UIView addSubview auto layout not working

问题:

I created a UIView programatically and add NSLayoutConstraint to it and it works and then add it as a subView of view controller's view. Right now I need to remove this view from superview and some time later add it again. But the layout won't work any more if I add it again using self.view addSubview. How to make the layout works again?

回答1:

You need to take care of some points while adding and removing views from auto layout.

There are two methods available in UIView.h class

// Allows you to perform layout before the drawing cycle happens. 
//   -layoutIfNeeded forces layout early
- (void)setNeedsLayout;
- (void)layoutIfNeeded;

Use these methods as per your requirement. So i suggest when ever you remove subview from view, Update constraint of superior view if it is required. And then call below method to reflect layout changes.

[self.view layoutIfNeeded];

Most cases above method will solve all layout related issues. However some time if complex structure is there i mean runtime changing behaviour of views.

Then override below method in your UIViewController, Perform all frame related changes in this method.

- (void)viewDidLayoutSubviews

回答2:

The problem is the sub view does not inherit the original view's size/frame, and there for adds the view as if it was stuck in the Any+Any size of 600x600. My solution, is to set the frame of the original view, and then let iOS do the remainder of the work.

[self.myOtherView setFrame:self.view.frame];   //Replace frame size with already resized view
[self.myOtherView setNeedsLayout];  //Tell iOS to autolayout the new sub view
[self.addSubView:self.myOtherView];  //Add it

回答3:

When you create constraints assign it to variables

@property (nonatomic, strong)NSLayoutConstraint *viewConstraintTop;
self.viewConstraintTop = [Your Constraint];

When you want to remove it from the superview remove the constraints

[self.viewConstraintTop autoRemove];

Remove your view and again while adding assign the constraint as

self.viewConstraintTop = [Your Constraint];