On 10 Dec 2013, at 8:58 AM, Alex Zavatone wrote:
> I've just run across a nasty behaviour where with AutoLayout on iOS 7,
> sometimes a view will not appear at all after a segue.
>
> The scary thing is that this is intermittent, and will either happen all the
> time for a build or never for a build.
>
> Turning off AutoLayout appears to fix the issue, but I need to test more.
>
> This is verified under Xcode 5.0.2 and iOS7 on both the simulator and on an
> iPhone5.
>
> Has anyone else seen this?
I've seen this when a constraint chain either pushes the view off-screen or
collapses it to zero on one axis or the other. The conflict might not strike
every time, because autolayout's response is indeterminate (other than logging
the problem), and you've mostly been lucky.
If you're developing for iOS 7, you're running Xcode 5.x, and I pray you've set
the file for the Xcode 5 file type. Using the controls at the bottom-right of
the Storyboard canvas, set the idiom to iOS 7. Open the Assistant editor and
choose Preview. See what happens as you fiddle around with orientation and
screen size, again with those controls at bottom-right. If something
disappears, select it in the document outline (left side of the canvas,
expandable with the button at bottom-left), and see what the Size inspector
says.
If that doesn't help, see what repeating those variations in the iOS (7)
Simulator does. Some autolayout surprises show up only on a (simulated) device.
But if I'm right, then surely you'd have gotten warnings, both in the console
at runtime, and in the form of yellow and red badges in the document outline
next to the controller names. (Click one and get a list of issues; clicking one
of those will get you a popover offering solutions. And, the scene itself would
show in yellow the layout each view _ought_ to have if autolayout were fired.
You'd have mentioned this, so all I can say is that in my own experience, this
the only way I saw what you're seeing.
One approach that helped me was to use the elegantly-named Editor > Resolve
Auto Layout Issues submenu to clear out all the constraints in the scene, and
then generate IB's guess at what the constraints ought to be. The result is
unlikely to be good enough for release (try the orientations, idioms, and sizes
to see), but at least you'll have a fresh constraint set to work from.
— F
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