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Created by Martin Pilkington on 01/02/2013.
Please read the LICENCE.txt for licensing information
#import <Cocoa/Cocoa.h>
Methods to help working with constraints on an NSView
**Constraint Equation String Syntax**
This category contains the method -m3_addConstraintsFromEquations:substitutionViews:. While it looks simple, it actually provides an
extremely powerful and expressive way to create and add constraints to a view. Unfortunately the existing ways of creating layouts in code
are either inflexible or verbose. The visual syntax allows adding multiple constraints in a concise way, but does not allow for all possibilities
and limits you to a single axis at a time. The method syntax gives access to the full power of the autolayout system, but requires each
constraint be created individually. This category adds a third syntax, the constraint equation string syntax
Constraints represent equations of the form y = mx + c. The equation syntax allows you to define your constraints in a similar way. The
basic format is "$view.attributes =(@priority) multiplier($otherview.attributes) + constant". You can use these to build up an array of equation
strings that are passed in and used to create constraints.
Constraint equations can act upon the receiver and/or any views supplied via the substitution views argument. This argument can take either
an NSDictionary or an NSArray. Any substitution views MUST be children of the receiver (though need not be direct subviews).
Views are used in equations by writing a dollar sign, followed by the view name. The name will depend on the type of collection
passed in. If an NSDictionary was passed in, the view names are the keys of that dictionary. If an NSArray was passed in, the view names
are numbers from 0 to (array.count - 1). For example, for a dictionary @{@"foo":view1, @"bar":view2}, you would use "$foo" and "$bar" to
access the views. For an array @[view1, view2] you would instead use "$0" and "$1".
There are two special view names. The first of these is "$self" which refers to the receiver view. The third is "$all" which refers to all the
substitution views passed in (but does not include the receiver). This is useful if you want to apply constraints to a long list of subviews.
Finally, you can use key paths to access properties on the named views. The key path must result in a view being returned, but other than
that there are no restrictions. This is useful if the receiver has subviews stored in properties that you want to refer to, and saves having to
pass those in as a substitution variable
There are 14 attributes that can be used in constraint strings. The first 11 represent the layout attributes that you can use:
* left = NSLayoutAttributeLeft
* right = NSLayoutAttributeRight
* top = NSLayoutAttributeTop
* bottom = NSLayoutAttributeBottom
* leading = NSLayoutAttributeLeading
* trailing = NSLayoutAttributeTrailing
* width = NSLayoutAttributeWidth
* height = NSLayoutAttributeHeight
* centerX = NSLayoutAttributeCenterX
* centerY = NSLayoutAttributeCenterY
* baseline = NSLayoutAttributeBaseline
The other three are special attributes that expand to attribute lists (see the Lists section for more). These are:
* margins = (top, leading, bottom, trailing)
* size = (width, height)
* center = (centerX, centerY)
**Constants And Multipliers**
Constants and multipliers can be defined as integer or floating point values. They are used to modify the equation. By default the multiplier
is set to 1 and the constant to 0. If you leave either of these out of an equation the default will be used. Constants are prefixed by either the
+ or - symbol (unless they're standalone constants, in which case the + is not required for positive constants).
Multipliers can either be placed before or after the view property. If they are placed before, you must use the syntax "multipler($".
If they are placed after you must use the syntax "$ * multiplier". The multiplier must ALWAYS come before the constant.
There are three types of relationship possible with autolayout. Equals, less than or equal to and greater than or equal to. These are defined
in constraint strings as =, <= and >= respectively
Priorities are attached to the relationship in the equation syntax. The syntax is "relationship(@priority)". If you do not explicitly set a priority
it will be set to 1000 (i.e. required). For example, you might do "$self.width =(@250) 50", which adds a width constraint with a constant of 50
and a priority of 250 to the receiver.
A constraint string can represent multiple constraints. It does this through lists. Lists are defined as comma separated values within brackets.
For example, a constant list might be (0, 1, 2, 3) and a attribute list might be (top, bottom). As noted above, there are some special attributes
that are infact lists themselves. This simplifies some more common lists.
The components on the right hand side of the equation must have either a single value, or a list equal to the size of the list on the left hand
side. The easiest way to demonstrate this is through some examples. The following are all valid:
* $self.(width, height) = 10
* $self.(width, height) = (10, 5)
* $self.(width, height) = $x.width
* $self.(width, height) = $x.(width, height)
* $self.(width, height) = $x.(width, height) * 2 + 4
Note the last string will set the width to "x.width * 2 + 4" and the height to "x.height * 2 + 4". The following constraint strings are all invalid:
* $self.(width, height) = (10, 4, 5)
* $self.(width, height) = (10)
* $self.width = $x.(width, height)
Sometimes you may not want to specify constants for certain list items. To allow for this, constant lists let you specify "-" as the value.
For example, an equation "$self.super = (10, -, 10, -)" will only create two constraints and is equivalent to "$self.(top, bottom) = (10, 10)"
@interface NSView (M3AutolayoutExtensions)
Adds a subview to the receiver, with the initial superview constraints defined by the inset
@param aSubview The subview to add
@param aInsets The margin the subview should have from each edge of the receiver
- (void)m3_addSubview:(NSView *)aSubview marginsToSuperview:(NSEdgeInsets)aInsets;
Adds constraints representing the supplied equations to the subview
@param aConstraints An array of constraint equation strings
@param aSubstitutionViews A collection of substitution views to use in the constraint strings (either an NSArray or NSDictionary)
- (void)m3_addConstraintsFromEquations:(NSArray *)aEquations substitutionViews:(id)aSubstitutionViews;
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