn new things in the past. If we ever only cared about Java programming, and never bothered to look at Assembler or Clojure, we might end up a one trick pony. But if there’s a little experience in different fields under our belt, we get very good at adapting.

macThesaurus: A Mac-app Written With Node-webkit

I decided to play around with node.js, specifically with node-webkit.

Node-webkit allows programmers to write desktop-apps with Javascript, and even package them for distribution, for example via the Mac App Store. (Check out this list of apps written with it.)

To play with it, I’ve decided to write a tiny thesaurus-app.

  • It should lookup and display synonyms and related words using a (German) thesaurus via the JSON-API at
  • To be really useful, it should be possible to bring the app to the foreground using a keyboard shortcut. In my case it’s Shift+Alt+T.
  • It should be possible to dismiss the app by tapping ESC

It worked quite nicely. The app doesn’t really feel like a web-app, even though it utilizes web-app technologies. And I could even create a binary for the App Store.

Here’s a short video of the app in action:

And here’s the source on Github.

Monty Hall Simulation

Here’s a simulation of the Monty Hall Problem.

# this is about

num_rounds = 5000
num_correct_guesses_keep = 0
num_correct_guesses_switch = 0

num_rounds.times do

        doors = [false, false, false]
        doors[rand(3)] = true

        # first pick = random

        player_pick = rand(3)
        show_bad_door = doors.index(true)

        # show a bad door that is not the price_door and not player's pick

        while (doors[show_bad_door] || show_bad_door == player_pick)
                show_bad_door = rand(3)

        # second pick, player choses to switch to the other door
        remaining_doors = [0, 1, 2]

        player_switch_pick = remaining_doors.first        

        win = if doors[player_pick]
                num_correct_guesses_keep += 1

        win_switch = if doors[player_switch_pick]
                num_correct_guesses_switch += 1

        puts "doors: #{doors}, show_bad_door: #{show_bad_door}, "\
        "player keeps: #{player_pick}, player wins: #{win}, "\
        "player wins if he switches: #{win_switch}"


win_ratio = ( num_correct_guesses_keep.to_f / num_rounds.to_f * 100.to_f ).round(2)
win_ratio_pick = ( num_correct_guesses_switch.to_f / num_rounds.to_f * 100.to_f ).round(2)
puts "correct: #{num_correct_guesses_keep}, correct-switch: #{num_correct_guesses_switch}, "\
         "win-ratio: #{win_ratio}%, win-ratio switch: #{win_ratio_pick}%"

Switching really doubles the probability to win. Dang it. ;)

Reminder to Self: Code-Folding in XCode (With Keyboard Shortcuts)

Just a reminder for myself. How to fold and unfold code in XCode:

  • ⌘ + ⌥ + ⇧ + ← fold all methods in file.
  • ⌘ + ⌥ + ⇧ + → unfold all methods in file.
  • ⌘ + ⌥ + ← fold block underneath the cursor.
  • ⌘ + ⌥ + → unfold block underneath the cursor.

New App: Zones

I’ve just uploaded my new app. It is called “Zones” and it’s one of those desktop helper tools for Mac OS X. You can take a look at Zones here.

It was fun to do and I learned a bunch of stuff about Mac OS X. It was probably also the last side-project ever written in Objective-C for me, since the Apple world is switching to Swift now. (Which is good.)

Sadly, I cannot distribute the app through the AppStore, because it cannot be sandboxed using the APIs it does (Accessibility). Which means I will probably never earn enough money to buy a happy meal with it.

How to Revert iOS8 Beta 1 Back to iOS 7.1.1

I needed to go back to iOS 7 after a few apps, most notably Whatsapp, no longer worked properly. I also had no restore points for some reason.

Here’s a way to turn your iOS 8 iPhone back into an iOS 7 iPhone:

  1. Attach phone to Mac
  2. Start iTunes
  3. Hold Power and Home Button on the phone. When it restarts let go of the power button and only keep the Home button pressed.
  4. iTunes will say it detected a phone in recovery-mode
  5. Proceed with the recovery instructions.

You don’t need to donwload any images before hand, iTunes will do it for you.

