Add constraint offset

Author: lauraskelton

JazzHands.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name         = 'JazzHands'
-  s.version      = '2.0.3'
+  s.version      = '2.0.4'
   s.summary      = 'Simple keyframe animations for scrolling intros.'
   s.homepage     = 'https://github.com/IFTTT/JazzHands'
   s.author       = { 

JazzHands/IFTTTAnimatedPagingScrollViewController.h

@@ -32,5 +32,9 @@
 - (void)keepView:(UIView *)view onPage:(CGFloat)page withAttribute:(IFTTTHorizontalPositionAttribute)attribute;
 - (void)keepView:(UIView *)view onPages:(NSArray *)pages withAttribute:(IFTTTHorizontalPositionAttribute)attribute;
 - (void)keepView:(UIView *)view onPages:(NSArray *)pages atTimes:(NSArray *)times withAttribute:(IFTTTHorizontalPositionAttribute)attribute;
+- (void)keepView:(UIView *)view onPages:(NSArray *)pages withAttribute:(IFTTTHorizontalPositionAttribute)attribute offset:(CGFloat)offset;
+- (void)keepView:(UIView *)view onPages:(NSArray *)pages atTimes:(NSArray *)times withAttribute:(IFTTTHorizontalPositionAttribute)attribute offset:(CGFloat)offset;
+- (void)keepView:(UIView *)view onPages:(NSArray *)pages withOffsets:(NSArray *)offsets withAttribute:(IFTTTHorizontalPositionAttribute)attribute;
+- (void)keepView:(UIView *)view onPages:(NSArray *)pages atTimes:(NSArray *)times withOffsets:(NSArray *)offsets withAttribute:(IFTTTHorizontalPositionAttribute)attribute;
 
 @end

JazzHands/IFTTTAnimatedPagingScrollViewController.m

@@ -206,6 +206,16 @@ - (void)keepView:(UIView *)view onPages:(NSArray *)pages withAttribute:(IFTTTHor
 }
 
 - (void)keepView:(UIView *)view onPages:(NSArray *)pages atTimes:(NSArray *)times withAttribute:(IFTTTHorizontalPositionAttribute)attribute
+{
+    [self keepView:view onPages:pages atTimes:times withAttribute:attribute offset:0.f];
+}
+
+- (void)keepView:(UIView *)view onPages:(NSArray *)pages withAttribute:(IFTTTHorizontalPositionAttribute)attribute offset:(CGFloat)offset
+{
+    [self keepView:view onPages:pages atTimes:pages withAttribute:attribute offset:offset];
+}
+
+- (void)keepView:(UIView *)view onPages:(NSArray *)pages atTimes:(NSArray *)times withAttribute:(IFTTTHorizontalPositionAttribute)attribute offset:(CGFloat)offset
 {
     NSAssert((pages.count == times.count), @"Make sure you set a time for each position.");
 
@@ -217,7 +227,7 @@ - (void)keepView:(UIView *)view onPages:(NSArray *)pages atTimes:(NSArray *)time
                                                                               toItem:self.contentView
                                                                            attribute:NSLayoutAttributeLeft
                                                                           multiplier:1.f
-                                                                            constant:0.f];
+                                                                            constant:offset];
     [self.contentView addConstraint:xPositionConstraint];
     // TODO: set constraint type for animation initializer
     IFTTTScrollViewPageConstraintAnimation *xPositionAnimation = [IFTTTScrollViewPageConstraintAnimation animationWithSuperview:self.contentView
@@ -234,6 +244,41 @@ - (void)keepView:(UIView *)view onPages:(NSArray *)pages atTimes:(NSArray *)time
     [self.scrollViewPageConstraintAnimations addObject:xPositionAnimation];
 }
 
