OALayoutAnchor
is an effort to port the amazing NSLayoutAnchor introduced in iOS 9 to iOS 7.
OALayoutAnchor
is a 100% port of NSLayoutAnchor
to iOS 7, it aims to provide the same functionality to iOS 7, and rollback to NSLayoutAnchor
on iOS 9 and up.
To run the example project, clone the repo, and run pod install
from the Example directory first.
Usage is 100% compatible with NSLayoutAnchors
.:
Example Usage (Taken from apple websites):
// Creating constraints using NSLayoutConstraint
[NSLayoutConstraint
constraintWithItem:subview
attribute:NSLayoutAttributeLeading
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeLeadingMargin
multiplier:1.0
constant:0.0].active = YES;
[NSLayoutConstraint
constraintWithItem:subview
attribute:NSLayoutAttributeTrailing
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeTrailingMargin
multiplier:1.0
constant:0.0].active = YES;
The following constraint setup can be rewritten to the following:
// Creating the same constraints using Layout Anchors
UILayoutGuide *margin = self.view.layoutMarginsGuide;
[subview.leadingAnchor constraintEqualToAnchor:margin.leadingAnchor].active = YES;
[subview.trailingAnchor constraintEqualToAnchor:margin.trailingAnchor].active = YES;
For iOS 7, since active
property is not available on NSLayoutConstraint
the constraint set will be already installed. The bellow code shows the usage on iOS7:
// Creating the same constraints using Layout Anchors
UILayoutGuide *margin = self.view.layoutMarginsGuide;
[subview.leadingAnchor constraintEqualToAnchor:margin.leadingAnchor];
[subview.trailingAnchor constraintEqualToAnchor:margin.trailingAnchor];
For a better documentation please refer to apple docs.
OALayoutAnchor is available through CocoaPods. To install it, simply add the following line to your Podfile:
pod "OALayoutAnchor"
There are several unit tests covering most of the Equality constraints. Unit test for covering Greater than or Lesser than are coming next.
Test are currently running for iOS 8 only, test for iOS 7 are coming next.
The following a human readable text subscript (generated with specipy).
Since iOS7 NSLayoutConstraint
does not have an active
property, the category NSLayoutConstraint+SuppressActive
was introduced to make the usage of the constraints transparent between iOS7 and 8.
When using the bellow line:
[label1.leadingAnchor constraintEqualToAnchor:self.view.leadingAnchor constant:20].active = YES;
On iOS 8, the returned constraint is not active until we call .active = YES
on it. However, on iOS 7, since there is no active property on NSLayoutConstraint
. a method has been attached to the NSLayoutConstraint
to ignore the isActive
method calls.
That means that calling isActive
or active
on iOS 7 will not crash the app, these calls will just be ignored.
Since anchor UIView's properties are annotated with NS_AVAILABLE_IOS(9_0);
, it makes them unusable with swift when the app deployment target is less than iOS9.
The compiler will not allow the usage of anchor properties without guarding against the iOS version.
if #available(iOS 9.0, *) {
view.leftAnchor
} else {
// Fallback on earlier versions
}
In order to target this problem, OALayoutAnchor
contains a mirror of all the anchor properties. these properties are named with a prefix of oa_
var oa_leadingAnchor: NSLayoutXAxisAnchor! { get }
var oa_trailingAnchor: NSLayoutXAxisAnchor! { get }
var oa_leftAnchor: NSLayoutXAxisAnchor! { get }
... etc..
As an example, using oa_leadingAnchor
in iOS 9 and up, will forward the invocation to leadingAnchor
. On iOS 8 and 7, this call will use the layout anchor from OALayourAnchor
.
NSLayoutConstraint
active
property is also unusable in swift for any iOS less than 8. In order to address this issue please use oa_active
.
Using oa_active
will result in using active
on iOS 8,9 and doing nothing on iOS 7.
This is an example in swift:
view1.oa_widthAnchor.constraintEqualToConstant(100).oa_active = true
view1.oa_heightAnchor.constraintEqualToConstant(100).oa_active = true
view1.oa_centerXAnchor.constraintEqualToAnchor(self.view.oa_centerXAnchor).oa_active = true
view1.oa_centerYAnchor.constraintEqualToAnchor(self.view.oa_centerYAnchor).oa_active = true
The following would be nice to have for future versions
- Increase the test coverage for Greater than and Less Than
- Better Documentation
- Add tests for iOS 7
Omar Abdelhafith, [email protected]
OALayoutAnchor is available under the MIT license. See the LICENSE file for more info.