Cocoa Autolayout itself is awesome, the way a developer implements it well isn’t so awesome. ZWPLayout is a small set of utilities to make autolayout as simple as c = m * x + b.
Bear with us as we try to make this documentation as complete as possible.
- Make autolayout code more readable
- Make autolayout code more concise
- Make autolayout code fun
ZWPLayout is just another string syntax that results in NSLayoutConstraints getting added into your views. Why another string syntax? Strings are the shortest possible way to implement complex layout code while keeping it readable, concise and fun. If you would rather a compile time check we recommend you check out the Masonry project as it uses method chaining to obtain compile time checks.
ZWPLayout installs two API methods into UIView:
- (ZWPLayoutViewConstraintsSet *)constrainToView:(UIView *)otherView formula:(NSString *)formula, …
- (ZWPLayoutViewConstraintsSet *)constrainWithFormula:(NSString *)formula, …
constrainToView:formula: allows you to constrain the calling view to another view with the specified formula. In this situation the "left hand" will be self and the "right hand" will be the view passed in.
constrainWithFormula: allows you to constrain the calling view to itself. This is useful for constraints that are not reliant on another view, such as min/max dimensions.
Each method takes a formula which is a string constaint with format specifiers just like stringWithFormat: so you can easy put in constants.
Each method also returns a ZWPLayoutViewConstraintsSet which is keeps track of all the constraints that were added for that particular formula as well as the view in which the constraints were added to. ZWPLayoutViewConstraintsSet has a enabled property which allows you to enable or disable constraints based on a formula super quick.
Writing forumla’s takes a little while to get into, though when in doubt it’s simply just c = mx + b. Formula’s thus should be left-attribute = multiplier * right-attribute + constant@priority where multiplier, constant and priority are optional. To specify more than one constraint in a single formula you simple separate them with commas.
These are all valid formula’s:
left = leftleft = left + 10left = left - 10left = left@749
And so are these, a bit more complex:
left = left, top = top, right = right + 10, bottom = bottomleft = centerX, top = 0.5 * height
Here are some use cases and full examples:
| Use Case | Example |
|---|---|
| Resize to fill superview | [view constrainToView:view.superview, formula:@"left = left, top = top, right = right, height = height"] |
| Resize to fill superview with 10px inset | [view constrainToView:view.superview, formula:@"left = left + 10, top = top + 10, right = right - 10, height = height - 10"] |
| 50% size of superview centered | [view constrainToView:view.superview, formula:@"width = 0.5 * width, height = 0.5 * height, centerX = centerX, centerY = centerY"] |
| Attributes |
|---|
| width |
| height |
| left |
| top |
| right |
| bottom |
| centerX |
| centerY |
| leading |
| trailing |
| baseline |
| Relations |
|---|
| = |
| >= |
| <= |
| Operators |
|---|
| * |
| + |
| - |
Add pod 'ZWPLayout', :git => 'https://github.com/zwopple/ZWPLayout.git' to your Podfile and then run pod install.
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Copyright (c) 2013 Zwopple Limited
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