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Category Archive for ‘Recipes’ rss

What to Do When Xcode Beachballs

Apple keeps working on making Xcode more stable all the time. While Xcode 4.6 has much improved in terms of simply quitting on you, people report that more often now they see Xcode just hang.

One method to deal with race conditions in a highly parallelized application like Xcode is to add semaphores and locking. Unfortunately locking is not the end-all of all all Xcode problems, even with a liberal sprinkling. A blocked main thread is a blocked main thread.

Spinning Beach Ball

Here is what you should do next time you encounter the beach ball of doom.

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UIView Background Queue Debugging

Over the the past few days we’ve been chasing an elusive bug that was testing the limits of our sanity. We repeated the following conversation about 3 times:

“Hey, we did some changes. The jumping views should not occur any more. We didn’t see it even after 2 hours of testing”
“I’m still getting it, right after launching the app.”
“&”ยง%, $%&% &!”

I would bet that this happened to you to, especially when working with background queues for updating some data and then updating UI to reflect the new information.

Similar to “did you reboot your PC?” being the standard answer to 99% of Windows problems, we iOS developers found that “are you maybe calling UIView methods on a background thread?” solves the Lion-share of problems with views. Here’s a convenient way how you can quickly find these elusive issues too.

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Xcode 4.6 Libtool Issues

The updated linker and libtool that come with Xcode 4.6 apparently contain some changes that are causing problem when building projects that link and depend on static libraries. One appears to be a bug, the other is an annoyance. Fortunately we found workarounds for both.

Update: Not a bug after all. Rather a “learning experience”. Details below.

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3 Mac Tidbits

Here are three small pieces that I discovered while working on my second major Mac app. It’s for internal use by a client, so I cannot tell you about it, but it is a great place for me to learn more about the various oddities you find when developing for the Mac platform.

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Unit-Testing CoreData Migrations

If you use CoreData then you will probably face the problem of database migration sooner or later. Automatic migration is turned on easily, but how can you be reasonably sure that your fresh app update will still be able to open databases using the old schema? Like when people were using the app and are now installing your update that needs more entities.

We were beginning to face this scenario in multiple apps, so we started unit testing CoreData automatic migrations like I’m going to show in this article.

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OMG, GCD+ARC

There are a few trailblazing developers out there who intentionally set their app’s deployment target to iOS 6. When dealing with open source libraries like DTCoreText this might give you a fair share of deprecation warnings. But there is also another problem caused by this that library vendors need to address.

The SDK used should always be the Latest iOS, but the Deployment Target setting tells the compiler and linker at what level of fanciness it can enable the turbo features.

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Digging into CocoaPods

There once was a developer who figured that it would make sense to not reinvent the wheel, or at least not all 4 that he needed for his app/car. He had previously learned how to contribute to open source projects on github and wrapped his head around git submodules. As long as you stay in the git ecosystem all is bliss, submodules contain Xcode projects which are easily added as sub-projects.

The big advantage of sub-projects is that you can debug into these and if you fix something you can easily push that back to the master repository. But this convenience brings with it a drawback: since you have to keep a copy of each sub-module in each project structure that needs them you risk ending up with many different versions of many different components all over your file system.

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Open In … All Files

Let’s say you are building an app that does some sort of file handling where you want to be able to open any and all file types in your app. When your app then launches it would do something with the file, like upload it to a server.

I was not quite certain how to achieve this effect myself, so I turned to Dropbox who are doing exactly that. If you have the Dropbox iOS app install you can open any file in Dropbox. Then you can choose where to put it in your online storage.

How did they do that? Did they register for a truckload of file types? Or is there a shortcut that I didn’t know about yet?

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Changing History … Git’s

I had my PDF experiments inside DTFoundation. Those included a rather large (compared to the other source code) PDF file I was using for testing and the Demo. The problem with this was that I’m using DTFoundation almost everywhere now, being the central repository for all my generally reusable code.

Because of this file every cloning of the repository would take forever. So I decided to split the PDF stuff into its own repository and I deleted the file. However – since git keeps all history forever – the clones would still take long.

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First Good Auto-Layout Use-Case

While developing away on my iCatalog Editor I found what I believe to be the first instance in my career as developer where Auto-Layout actually saves me a lot of work.

Before Auto-Layout you would have to calculate view frames and apply them, usually in a layoutSubviews on iOS. The problem being that it usually takes lots of experimentation to get all the cases right.

In my use case I wanted to create a panel for my Mac app that would dynamically adjust to an optional icon on the left side and an optional cancel button on the right, with a progress bar in between. Auto-Layout (after some initial non-understanding on my part) made this a sinch.

While I am exploring constraints for a Mac app, the exact same methods also apply for iOS development.

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