Autolayout - adding and running constraint

Question

I have a view with 2 container views: one main one on top and one at the bottom.

When the app launches, the bottom one is hidden via a frame that goes beyond the screen height. The top one in the meantime occupies the entire app window.

When I decide to show that bottom container, I want the top container to decrease in height and the view of the controller in that main container to be impacted as well.

I tried to add a constraint programmatically and used layoutIfNeeded but nothing worked.

I'm new to this. I don't necessarily want the best answer but how I should approach this.

Thanks!!!!

-(void)showBottom {
    NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:self.bottomContainer attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.mainContainer attribute:NSLayoutAttributeTop multiplier:1.0f constant:49.0f];
    [self.view addConstraint:constraint];
}

So I want to call that method and have the constraint be applied. Not sure how I do this. This method is within the controller whose view holds the 2 containers. — user1732055
– user1732055, Commented Jan 18, 2014 at 1:39

Matt · Accepted Answer · 2014-01-18 01:45:30Z

1

You can try pinning objects with a Top Space to Superview constraint and animating it.

// .h
@property (weak, nonatomic) IBOutlet NSLayoutConstraint *topConstraint;

// .m
[UIView animateWithDuration:1.0 animations:^{
    self.topConstraint.constant = 0;
    [self.nView layoutIfNeeded];
}];

answered Jan 18, 2014 at 1:45

Matt

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5 Comments

user1732055 Over a year ago

Do I need an animation for this? Can't I just do what I did above and then call layoutIfNeeded?

uchuugaka Over a year ago

You can but it will just appear suddenly.

user1732055 Over a year ago

Thanks. Still having trouble with it. Will keep at it

user1732055 Over a year ago

Actually I have tried something else where I reassign the frame. It seems to work. Now my problem is that a table view from a controller embedded in the main container gets cut off and doesn't readjust. Have to figure that one out.

user1732055 Over a year ago

Found a way by adding a constraint via the storyboard on the table view and the bottom of the view.

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