Center views using *only* visual format? - ios

Question

I'm trying to center 2 views with different height vertically.
UILabel *view1 = [[UILabel alloc] init];
view1.backgroundColor = [UIColor redColor];
view1.text = #"view1\nline2";
view1.textAlignment = NSTextAlignmentCenter;
view1.numberOfLines = 0;
UILabel *view2 = [[UILabel alloc] init];
view2.backgroundColor = [UIColor greenColor];
view2.text = #"view2\nline2";
view2.textAlignment = NSTextAlignmentCenter;
view2.numberOfLines = 0;
[self.view addSubview:view1];
[self.view addSubview:view2];
NSDictionary *views = #{#"view1": view1, #"view2" : view2};
[self.view setTranslatesAutoresizingMaskIntoConstraints:NO];
for (UIView *view in views.allValues) {
[view setTranslatesAutoresizingMaskIntoConstraints:NO];
}
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-[view1]-[view2(==view1)]-|"
options:NSLayoutFormatAlignAllCenterY
metrics:nil views:views]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|-(>=20)-[view1(200)]-(>=20)-|"
options:NSLayoutFormatAlignAllCenterY
metrics:nil views:views]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|-(>=20)-[view2(100)]-(>=20)-|"
options:NSLayoutFormatAlignAllCenterY
metrics:nil views:views]];
This manages to make the centers of both aligned vertically, but they are at the bottom of the superview!
I want to center vertically not only relative to each other, also in the superview.
I added a constraint like this and it works:
[self.view addConstraint:
[NSLayoutConstraint constraintWithItem:view1
attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeCenterY
multiplier:1
constant:0]];
But I want to know, is this possible to achieve using only with visual format?

Answer 1

Yes, it's possible, but only by adding spacer views. So if you create a couple of views, lets call them spacer1 and spacer2, you can center view1 with this string,
#"V:|[spacer1][view1][spacer2(==spacer1)]|"
This assumes that view1 has a fixed height. I wouldn't recommend doing it this way though, I would just use the code you show at the bottom of your post.

Answer 2

What about calculating the Y in "metrics" ?
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|-centerY-[view1(200)]-(>=20)-|"
options:NSLayoutFormatAlignAllCenterY
metrics:#{#"centerY": #(CGRectGetHeight(self.view.frame)/2.0 - 100)}
views:views]];