Dynamically sized UIWebView in a UITableViewCell with auto layout - constraint violation
- by Orion Edwards
I've got a UITableViewCell which contains a UIWebView. The table view cell adjusts it's height depending on the web view contents.
I've got it all working fine, however when the view loads, I get a constraint violation exception in the debugger (the app continues running and functionally works fine, but I'd like to resolve this exception if possible).
How I've got it set up:
The TableView sets the cell height like this:
-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
if(indexPath.section == 0) {
[_topCell layoutIfNeeded];
CGFloat finalHeight = [_topCell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;
return finalHeight + 1;
}
The cell constraints are as follows:
Arbitrary 7px offset from the cell's contentView (top) to the webView
Web view has arbitrary fixed height constraint of 62px (will expand later once content loads)
Arbitrary 8px offset from the webView to the cell's contentView (bottom)
in my viewDidLoad, I tell the webView to go and load a URL, and in the webViewDidFinishLoad, I update the web view height constraint, like this
-(void)webViewDidFinishLoad:(UIWebView *)webView {
CGSize fittingSize = [webView sizeThatFits:CGSizeZero];
// fittingSize is approx 500
[self.tableView beginUpdates];
// Exceptions happen on the following line setting the constant
_topCell.webViewHeightConstraint.constant = fittingSize.height;
[_topCell layoutSubviews];
[self.tableView endUpdates];
}
The exception looks like this:
Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"<NSLayoutConstraint:0x10964b250 V:[webView(62)] (Names: webView:0x109664a00 )>",
"<NSLayoutConstraint:0x109243d30 V:|-(7)-[webView] (Names: webView:0x109664a00, cellContent:0x1092436f0, '|':cellContent:0x1092436f0 )>",
"<NSLayoutConstraint:0x109243f80 V:[webView]-(8)-| (Names: cellContent:0x1092436f0, webView:0x109664a00, '|':cellContent:0x1092436f0 )>",
"<NSAutoresizingMaskLayoutConstraint:0x10967c210 h=--& v=--& V:[cellContent(78)] (Names: cellContent:0x1092436f0 )>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x10964b250 V:[webView(62)] (Names: webView:0x109664a00 )>
This seems a bit weird. It's implied that the constraint which sets the height of the web view is going to be broken, however the web view does get it's height correctly set, and the tableview renders perfectly well.
From my guesses, it looks like the newly increased web view height constraint (it's about 500px after the web view loads) is going to conflict with the <NSAutoresizingMaskLayoutConstraint:0x10967c210 h=--& v=--& V:[cellContent(78)] setting the cell height to 78 (put there by interface builder). This makes sense, however I don't want that cell content to have a fixed height of 78px, I want it to increase it's height, and functionally, it actually does this, just with these exceptions.
I've tried setting _topCell.contentView.translatesAutoresizingMaskIntoConstraints = NO; to attempt to remove the NSAutoresizingMaskLayoutConstraint - this stops the exceptions, but then all the other layout is screwed up and the web view is about 10px high in the middle of the table view for no reason.
I've also tried setting _topCell.contentView.autoresizingMask |= UIViewAutoresizingFlexibleHeight; in the viewDidLoad to hopefully affect the contentView 78px height constraint, but this has no effect
Any help would be much appreciated
