Last night’s CocoaHeads was a blast. Alondo, you have to come give an intermediate/advanced talk on Storyboards. Thanks a lot to @scottpenrose for his lightning and thunder, and @flightblog for his inspiration (METAR gave me a lot of headaches, too). And of course, thanks especially to Josh for organizing everything. And a new place for NSCoder? You rock.
For those who didn’t scribble notes fast enough, my Core Foundation presentation is attached (including the fix for my memory leak; was it Jay who found that?) I’ll make sure to fix the code in the book for the next edition.
Building a Core Foundation.pdf
When last we looked at Bézier curve calculations, we were able to calculate five million points in about 0.6s (~8.3Mp/s or megapoints-per-second). That’s 1000 points per curve, 100 curves, at 50fps. That was 5x faster than the original -Os optimized function. But we’re just getting warmed up. We haven’t yet gotten half of the performance available.
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[If you want the answer to last time's homework, skip to the end.]
So you want to hand-calculate Bézier curves. Good for you. It comes up more often then you’d think on iOS, even though UIBezierPath is supposed to do it all for you. The truth is, sometimes you need the numbers yourself. For instance if you want to calculate intersections, or you want to draw text along the curve (like in CurvyText from iOS:PTL chapter 18).
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The most up-to-date source for this is now available at github.
Your programs need to deal gracefully with being offline. Mugunth Kumar has built an excellent toolkit that manages REST connections while offline called MKNetworkKit, and Chapter 17 of our book is devoted to the ins-and-outs of this subject.
But sometimes you just have a simple UIWebView, and you want to cache the last version of the page. You’d think that NSURLCache would handle this for you, but it’s much more complicated than that. NSURLCache doesn’t cache everything you’d think it would. Sometimes this is because of Apple’s decisions in order to save space. Just as often, however, it’s because the HTTP caching rules explicitly prevent caching a particular resource.
What I wanted was a simple mechanism for the following case:
- You have a UIWebView that points to a website with embedded images
- When you’re online, you want the normal caching algorithms (nothing fancy)
- When you’re offline, you want to show the last version of the page
My test case was simple: a webview that loads cnn.com (a nice complicated webpage with lots of images). Run it once. Quit. Turn off the network. Run it again. CNN should display.
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For those who have asked, the Adobe E-Book version of iOS 5 Programming is available now from Wiley. I’m not certain yet when the Kindle version will be out, but I’m looking into it, along with getting a list of what other formats are planned.
I have no idea what Amazon rankings really mean right around a book launch. Since they weight towards recent sales, I’m sure they spike, so you have to take these things with a grain of salt. But for at least a little while, we have the #1 book in Mobile & Wireless Programming. I promise I won’t keep spamming you all with book updates, but it’s the first time I’ve been at the top of a “best sellers” list.
Amazon's product details 2011-12-14
I’ve mentioned that Mugunth Kumar and I have been working on a book, iOS 5 Programming Pushing the Limits. It’s available now for pre-order and should be shipping by 12/20. It will be available in several eBook formats, though I don’t have all the details for that yet. I’m proud of what we’ve been able to put together here. The target audience are developers who have some iOS development under their belts, and are ready to move to the next level. Rather than just focus on the nuts and bolts of getting things done, we cover how to do things well. In the process, we cover a lot of more advanced ground, often of frameworks with “Core” in their names like Core Animation, Core Text, and Core Foundation. We also address practical issues like how to optimize your application for offline work, and how to best handle REST and JSON.
Please send any comments or corrections to me at robnapier@gmail.com. In the meantime, you can take a look at the example code.
Update: You can now download the full example code from my book at GitHub. This comes from Chapter 11, “Batten the Hatches with Security Services.”
Update2: The things described here are handled automatically by RNCryptor, which is an easier approach unless you want to write your own solution.
I see a lot of example code out there showing how to use CCCrypt(), and most of it is unfortunately wrong. Since I just got finished writing about 10 pages of explanation for my upcoming book, I thought I’d post a shortened form here and hopefully help clear things up a little. This is going to be a little bit of a whirlwind, focused on the simplest case. If you want the gory details including performance improvements for large amounts of data, well, the book will be out later this year. :D
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I’m back in full book-writing mode, now working with Mugunth Kumar, who is brilliant. Go check out his stuff. Hopefully we’ll have something published and in all your hands by the end of the year. The book has taken up most of my writing time, so the blog will continue to be a bit quiet, but sometimes I like to answer a Stackoverflow question a bit more fully than I can there.
Today’s question is about laying out text without CTFramesetter. We’re going to take a whirlwind tour through some CoreText code to demonstrate this. It’s not quite what the OP was asking about, but it shows some techniques and I had it handy. I’ll be writing a whole chapter on Core Text soon.
The goal of this project was to make “pinch” view. It lays out text in a view, and where ever you touch, the text is pinched towards that point. It’s not meant to be really useful. Everything is done in drawRect:, which is ok in this case, since we only draw when we’re dirty, and when we’re dirty we have to redraw everything anyway. But in many cases, you’d want to do these calculations elsewhere, and only do final drawing in drawRect:.
We start with some basic view layout, and loop until we run out of text or run out of vertical space in the view.
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I’ve been playing with Core Text recently, and one of the things I wanted to do was layout text in an arbitrary CGPath. On Mac, you’d do this with NSLayoutManager, but iOS doesn’t have that so we have to build our own. I’ll discuss Core Text more later, but one of the steps along this problem is how to clip a CGRect to a CGPath. I found several discussions of finding CGPath intersections, all explaining the basic technique. Draw the things you care about into a bitmap context and then inspect the pixels to see where they overlap. Clear enough, but it was hard to find a small code sample that demonstrated this with Core Graphics.
For my purposes, I want the first full-height rectangle within the intersection of the line rectangle and the CGPath. Later I will expand this code to find all full-height rectangles within the intersection (there can be more than one), but this is enough to demonstrate the point.
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