+- (void)keepView:(UIView *)view onPages:(NSArray *)pages withOffsets:(NSArray *)offsets withAttribute:(IFTTTHorizontalPositionAttribute)attribute
+{
+    [self keepView:view onPages:pages atTimes:pages withOffsets:offsets withAttribute:attribute];
+}
+
+- (void)keepView:(UIView *)view onPages:(NSArray *)pages atTimes:(NSArray *)times withOffsets:(NSArray *)offsets withAttribute:(IFTTTHorizontalPositionAttribute)attribute
+{
+    NSAssert((pages.count == times.count) && (pages.count == offsets.count), @"Make sure you set a time and offset for each position.");
+    
+    view.translatesAutoresizingMaskIntoConstraints = NO;
+    
+    NSLayoutConstraint *xPositionConstraint = [NSLayoutConstraint constraintWithItem:view
+                                                                           attribute:[self layoutAttributeFromPositionAttribute:attribute]
+                                                                           relatedBy:NSLayoutRelationEqual
+                                                                              toItem:self.contentView
+                                                                           attribute:NSLayoutAttributeLeft
+                                                                          multiplier:1.f
+                                                                            constant:0.f];
+    [self.contentView addConstraint:xPositionConstraint];
+    // TODO: set constraint type for animation initializer
+    IFTTTScrollViewPageConstraintAnimation *xPositionAnimation = [IFTTTScrollViewPageConstraintAnimation animationWithSuperview:self.contentView
+                                                                                                                     constraint:xPositionConstraint
+                                                                                                                      pageWidth:self.pageWidth
+                                                                                                                      attribute:attribute];
+    
+    for (NSUInteger i = 0; i < pages.count; i++) {
+        [xPositionAnimation addKeyframeForTime:(CGFloat)[(NSNumber *)times[i] floatValue]
+                                          page:(CGFloat)[(NSNumber *)pages[i] floatValue]
+                                      constant:(CGFloat)[(NSNumber *)offsets[i] floatValue]];
+    }
+    
+    [self.animator addAnimation:xPositionAnimation];
+    [self.scrollViewPageConstraintAnimations addObject:xPositionAnimation];
+}
+
 - (CGFloat)centerXMultiplierForPage:(CGFloat)page
 {
     return [self multiplierForPage:page withAttribute:IFTTTHorizontalPositionAttributeCenterX];

JazzHands/IFTTTScrollViewPageConstraintAnimation.h

@@ -22,5 +22,7 @@ typedef NS_ENUM(NSUInteger, IFTTTHorizontalPositionAttribute) {
 + (instancetype)animationWithSuperview:(UIView *)superview constraint:(NSLayoutConstraint *)constraint pageWidth:(CGFloat)pageWidth attribute:(IFTTTHorizontalPositionAttribute)attribute;
 - (void)addKeyframeForTime:(CGFloat)time page:(CGFloat)page;
 - (void)addKeyframeForTime:(CGFloat)time page:(CGFloat)page withEasingFunction:(IFTTTEasingFunction)easingFunction;
+- (void)addKeyframeForTime:(CGFloat)time page:(CGFloat)page constant:(CGFloat)constant;
+- (void)addKeyframeForTime:(CGFloat)time page:(CGFloat)page constant:(CGFloat)constant withEasingFunction:(IFTTTEasingFunction)easingFunction;
 
 @end

JazzHands/IFTTTScrollViewPageConstraintAnimation.m

@@ -7,13 +7,15 @@
 //
 
 #import "IFTTTScrollViewPageConstraintAnimation.h"
+#import "IFTTTFilmstrip.h"
 
 @interface IFTTTScrollViewPageConstraintAnimation ()
 
 @property (nonatomic, strong) UIView *superview;
 @property (nonatomic, strong) NSLayoutConstraint *constraint;
 @property (nonatomic, assign) CGFloat initialConstraintConstant;
 @property (nonatomic, assign) IFTTTHorizontalPositionAttribute attribute;
+@property (nonatomic, strong) IFTTTFilmstrip *constantFilmstrip;
 
 @end
 
@@ -27,6 +29,7 @@ - (instancetype)initWithSuperview:(UIView *)superview constraint:(NSLayoutConstr
         _initialConstraintConstant = constraint.constant;
         _pageWidth = pageWidth;
         _attribute = attribute;
+        _constantFilmstrip = [IFTTTFilmstrip new];
     }
     return self;
 }
@@ -46,6 +49,18 @@ - (void)addKeyframeForTime:(CGFloat)time page:(CGFloat)page withEasingFunction:(
     [self addKeyframeForTime:time value:@(page) withEasingFunction:easingFunction];
 }
 
+- (void)addKeyframeForTime:(CGFloat)time page:(CGFloat)page constant:(CGFloat)constant
+{
+    [self addKeyframeForTime:time value:@(page)];
+    [self.constantFilmstrip setValue:@(constant) atTime:time];
+}
+
+- (void)addKeyframeForTime:(CGFloat)time page:(CGFloat)page constant:(CGFloat)constant withEasingFunction:(IFTTTEasingFunction)easingFunction
+{
+    [self addKeyframeForTime:time value:@(page) withEasingFunction:easingFunction];
+    [self.constantFilmstrip setValue:@(constant) atTime:time withEasingFunction:easingFunction];
+}
+
 - (void)animate:(CGFloat)time
 {
     if (!self.hasKeyframes) return;
@@ -64,7 +79,12 @@ - (void)animate:(CGFloat)time
             break;
     }
 
-    self.constraint.constant = (offset + page) * self.pageWidth + self.initialConstraintConstant;
+    CGFloat constant = 0.f;
+    if (!self.constantFilmstrip.isEmpty) {
+        constant = (CGFloat)[(NSNumber *)[self.constantFilmstrip valueAtTime:time] floatValue];
+    }
+    
+    self.constraint.constant = (offset + page) * self.pageWidth + self.initialConstraintConstant + constant;
     [self.superview layoutIfNeeded];
 }