Advice needed on moving UIViews with NSLayoutConstraints - ios

Question

From the images below, when the user taps on view1 I have view2 and view3 slide down to the footer, being effectively pulled by setting the view3's constraint constant with the footer to 0(ish). I have my xib set up with the constraints as shown in the first image. The 2 most important of these [for me right now] are the view1View2 constraint and the view3Footer constraint
To achieve the slide down I've ended up setting a low priority for the view1view2 constraint and a higher priority for the view3Footer constrain, then updating the view3Footer constraint constant in an animateWithDuration
My problem is getting view2 and view3 to slide back up which, if I was using the same method, I'd achieve by setting the view1view2 constraint constant to 2.
I believe that the problem with the above slide up is the greater priority of the view3Footer constraint over the view1View2 constraint, Priorities seem only to be read only so I can't change these specifically. I understand that in setting constraints I'm only requesting the view positioning.
... I believe I might be using the wrong method entirely ...
Am I going about this in the right way at all? Do I have to get the constraint objects IBOutlet and rewrite them? If so, am I rewriting the priorities? Should I just be using >= for the constants with equal priorities, which doesn't seem to work. My code for simply animating down is below, which isn't much but apart from gesture recognisers, the set up is mainly in the xib
Any help is very much appreciated.
Thanks, Steve
For the slide-down:
[UIView animateWithDuration:0.9 animations:^{
_view3FooterConstraint.constant=2;
[self.view layoutIfNeeded];
} completion:^(BOOL finished){}];
UPDATE Also tried this setting priorities to be equal - can no longer achieve slide-down
_view3FooterConstraint.constant=2;
[self.view setNeedsUpdateConstraints];
[UIView animateWithDuration:0.9 animations:^{
[self.view layoutIfNeeded];
} completion:^(BOOL finished){}];
For the slide-up:
[UIView animateWithDuration:0.9 animations:^{
_view1View2Constraint.constant=2;
[self.view layoutIfNeeded];
} completion:^(BOOL finished){}];

Answer 1

I think I would do this by just adding and removing the 2 constraints that change (2's top constraint to 1, and 3's bottom constraint to the footer). Make sure all the views have explicit heights, and make IBOutlets to the 2 constraints I mentioned above. You really only need one of those at a time, but you need to add both in IB so you can make outlets to them. In viewDidLoad, I immediately remove the bottom one. This should work in portrait and landscape. The code I used was:
implementation ViewController {
IBOutlet NSLayoutConstraint *conBottom;
IBOutlet NSLayoutConstraint *conTop;
int pos;
}
-(void)viewDidLoad{
[super viewDidLoad];
pos = 0;
[self.view removeConstraint:conBottom];
[self.view layoutSubviews];
}
-(IBAction)togglePosition:(id)sender { //tap recognizer on view one action method
if (pos == 0) {
[self moveDown];
}else{
[self moveUp];
}
}
-(void)moveDown {
[self.view removeConstraint:conTop];
[self.view addConstraint:conBottom];
conBottom.constant=2;
[UIView animateWithDuration:0.9 animations:^{
[self.view layoutIfNeeded];
} completion:^(BOOL finished) {
pos = 1;
}];
}
-(void)moveUp {
[self.view removeConstraint:conBottom];
[self.view addConstraint:conTop];
conTop.constant=2;
[UIView animateWithDuration:0.9 animations:^{
[self.view layoutIfNeeded];
}completion:^(BOOL finished) {
pos = 0;
}];
}