In my case I ended up with a completely blank iPhone. But I could restore Contacts, some settings etc. from iCloud.

iOS: Restrict Panning of UIPageViewController to a Certain Area

Another iOS code-snippet:

I had a UIPageViewController in scrolling-mode that would allow to pan between view-controllers using a finger gesture. However, I wanted to restrict the panning area to a certain area of the screen, for example as shown in this screenshot:

Restricted Panning Area UIPageViewController

I do it by subclassing the UIPageViewController, finding its UIScrollView, and adding a new UIPanGestureRecognizer to that scrollView.

I set my subclassed UIPageViewController to be the delegate of that new UIPanGestureRegognizer. I then implement two delegate methods:

#import "LZPageViewController.h"

@interface LZPageViewController ()


@implementation LZPageViewController
  UIPanGestureRecognizer *_scrollViewPanGestureRecognzier;

- (void)viewDidLoad
  [super viewDidLoad];
  // Do any additional setup after loading the view.
  for (UIView *view in self.view.subviews) {
    if ([view isKindOfClass:[UIScrollView class]])
      UIScrollView *scrollView = (UIScrollView *)view;
      _scrollViewPanGestureRecognzier = [[UIPanGestureRecognizer alloc] init];
      _scrollViewPanGestureRecognzier.delegate = self;
      [scrollView addGestureRecognizer:_scrollViewPanGestureRecognzier];

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer
shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer
  return NO;

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
  if (gestureRecognizer == _scrollViewPanGestureRecognzier)
    CGPoint locationInView = [gestureRecognizer locationInView:self.view];
    if (locationInView.y > SOME_VALUE)
      return YES;
    return NO;
  return NO;

In the last override I decide if I want to “eat the event” (reply YES) or if I want the original UIPanGestureViewRecognizer of the UIScrollView to handle it (reply NO). So, the YES-reply means the UIPageViewController will not scroll to the next ViewController.

iOS: How to Resize and Rotate an UIImage - Thread Safe Version

Here are two code snippets for rotating and resizing UIImage’s without using UIGraphicsBeginImageContext(), because it is not thread-safe and can lead to weird behavior.

In my case the camera-preview when taking a picture in an app I was writing, turned black from time to time. The problem was that I was rotating and resizing the images using UIGraphicsBeginImageContext().

Here’s some code I’ve found and tweaked to resize images:

- (UIImage *)imageByScalingToSize:(CGSize)targetSize
  UIImage *newImage = nil;
  CGFloat targetWidth = targetSize.width;
  CGFloat targetHeight = targetSize.height;

  CGContextRef bitmap = CGBitmapContextCreate(NULL,
                                              4 * targetWidth, CGImageGetColorSpace(self.CGImage),
  CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth, targetHeight), self.CGImage);
  CGImageRef ref = CGBitmapContextCreateImage(bitmap);
  newImage = [UIImage imageWithCGImage:ref];
  if(newImage == nil) NSLog(@"could not scale image");
  return newImage ;

And here’s how to rotate them:

- (UIImage*)rotateInRadians:(CGFloat)radians
        CGImageRef cgImage = self.CGImage;
        const CGFloat originalWidth = CGImageGetWidth(cgImage);
        const CGFloat originalHeight = CGImageGetHeight(cgImage);

        const CGRect imgRect = (CGRect){.origin.x = 0.0f, .origin.y = 0.0f, 
                .size.width = originalWidth, .size.height = originalHeight};
        const CGRect rotatedRect = CGRectApplyAffineTransform(imgRect, CGAffineTransformMakeRotation(radians));

        CGContextRef bmContext = NYXImageCreateARGBBitmapContext(rotatedRect.size.width, rotatedRect.size.height, 0);
        if (!bmContext)
                return nil;

        CGContextSetShouldAntialias(bmContext, true);
        CGContextSetAllowsAntialiasing(bmContext, true);
        CGContextSetInterpolationQuality(bmContext, kCGInterpolationHigh);

        CGContextTranslateCTM(bmContext, +(rotatedRect.size.width * 0.5f), +(rotatedRect.size.height * 0.5f));
        CGContextRotateCTM(bmContext, radians);

