#purplish_layout – a RubyMotion wrapper for Auto Layout on iOS and OS X
Ruby lends itself to creating a nice DSL for Auto Layout, so why not? I have been using this for both iOS and OS X apps since mid-2014.
Use it with visual format strings:
['celf', inner_view, 'l', post_count_label].constraints do |celf, l, _|
celf.h '|[l]|'
celf.v '|-m-[l]-m-|', {'m' => 7}
end
You can also create constraint objects yourself. This is equivalent to the previous example:
['celf', inner_view, 'l', post_count_label].constraints do |celf, l, _|
celf.left = l.left
celf.right = l.right
l.top = celf.top + 7
l.bottom = celf.bottom - 7
end
Send #constraints
with a block to an array with an even number of elements. They should be pairs – the name (a String
) to be used in the format strings in the block, followed by the view it represents.
If there are n views involved, there should be n*2 elements in the array. The block takes n+1 arguments, and the last object is the dictionary mapping generated from the array (usually unused) and the rest of the elements are constraint proxy objects representing each view, in the order specified in the array.
To avoid confusion, it's best to keep the variable names in the block the same as the string names in the array.
With the exception of the first view listed in the array, translatesAutoresizingMaskIntoConstraints
is automatically set to false
for every view, so you'll want to specify the outermost view as the first pair.
A multipler can be supplied:
l.width = celf.width * 0.5
The attributes are available as :left
, :right
, :top
, :bottom
, :leading
, :trailing
, :width
, :height
, :center_x
, :center_y
and :baseline
.
You can mix the 2 creation methods:
['celf', inner_view, 'l', post_count_label].constraints do |celf, l, _|
celf.left = l.left
celf.right = l.right
celf.v '|-m-[l]-m-|', {'m' => 7}
end
When specifying options argument describing the attribute and direction of layout, you can also use symbols such as :align_center_y
(for NSLayoutFormatAlignAllCenterY
). They are interchangeable. The options are available as :align_left
, :align_right
, :align_top
, :align_bottom
, :align_leading
, :align_trailing
, :align_center_x
, :align_center_y
, :align_baseline
.
ie. these are equivalent:
cv.h '|[v1][v2][v3]|', nil, NSLayoutFormatAlignAllCenterY
cv.h '|[v1][v2][v3]|', nil, :align_center_y
You can write equality “statements” in a single line:
b0.center_y = b1.center_y = b2.center_y = b3.center_y = b4.center_y
You can specify the priority of a constraint using the ** operator:
b0.center_y = b1.center_y ** (UILayoutPriorityRequired-1)
(b0 ** (UILayoutPriorityRequired-1)).center_y = b1.center_y
(b0 ** (UILayoutPriorityRequired-1)).width = 10
The 1st and 2nd lines in the last example are equivalent, but the 3rd line — which has a constant on the right hand side — is an example where the priority has to be assigned on the left hand side of the expression.
There are 2 attributes in the constraint proxies that you would occasionally find useful:
last_constraint
returns the lastNSLayoutConstraint
created. It's useful if you want to hold on to aNSLayoutConstraint
and modify it in an animation.next_priority
sets the priority for the nextNSLayoutConstraint
you create. It has the same effect as the ** operator.
When working with arrays of elements, instead of doing this:
['tb', toolbar, 'b0', btns[0], 'b1', btns[1], 'b2', btns[2], 'b3', btns[3], 'b4', btns[4], 'b5', btns[5], 'b6', btns[6], 'b7', btns[7], 'b8', btns[8], 'b9', btns[9], 'b10', btns[10], 'b11', btns[11], 'b12', btns[12]].constraints do |tb, b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12, _|
b0.width = b1.width = b2.width = b3.width = b4.width = b5.width = b6.width = b7.width = b8.width = b9.width = b10.width = b11.width = b12.width
end
or:
['tb', toolbar, 'b0', btns[0], 'b1', btns[1], 'b2', btns[2], 'b3', btns[3], 'b4', btns[4], 'b5', btns[5], 'b6', btns[6], 'b7', btns[7], 'b8', btns[8], 'b9', btns[9], 'b10', btns[10], 'b11', btns[11], 'b12', btns[12]].constraints do |tb, b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12, _|
[b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12].constraint_same_width
end
You can do this:
['tb', toolbar, 'buttons', btns].constraints do |tb, buttons, _|
buttons.constraint_same_width
buttons.constraint_same_height
end
#constraints
automatically wrap arrays of views with another array of proxy objects.
1. In a better world, the first code example would have been:
[inner_view, post_count_label].constraints do |celf, l, _|
celf.h '|[l]|'
celf.v '|-m-[l]-m-|', {'m' => 7}
end
But since Proc#parameters
isn't available, the syntax to invoke constraints requires duplication of names. This syntax can be improved when Proc#parameters
is available.
2. In RubyMotion, local variables aren't shadowed correctly by dynamic variables. So try not to use the same names for the block args as the variables holding your views. Referring to the 1st example, if we use post_count_label
instead of l
:
['celf', inner_view, 'post_count_label', post_count_label].constraints do |celf, post_count_label, _|
celf.h '|[post_count_label]|'
celf.v '|-m-[post_count_label]-m-|', {'m' => 7}
end
#At this point, after the block, post_count_label is the constraint proxy, and not the label as one might expect.
- Add this to your
Gemfile
:gem 'purplish-layout'
- Run
bundle install
BSD. See LICENSE file.
- Email: hboon@motionobj.com
- Web: http://hboon.com/purplish-layout
- Twitter: http://twitter.com/hboon