Aha. Yes, I did notice that I couldn't make constraints involving e.g. the built-in textLabel object; it's as if it wasn't even in the interface.
The second part of your answer, that not being in the view hierarchy means the autolayout engine won't operate, is the answer to my original question; as I suspected, what I'm trying to do probably just can't be done. Ah, well. It was clever… I wonder if it would be worth my asking for a feature? Surely I'm not going to be the only one who would like to take a hierarchy of views that's *not* in the interface and ask it to exercise the constraint engine to see where everything ends up. m. On Nov 2, 2012, at 10:41 AM, Luke Hiesterman <luket...@apple.com> wrote: > > On Nov 2, 2012, at 10:22 AM, Matt Neuburg <m...@tidbits.com> > wrote: > >> >> On Nov 2, 2012, at 10:14 AM, Luke Hiesterman <luket...@apple.com> wrote: >> >>> UITableViewCell doesn't currently support autolayout >> >> I guess I'm having a little trouble understanding what that means. I am >> placing content interface inside the content view of a UITableViewCell and >> handing constraints to the cell, and autolayout is working perfectly on that >> content: the content is repositioned when the cell gets wider and narrower >> (interface rotates) and it is enlarged vertically when the height of the >> cell is set. So you must be using "support" in some refined sense that I >> don't grasp. Can you expand a little? Thx! - m. > > Direct attempts to put constraints on direct subviews of the cell will crash, > and any attempt to put a constraint on the frame of the cell itself wouldn't > make any sense because a cell is either A. in the table view, in which case > it's sized by the table view and not constraints, or B. it's not in the view > hierarchy, in which case the autolayout engine won't do anything for you. > > Luke > >> >>> , so no, you won't be able to have the constraints system calculate the >>> height for you. >>> >>> Luke >>> >>> On Nov 2, 2012, at 10:10 AM, Matt Neuburg <m...@tidbits.com> wrote: >>> >>>> >>>> On Nov 2, 2012, at 9:03 AM, Luke Hiesterman <luket...@apple.com> wrote: >>>> >>>>> Cells are sized according to the value returned from >>>>> heightForRowAtIndexPath: >>>> >>>> Obviously. And that is why I am calculating (in advance) the value that I >>>> will return from heightForRowAtIndexPath:. I've been doing that for years. >>>> The question is, though, can I now (iOS 6) have the constraints system >>>> somehow calculate that value for me, merely by putting the ultimate values >>>> into the labels of a test cell that isn't in the interface? >>>> >>>> The code I'm using now is at >>>> >>>> <https://github.com/mattneub/Programming-iOS-Book-Examples/blob/master/ch21p622variableHeights/ch21p622variableHeights/RootViewController.m> >>>> >>>> As you can see, I'm hard-coding the numbers in my precalc routine >>>> (viewDidLoad). Basically, I'm *guessing* what the constraints *will* do >>>> when I later give the cell height (using heightForRowAtIndexPath:) and the >>>> label resizes because of the constraints. What I'm saying is, how about if >>>> I perform the precalculation the opposite way, i.e. by resizing the label >>>> and letting it resize the cell? But I can't find a formula to do that. The >>>> code below (in this email) shows the sort of thing I've tried. m. >>>> >>>>> >>>>> On Nov 2, 2012, at 8:07 AM, Matt Neuburg <m...@tidbits.com> wrote: >>>>> >>>>>> Okay, I have this wild and crazy idea. I've got a UITableView with cells >>>>>> that have different heights. The cells' content consists almost entirely >>>>>> of UILabels, and the height of each cell depends on what's going to go >>>>>> into those labels - the cell needs to grow to accommodate the text of >>>>>> the labels. The way I've always done this in the past is to calculate >>>>>> how the labels will be drawn, using NSString sizeWithFont etc, and then >>>>>> lay out the labels and calculate the needed cell size. >>>>>> >>>>>> But it occurs to me that in theory constraints could do all the work for >>>>>> me. I'm already using constraints to resize the actual labels when the >>>>>> cell changes size to assume its final height, but maybe I could use >>>>>> constraints to *make* cell assume its final height based on the content >>>>>> of the labels. The cell is in a nib, so if there were just one label, >>>>>> the code might be something like this: >>>>>> >>>>>> NSArray* objs = [[UINib nibWithNibName:@"Cell" bundle:nil] >>>>>> instantiateWithOwner:nil options:nil]; >>>>>> Cell* cell = objs[0]; >>>>>> cell.bounds = CGRectMake(0,0,320,50); >>>>>> cell.lab.text = // whatever the actual content will be >>>>>> [cell.lab sizeToFit]; // or something :) >>>>>> >>>>>> The idea is that the label will assume its final size and the existing >>>>>> constraints will push the cell height larger as needed. Okay, but it >>>>>> isn't working; the cell isn't growing. >>>>>> >>>>>> My theory is that this probably *can't* work because the auto layout >>>>>> stuff doesn't kick in unless the view is actually in the interface, >>>>>> which (as you can see) it isn't. And probably not until the next run >>>>>> loop, either, which is not good enough; I need to run through a whole >>>>>> lot cells and do this, right now, to calculate all the cell heights in >>>>>> advance of the table appearing. >>>>>> >>>>>> So, am I right that this is just impossible, or is there some cool way >>>>>> to do it that I just haven't stumbled on yet? Thx - m. >>>>>> -- matt neuburg, phd = m...@tidbits.com, http://www.apeth.net/matt/ pantes anthropoi tou eidenai oregontai phusei Programming iOS 5! http://shop.oreilly.com/product/0636920023562.do RubyFrontier! http://www.apeth.com/RubyFrontierDocs/default.html TidBITS, Mac news and reviews since 1990, http://www.tidbits.com _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
