iOS6上的Autolayout问题：“应该从引擎中删除所有依赖约束，也可以从视图的依赖约束列表中删除”

Question

Has anyone encountered this warning message related with autolayout:

All dependent constraints should have been removed from the engine and also from the view's list of dependent constraints

Currently, we have some footerView with several buttons inside and they are hidden or showed depending on the need. We use full autolayout everywhere. Here's the method for hiding/showing this footerView:

- (void)hideFooterView:(BOOL)shouldHide {

  self.containerViewBottomConstraint.constant = shouldHide ? 0 : 50; // expand  containing view to fit to full screen OR make it smaller to fit with footerView

  [UIView animateWithDuration:1 animations:^{
    [self.view layoutIfNeeded]; // animate expanding screen height to full height
    [self.footerView setAlpha:(shouldHide ? 0 : 1)];
  } completion:nil];  
}

So, when this method is called for the first time then there's no error message. But after the second time mentioned warning appears in console. We can't ignore this warning because in other screens we are encountering crashes with private Apple method calls without any clue how to solve that:

[UILayoutContainerView nsis_shouldIntegralizeVariable:]: message sent to deallocated instance

here's another crash message:

[UILayoutContainerView nsis_valueOfVariable:didChangeInEngine:]: message sent to deallocated instance

I was unable to find anything useful related to "nsis_valueOfVariable:didChangeInEngine:" or "Autolayout dependent constraints" keywords on web. Any ideas?

UPDATE Commenting out line "[self.view layoutIfNeeded]" seems fixed the issue but then there will be no animation...

Answer 1

In my project also this issue came. I was getting same warning "All dependent constraints should have been removed from the engine and also from the view's list of dependent constraints".

As you told, when I ignored it and in other screens I got crashes, showing

[UILayoutContainerView nsis_shouldIntegralizeVariable:]: message sent to deallocated instance

I found that, in my case I was calling [self.view layoutIfNeeded] inside -(void)viewWillDisappear:(BOOL)animated . When I removed this out, the issue was fixed. No warnings and no crashes.

From this what I understood is, if we call layoutIfNeeded just before the view is being deallocated this warning will come. And in next screens it will cause crashing.

It took so much time to figure out this crash. That's why I am sharing my thoughts.

This may help someone.