Thursday, March 13, 2014

Percentage based layouts using (mostly) Xcode IB and Autolayout

The Xcode lnterface Builder (IB) doesn't provide a clear way to handle a percentage based layout - for example, a screen where one view takes up 25% of the width of the screen, and the other view gets the rest.

|                    |                                              |
|                    |                                              |
|                    |                                              |
|        A         |                       B                     |
|                    |                                              |
|                    |                                              |
|                    |                                              |

Here's one way to use IB for all but a few lines of code.  (based on ideas from this stackoverflow post.)

For "view B", using Xcode IB, I put constraints on the top, right, bottom, and left
For "view A", using Xcode IB, I put constraints on the top, left, bottom, and then set the width to a fixed size.  I edited the width constraint of "view A", and checked the "placeholder remove at build time" checkbox.

then, in the view controller's viewDidLoad, I added these two lines:

    NSLayoutConstraint *c = [NSLayoutConstraint constraintWithItem:viewA

    [viewA.superview addConstraint:c];

This just makes viewA 25% of the size of it's superview.  Since viewB is tied to viewA's width, it also adjusts properly without having to specify extra constraints for it.

Tuesday, March 11, 2014

iOS 7.1 issues

x. Noticed that the tab bars don't work quite the same way.  I have an .xib that I use for both iPad and iPhone layouts.  With 7.1, the tab bar now appears to be larger on the iPad (56 pixels) but the .xib doesn't auto adjust the 'y' for the former size (which was 49 pixels).  What this does is make the tab bar looked clipped at the bottom on the iPad. 

The fix requires using autolayout to set up the tab bar.  Then it works for 7.1 and prior versions.   An alternative fix is checking the tab bar's y value in the view controller's viewWillLayoutSubviews method to make sure it is equal to viewController.view.frame.size.height - tabBar.frame.size.height;

x. In previous versions, setting the corner radius and border on a layer would implicitly mask that layer to the corner arcs.  This is no longer the case in 7.1.  Now, if you set the background color of a UIView, and then set the corner radius and a border, the border will show the corner arcs, but the background color will extend to the square corners.

x. Not sure if this is a 7.1 only, issue but noted that an application that used to work okay is now getting a weird autolayout error on the iPad when dismissing a modal view.  There's tons of unhelpful error diagnostics and it ends with:
Cannot find an outgoing row head for incoming head UILabel:0x1462c580.Width{id: 414}, which should never happen.'

I saw a few mentions of this error on the web but no real help.  I was able to avoid the error by changing the constraints on one of the ViewControllers' UILabels.  Originally the UILabel was constrained to top right left with a fixed height.  It works if set to top width height centered x.     I doubt that this is the "real" solution, but I wasn't able to find anything else that seemed to be the issue.   (Ugh. There's three hours of my life I'll never get back).

Update: Ran into this error again and burned another six or so hours.  It seems related to percentage based views in autolayouts but I haven't been able to narrow it down much further than that.