Adding Autolayout programatically to existing autolayout Views added in xibs - objective-c

Question

I have a view like below which has auto layout set in xibs.
Now I need to add a error notification, which will animate from top and the existing views will shift down, like this image below.
I know I can do this easily by simply adding this error view in my existing view controller and managing its height constraints. But I have a couple of other views where I need to re-use this error view. So, now I have created a custom view for this error view. Now my main problem is adding this to my mainview programatically with autolayout. So I need to add the blue error view in my self.view and remove the top layout constraint of the green view and set its top to the blue error view. Make sense? Below is my code for error view and adding it to self.view. But even that doesn't work, am I doing anything wrong here. Any help is appreciated.
-(id)initWithdelegate:(id)parentSelf ForView:(UIView *)parentView
{
if (self = [super initWithFrame:CGRectMake(0, 0, 100, 100)])
{
// Initialization code
self=(ErrorView*)[[[NSBundle mainBundle] loadNibNamed:#"ErrorView" owner:nil options:nil]objectAtIndex:0];
self.delegate=parentSelf;
[parentView addSubview:self];
self.hidden = YES;
[self setConstraintsToParentView:parentView];
}
return self;
}
-(void)setConstraintsToParentView:(UIView *)parentView
{
[parentView setTranslatesAutoresizingMaskIntoConstraints:NO];
//Setting width equal to parentview
[parentView addConstraint:[NSLayoutConstraint constraintWithItem:self
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:parentView
attribute:NSLayoutAttributeWidth
multiplier:1
constant:0]];
//Setting fixed height of 50
[parentView addConstraint:[NSLayoutConstraint constraintWithItem:self
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationGreaterThanOrEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:1.0
constant:50]];
//Setting x pos to center
[parentView addConstraint:[NSLayoutConstraint constraintWithItem:self
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:parentView
attribute:NSLayoutAttributeCenterX
multiplier:1.0
constant:0.0]];
//Setting top position to self.view with constant 20
[parentView addConstraint:[NSLayoutConstraint constraintWithItem:self
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:parentView
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:20]];
}
I'm calling the errorView like this from my viewcontroller
myErrorView = [[ErrorView alloc]initWithdelegate:self ForView:self.view];

Answer 1

you can use identifier propertiy of constraints
NSArray *ArrayConstraint = yorlableorView.constraints;
for (NSLayoutConstraint *ob in ArrayConstraint)
{
if ([ob.identifier isEqualToString:#"yourIdentifier"])
{
ob.constant = 0 ;
// set your constant you want
}
}

Answer 2

Could you just add the error view as the top view with a height of 0 and then change the height constraint constant when you want to display it? You can animate this and it will simulate it pushing everything down, however with this approach it won't look like it is coming down from the top of the screen.
If you're happy with this approach you could just add a container view to your view with the buttons and tableview, then after you initialise the error view from the xib just assign it to the container, this will save you having to pass the parent view, adding it as a subview and adding the constraints programmatically in your error view class.
Let me know if need more detail or a concrete example. Hope this helps, good luck. Also just as an aside, you could look into Masonry, it makes adding constraints programmatically much easier.