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POUITableViewHeaderFooterView subclass with auto layout and section reloading won't work well together
 

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  1. POUITableViewHeaderFooterView subclass with auto layout and section reloading won't work well together
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    <p>I am trying to incorporate auto layout into my UITableViewHeaderFooterView subclass. The class is pretty basic, just two labels. This is the complete subclass: </p> <pre><code>@implementation MBTableDetailStyleFooterView static void MBTableDetailStyleFooterViewCommonSetup(MBTableDetailStyleFooterView *_self) { UILabel *rightLabel = [[UILabel alloc] init]; _self.rightLabel = rightLabel; rightLabel.translatesAutoresizingMaskIntoConstraints = NO; [_self.contentView addSubview:rightLabel]; UILabel *leftLabel = [[UILabel alloc] init]; _self.leftLabel = leftLabel; leftLabel.translatesAutoresizingMaskIntoConstraints = NO; [_self.contentView addSubview:leftLabel]; NSDictionary *views = NSDictionaryOfVariableBindings(rightLabel, leftLabel); NSArray *horizontalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"|-10-[leftLabel]-(&gt;=10)-[rightLabel]-10-|" options:0 metrics:nil views:views]; [_self.contentView addConstraints:horizontalConstraints]; // center views vertically in super view NSLayoutConstraint *leftCenterYConstraint = [NSLayoutConstraint constraintWithItem:leftLabel attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:_self.contentView attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]; [_self.contentView addConstraint:leftCenterYConstraint]; NSLayoutConstraint *rightCenterYConstraint = [NSLayoutConstraint constraintWithItem:rightLabel attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:_self.contentView attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]; [_self.contentView addConstraint:rightCenterYConstraint]; // same height for both labels NSLayoutConstraint *sameHeightConstraint = [NSLayoutConstraint constraintWithItem:leftLabel attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:rightLabel attribute:NSLayoutAttributeHeight multiplier:1 constant:0]; [_self.contentView addConstraint:sameHeightConstraint]; } + (BOOL)requiresConstraintBasedLayout { return YES; } - (id)initWithReuseIdentifier:(NSString *)reuseIdentifier { self = [super initWithReuseIdentifier:reuseIdentifier]; MBTableDetailStyleFooterViewCommonSetup(self); return self; } @end </code></pre> <p>This class is used as a footer in the first section in a tableView with 2 sections. The first section contains dynamic items. The second section has only one row, which is used to add new items to the first section. </p> <p>If there are no items in the first section I hide the footerView. So when I add the first new item I have to reload the section so the footerView appears. The code that does all this looks like this:</p> <pre><code>- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { [tableView deselectRowAtIndexPath:indexPath animated:YES]; if (indexPath.section == 1) { BOOL sectionNeedsReload = ([self.data count] == 0); // reload section when no data (and therefor no footer) was present before the add [self.data addObject:[NSDate date]]; NSIndexPath *newIndexPath = [NSIndexPath indexPathForRow:[self.data count]-1 inSection:0]; if (sectionNeedsReload) { [self.tableView reloadSections:[NSIndexSet indexSetWithIndex:0] withRowAnimation:UITableViewRowAnimationAutomatic]; } else { [self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationAutomatic]; } [self configureFooter:(MBTableDetailStyleFooterView *)[tableView footerViewForSection:0] forSection:0]; } } - (void)configureFooter:(MBTableDetailStyleFooterView *)footer forSection:(NSInteger)section { footer.leftLabel.text = @"Total"; footer.rightLabel.text = [NSString stringWithFormat:@"%d", [self.data count]]; } - (UIView *)tableView:(UITableView *)tableView viewForFooterInSection:(NSInteger)section { MBTableDetailStyleFooterView *footer = nil; if (section == 0 &amp;&amp; [self.data count]) { footer = [tableView dequeueReusableHeaderFooterViewWithIdentifier:@"Footer"]; [self configureFooter:footer forSection:section]; } return footer; } - (CGFloat)tableView:(UITableView *)tableView heightForFooterInSection:(NSInteger)section { CGFloat height = 0; if (section == 0 &amp;&amp; [self.data count]) { height = 20.0f; } return height; } </code></pre> <p>Nothing really fancy. However, <strong>as soon as <code>reloadSections:withRowAnimations:</code> is called on my tableView it throws an exception because it is "Unable to simultaneously satisfy constraints.".</strong> </p> <p>Somewhere the tableView added a translated auto resizing mask constraint to my footer. </p> <pre><code>( "&lt;NSLayoutConstraint:0x718a1f0 H:[UILabel:0x7189130]-(10)-| (Names: '|':_UITableViewHeaderFooterContentView:0x7188df0 )&gt;", "&lt;NSLayoutConstraint:0x7189e30 H:[UILabel:0x71892c0]-(&gt;=10)-[UILabel:0x7189130]&gt;", "&lt;NSLayoutConstraint:0x718a0a0 H:|-(10)-[UILabel:0x71892c0] (Names: '|':_UITableViewHeaderFooterContentView:0x7188df0 )&gt;", "&lt;NSAutoresizingMaskLayoutConstraint:0x7591ab0 h=--&amp; v=--&amp; H:[_UITableViewHeaderFooterContentView:0x7188df0(0)]&gt;" ) </code></pre> <p>When I replace <code>reloadSections:withRowAnimations:</code> with a call to <code>reloadData</code> no autoresizing mask constraint is added and everything works fine. </p> <p>The interesting thing is that the exception tells me that it tries to break the constraint <code>&lt;NSLayoutConstraint:0x7189e30 H:[UILabel:0x71892c0]-(&gt;=10)-[UILabel:0x7189130]&gt;</code></p> <p>But when I log the constraints in subsequent calls to <code>configureFooter:forSection:</code> this constraint still exists, but the auto resizing mask constraint is gone</p> <p>The constraints are exactly those that I have set up. </p> <pre><code>( "&lt;NSLayoutConstraint:0x718a0a0 H:|-(10)-[UILabel:0x71892c0] (Names: '|':_UITableViewHeaderFooterContentView:0x7188df0 )&gt;", "&lt;NSLayoutConstraint:0x7189e30 H:[UILabel:0x71892c0]-(&gt;=10)-[UILabel:0x7189130]&gt;", "&lt;NSLayoutConstraint:0x718a1f0 H:[UILabel:0x7189130]-(10)-| (Names: '|':_UITableViewHeaderFooterContentView:0x7188df0 )&gt;", "&lt;NSLayoutConstraint:0x718a3f0 UILabel:0x71892c0.centerY == _UITableViewHeaderFooterContentView:0x7188df0.centerY&gt;", "&lt;NSLayoutConstraint:0x718a430 UILabel:0x7189130.centerY == _UITableViewHeaderFooterContentView:0x7188df0.centerY&gt;", "&lt;NSLayoutConstraint:0x718a4b0 UILabel:0x71892c0.height == UILabel:0x7189130.height&gt;" ) </code></pre> <p>Where does this auto resizing mask constraint come from? Where does it go? </p> <p>Am I missing something? The first time I looked into auto layout was like a week ago, so this is totally possible.</p>
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    1. USMatthias Bauch
    1. USMatthias Bauch
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      1. UScroigsalvador
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    1. COquite a stumper, actually. did you ever figure this out?
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      1. USTomSwift
 

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