We made another nifty little extension!

UIView+BlurFade is an Objective-C category lets you take any UIView and make it blurry and greyscale. This is super useful for when you want to make a view look disabled, and looks really pretty to boot!

This category uses Core Image to perform the blurring and grey-scaling. Because you can't apply CIFilters to views on iOS, it actually cheats a little bit - instead of gradually blurring the view over time, it blurs it once, stores it in an image, and then fades that image over your original content.

To use this category, just drop the two files into your project and #import them. Then, when you want to make your view go blurry and faded out, you just do this:

To remove the blur effect, you call its counterpart:

We hope you find UIView+BlurFade useful! If you have any comments, either create an issue on GitHub, or shoot us an email!

Once again PyCon Australia is being held in our hometown of Hobart, Tasmania, and one again we're sponsoring! We had an excellent time at PyCon Australia last year, and we're really looking forward to learning about the latest developments in Python, how to make games in Python, what not to do with Python, how to test with Python, security and Python, transitioning to Python, and much, much more! Congratulations to our friend and frequent collaborator, Chris Neugebauer (conference coordinator), for putting together such a a great show.

If you haven't registered for PyCon Australia yet, we strongly recommend you do! It's sure to be a blast.

You want to write an iOS or OS X app that quickly and easily retrieves some data from a server and converts it to an Objective-C class. Also, you want to write the server using something standard, like Django or Ruby on Rails.

The standard way that you’d do this would be using NSCoder, where your client application would receive the data and you’d unpack it like so:

However, the file format for serialised objects is internal to iOS and OS X, and is also a binary format that’s very difficult to read while in transit.

We recently had a similar problem, where we wanted to have our server send data in JSON format, which we like because JSON’s pretty human-readable. We could implement our own custom implementation of NSCoder, but we were after a more lightweight solution.

Key-value coding

This is where key-value coding comes in. Key-value coding is a feature of Cocoa that lets you access properties and instance variables of class at runtime by name, rather than simply at compile time.

For example, if you had a class that had an NSString property called “name”, you could access it like this:

Or you could access it with key-value coding, like this:

Likewise, you can set the name property like this:

But you could also set it using key-value coding, like this:

The advantage of key-value coding is that you can generate the keys at run-time. Your code doesn’t have to know about the properties and variables kept inside an object in order to attempt to get and set the values.

This is where our lightweight serialisation comes in. Let’s say that we’ve received some JSON data that looks like this:

In this example, we’ve also got an Objective-C object that has matching properties:

Converting the JSON data into a dictionary is pretty easy.

You can then create the Objective-C class from this dictionary by creating a new Employee object, and then iterating over each of the keys in the dictionary, using setValue:forKey: to set the values.

This works even for non-object properties like Employee’s income property, which is an int. In this case, the dictionary loaded from the JSON contains an NSNumber object for the income field; when setValue:forKey: is used for that key, it automatically extracts the int from the NSNumber and applies it to the class.

There’s an even easier way to set all of the values:

Loading objects when you don’t know the class

Another possible use case is one where you receive a chunk of JSON, but you don’t know ahead of time what kind of object the JSON should be turned into. This is where NSClassFromString comes in handy.

If your JSON object contains a field called, say, class, you can use that to create the empty object. Like so:

The reason we use NSObject in the above example is because all NSObjects support the key-value coding methods. Even though loadedObject is treated as a generic NSObject, the fact that it was created with whatever class ObjectClass is determined to be means that the object will be what you specify.

Dangers and Caveats

This technique only applies for simple properties, like strings and numbers. More complex data types or references to other Objective-C objects need to be handled differently.

If you use setValue:forKey: on a key that doesn’t exist in the target object, the object will throw an exception and crash. There are a couple of ways you can handle this; one is to implement the setValue:forUndefinedKey: method in your classes.

This method is called when you try to set a value for a property or instance variable that doesn’t exist. The default implementation throws an exception and crashes; you can implement your own that leaves a warning, for example.

A final note: this is a very quick-and-dirty solution. If you want more reliable behaviour, you’ll need to add more checks and validation code. For simply loading objects, it works pretty well.

While at OSCON this year, Jon and I were lucky enough to be interviewed by our editor, Rachel, for O'Reilly Radar. Find the interview embedded below, or check it out on O'Reilly. Our upcoming book, Learning Cocoa with Objective-C Third Edition, can be preordered now if you're interested! It's going to be amazing.

This was a fun one. As we've mentioned before, we're currently working on a board game for a client. Without going into the details, the game is based on nodes on a game board that are linked together; players move between connected nodes, and claim territory.

When coding up the game, we initially generated the game boards in memory, by directly instantiating 'node' and 'link' objects. Then, when it came time to make the game load different boards on demand, we created a JSON-based data structure that defines the nodes and links. It looks a little something like this:

This structure defines two nodes, including their names and positions, as well as a relationship that links the two together. (Because the graph is nondirectional, we didn't want to define links in the node data structure itself.)

This is all well and good for simple game boards, like this:

But then the client said, "cool, can you make this?"

And we were all:

Clearly, hand-coding wasn't an option, and a tool was needed. Writing one ourselves wouldn't have been the best use of our time, so we looked at our favourite Mac app ever: OmniGraffle Pro. OmniGraffle already knows about objects and connections, and it exposes all of this information through AppleScript.

So, we went searching, found this excellent Gist by Michael Bianco, and adapted it into one that extracts the information we need and generates the game board data that we care about.

Loosely put, it turns this:

Into a level that can be loaded:

How it works

First, we designed the level. In this board game, there are only nodes and connections; we represented nodes as circles, and connected the nodes with lines.

The first thing the script does, we get access to OmniGraffle via the Scripting Bridge:

OmniGraffle exposes a list of shapes, which AppleScript can query for important information such as the origin point, and its text. You can also query and set a special "tag" property for each shape, which is useful for storing an identifier. We base the identifier on the text of the shape, if it has any; otherwise, we use a random number.

So, to generate the list of game nodes, we ask OmniGraffle for all shapes, and format the result into a hash, which we store in an array for later.

When generating the hash for a node, we can also make use of the user data dictionary that OmniGraffle Pro exposes. This lets you set custom key-value pairs for a shape, which is very useful for setting things like which player owns a node, or at what point in the game the node becomes active. This is a simple matter of merging in the userData hash.

Once all nodes have been processed, we know that all shapes have had a tag associated with them; we can then iterate over all shapes a second time, this time generating information for each connection.

Finally, we export the nodes and links as JSON:

Because this script operates on the frontmost open document in OmniGraffle and outputs to stdout, saving the JSON is as simple as a one-line command: $ ruby graffle2board.rb > MyAwesomeBoard.board

Summary

This is a pretty powerful technique, since it lets us design the game maps with a powerful (and, more importantly, pre-existing) tool and import them exactly the way we want them. We're definitely going to be using this more in the future.

You can see the script in GitHub!

We recently needed to add a tutorial to a board game (see SLTutorialController), and realised that we needed a way to highlight various controls and other user interface elements that the user should interact with next. A common way that this is handled is by making things glow, often with an animation. So, we wrote UIView+Glow. It's a very simple category that adds two methods: startGlowing and stopGlowing. When you call startGlowing, the view will start to pulse with a soft light; this effect is removed when stopGlowing is called.

You can see a video of it in action here:

It's available on our GitHub now!