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In this post, I look at an approach for testing if an arbitrary pointer is a pointer to a valid Objective-C object. The result from the test is not absolutely accurate and can interfere with gdb debugging if the pointer isn't a valid memory location, so this is not something you'd want to do often (and certainly not in production code). But it can be a handy debugging tool for when you're staring blindly at memory you didn't allocate.
In this post, I build and run a Cocoa Mac application on the command-line. This might not sound like a very difficult goal but I'll attempt to follow an additional constraint: use as few tools, components, classes and even lines of code as possible; truly minimalist Cocoa programming. The goal is to create an application that qualifies as a proper Mac application (including a menubar and a window) but without using Xcode, without an Info.plist file, without NIB files, without Interface Builder and without even using a text editor other than the Terminal itself.
As pointed out by Mike Ash in his recent Friday Q&A 2009-11-13: Dangerous Cocoa Calls, NSHost is not thread-safe for use outside of the main thread and due to potentially slow, synchronous network access is not really suitable for use on the main thread either. Fortunately, in Cocoa there are often ways to transparently fix classes that don't work as they should. In this post, I'll show you how you can transparently patch NSHost using a drop-in solution and provide a non-blocking solution for NSHost lookups.
Objective-2.0 property methods are a nice convenience but if you need to override a property implementation — particularly an atomic, retained or copied object setter property — there are some potential bugs you can create if you don't follow the rules carefully. I'll show you the pitfalls and the correct way to implement a property accessor. I'll also show a way to directly invoke hidden runtime functions to let Objective-C perform atomic getting and setting safely for you.
You can configure your iPhone applications so that a touch in the status bar will scroll a UIScrollView to the top. I'll show you how you can intercept this touch event to use status bar touches for other purposes. The sample application will show a hidden drawer that slides out from the status bar when you tap it.
When Xcode is running, Interface Builder seems to magically know which classes, methods and variables are available. Where does Interface Builder get this information? How can you recreate this effect when editing source files in an external editor without Xcode running? This is the story of how I investigated the communication between Xcode and Interface Builder, so that I could recreate it for myself.
In this post, I'll show you how you can serve a Core Data document over a network using NSConnection. This arrangement will never be as efficient or safe as writing your own code to communicate the data over the network but the promise of transparent and automatic networking seemed too tempting to pass up.
The iPhone lacks specific methods to create UIEvent and UITouch objects. I'll show you how to add this functionality so you can write programmatically driven user-interfaces.
Ever wanted to override a method using a category but still invoke the default method from the category? Like invoking the super method on a super class, this example will show you how to invoke any "supersequent" method no matter if its on the super class, the current class or even another category on the current class.
I will show you how to use object forwarding to record any message in an NSInvocation, by simply sending the message to an object. Unlike techniques shown elsewhere, this will allow you to record any message, including NSObject messages and even the forwarding messages themselves.
For your debugging pleasure: a DebugBreak() macro to programmatically stop the debugger at a line of code (not inside a child function). Some of this code can be found elsewhere but I present it here, PPC and Intel capable and ready to run.
I wanted to get my new blog started with something that's unlikely to be found anywhere else. This is an obscure hack to access a fundamental piece of Objective-C data.
