NSLayoutContraint to position a button in the center of a view - ios

Question

I am playing around with Constaints, they seems quite something :)
I would like to know, what will be the VisualString to position a button in the center (horizontally and vertically) of the view.
Should would I be using
NSLayoutContraint(item: attribute: relatedBy: toItem: attribute: multiplier: constant)

Answer 1

With Restraint you only need to do it:
let imageViewHorizontalConstraint = NSLayoutConstraint(
item: imageView,
attribute: .CenterX,
relatedBy: .Equal,
toItem: self,
attribute: .CenterX,
multiplier: 1.0,
constant: 0
)
let imageViewVerticalConstraint = NSLayoutConstraint(
item: imageView,
attribute: .CenterY,
relatedBy: .Equal,
toItem: self,
attribute: .CenterY,
multiplier: 1.0,
constant: 0
)
addConstraints([imageViewHorizontalConstraint, imageViewVerticalConstraint])
Without Visual Format
// Center horizontally
[self addConstraint:[NSLayoutConstraint constraintWithItem:centerView
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:self
attribute:NSLayoutAttributeCenterX
multiplier:1.0
constant:0.0]];
[self addConstraint:[NSLayoutConstraint constraintWithItem:centerView
attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual
toItem:self
attribute:NSLayoutAttributeCenterY
multiplier:1.0
constant:0.0]];
Visual Format
// Variables
NSDictionary *views = #{
#"view" : self.view,
#"superview" : self.view.superview,
};
NSDictionary *metrics = #{
#"width" : #(CGRectGetWidth(self.view.frame)),
#"height" : #(CGRectGetHeight(self.view.frame))
};
// Constraints
NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:#"H:[superview]-(<=1)-[view(width)]"
options:NSLayoutFormatAlignAllCenterY
metrics:metrics
views:views];
[self.view.superview addConstraints:constraints];
constraints = [NSLayoutConstraint constraintsWithVisualFormat:#"V:[superview]-(<=1)-[view(height)]"
options:NSLayoutFormatAlignAllCenterX
metrics:metrics
views:views];
[self.view.superview addConstraints:constraints];

Answer 2

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-[titleLabel]-|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(titleLabel)]];
[self.contentView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|-[titleLabel]-|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(titleLabel)]];
Edit :- This one will work better
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:[titleLabel]" options:NSLayoutFormatAlignAllCenterX metrics:nil views:NSDictionaryOfVariableBindings(titleLabel)]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:[titleLabel]" options:NSLayoutFormatAlignAllCenterY metrics:nil views:NSDictionaryOfVariableBindings(titleLabel)]];