        CGContextDrawImage(bmContext, (CGRect){.origin.x = -originalWidth * 0.5f,  .origin.y = -originalHeight * 0.5f, 
                .size.width = originalWidth, .size.height = originalHeight}, cgImage);

        CGImageRef rotatedImageRef = CGBitmapContextCreateImage(bmContext);
        UIImage* rotated = [UIImage imageWithCGImage:rotatedImageRef];


        return rotated;

Because the above takes radians, convert using something like this:

CGFloat DegreesToRadians(CGFloat degrees) {return degrees * M_PI / 180;};

Just put these methods into a category on UIImage.

iPhone/iOS Tutorial: How to Write an Image-cropper

This kept me busy for a while until I found a super simple way to do it: In this tutorial/code-snippet I’ll show you how to write an image-cropper for your iPhone-app.

What do I mean by image-cropper?

Bascially, it’s about giving your users a simple way to select part of an image using pan and pinch gestures. This can be handy when they upload a profile picture or something similar.

Here’s the end result:

How it’s done:

There is one UIScrollView with a large contentSize. Embedded in the scroll-view is a UIView (baseView). And embedded in the baseView is the UIImageView with the Ferrari-picture.

LZCropperExample sketch

The yellow boxes in the above image represent the iPhone screen and the cropping area.

Because the contentSize is bigger than the bounds of the screen (= frame of _scrollView), the user can pan to select the desired image. Because minimumZoomScale and maximumZoomScale are set, the user can pinch to zoom. (Although I am not sure why it helps to set the initial zoomScale after all other initialization. If it’s done earlier it won’t scroll until zoomed.)

The actual cropping is done by rendering the contents of the view-controller’s view into an ImageContext and then cutting out the portion that (here: roughly) corresponds to the non-dimmed “window” in the center.

The image is then saved to the phone’s photo gallery.

Get the example project from Github and take a look at the code. It’s actually very simple and self-explanatory.

Here’s the actual cropping code that is executed when you tap the “OK”-button.

- (void)pickResult:(id)sender // ehm.. not sure why I needed sender here.. ;)
  // some visual feedback a.k.a. special effects:
  _acceptButton.enabled = NO;
  _specialEffectsView.alpha = 1.0f;
  [UIView animateWithDuration:1.0f animations:^{
    _specialEffectsView.alpha = 0;
  } completion:^(BOOL finished) {
    _infoLabel.alpha = 1.0f;
    [UIView animateWithDuration:1.0f animations:^{
      _infoLabel.alpha = 0;
      _acceptButton.enabled = YES;

  // 1. hide stencil overlay
  _stencilView.hidden = YES;
  // 2. take a screenshot of the whole screen
  [self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
  UIImage *screenshot = UIGraphicsGetImageFromCurrentImageContext();
  // 3. pick interesting area and crop
  CGImageRef imageRef = CGImageCreateWithImageInRect([screenshot CGImage],
                                                     CGRectMake(35.0f, 159.0f, 248.0f, 248.0f));
  UIImage *croppedImage = [UIImage imageWithCGImage:imageRef];
  // 4. just for fun, resize image by factor 2
  UIImage *resizedImage = [croppedImage resizedImageToSize:
                           CGSizeMake(croppedImage.size.width * 2, croppedImage.size.height * 2)];

  // 5. save result to photo gallery
  UIImageWriteToSavedPhotosAlbum(resizedImage, NULL, NULL, NULL);
  // 6. show stencil view again
  _stencilView.hidden = NO;

Very straightforward stuff.

But as I said, it took me a while. For some reason I never thought of taking a screenshot first.. ;)

Also this solution has the limitation of pixel size. If you want to crop an image of for example 10000 times 10000 pixels and get half of it, you would expect a 5000x5000 pixel result. However, because of the screenshot technique, the cropped area will never be bigger than the pixels on the iPhone screen.

Emailserver Page Is Offline

I’ve scrapped the website where I offer setting up your email-server. While it was fun to learn and experiment with, and while some have expressed interest in the offer, it’s neither pracitcal nor profitable for me to continue offering it.

Please refer to this post for information how to start with the email topic yourself. It describes a simple way of setting up an emailserver with Ubuntu.