[WIP] Adding baseline align support

Pod/Classes/OAStackView+Traversal.h

@@ -18,6 +18,8 @@
 
 - (void)iterateVisibleViews:(void (^) (UIView *view, UIView *previousView))block;
 
+- (NSArray*)currentVisibleViews;
+
 - (UIView*)lastVisibleItem;
 
 - (NSLayoutConstraint*)firstViewConstraint;

Pod/Classes/OAStackView.h

@@ -55,7 +55,7 @@ typedef NS_ENUM(NSInteger, OAStackViewAlignment) {
    */
   OAStackViewAlignmentLeading,
   OAStackViewAlignmentTop = OAStackViewAlignmentLeading,
-  OAStackViewAlignmentFirstBaseline, // Valid for horizontal axis only
+  OAStackViewAlignmentFirstBaseline NS_ENUM_AVAILABLE_IOS(8_0), // Valid for horizontal axis only
 
   /* Center the items in a vertical stack horizontally
    or the items in a horizontal stack vertically
@@ -68,7 +68,8 @@ typedef NS_ENUM(NSInteger, OAStackViewAlignment) {
    */
   OAStackViewAlignmentTrailing,
   OAStackViewAlignmentBottom = OAStackViewAlignmentTrailing,
-  OAStackViewAlignmentLastBaseline, // Valid for horizontal axis only
+  OAStackViewAlignmentBaseline,
+  OAStackViewAlignmentLastBaseline = OAStackViewAlignmentBaseline, // Valid for horizontal axis only
 };
 
 // Keep older versions of the compiler happy

Pod/Classes/OAStackView.m

@@ -112,6 +112,7 @@ - (void)setAlignment:(OAStackViewAlignment)alignment {
 
   [self iterateVisibleViews:^(UIView *view, UIView *previousView) {
     [self.alignmentStrategy addConstraintsOnOtherAxis:view];
+    [self.alignmentStrategy alignView:view withPreviousView:previousView];
   }];
 }
 
@@ -134,6 +135,7 @@ - (void)setDistribution:(OAStackViewDistribution)distribution {
   [self iterateVisibleViews:^(UIView *view, UIView *previousView) {
     [self.alignmentStrategy addConstraintsOnOtherAxis:view];
     [self.distributionStrategy alignView:view afterView:previousView];
+    [self.alignmentStrategy alignView:view withPreviousView:previousView];
   }];
 }
 
@@ -239,8 +241,10 @@ - (void)insertArrangedSubview:(UIView *)view atIndex:(NSUInteger)stackIndex newI
   }
 
   [self.distributionStrategy alignView:view afterView:previousView];
+  [self.alignmentStrategy alignView:view withPreviousView:previousView];
   [self.alignmentStrategy addConstraintsOnOtherAxis:view];
   [self.distributionStrategy alignView:nextView afterView:view];
+  [self.alignmentStrategy alignView:nextView withPreviousView:view];
 }
 
 - (void)removeViewFromArrangedViews:(UIView*)view permanently:(BOOL)permanently {

Pod/Classes/OAStackViewAlignmentStrategy.h

@@ -15,6 +15,8 @@
 + (OAStackViewAlignmentStrategy*)strategyWithStackView:(OAStackView *)stackView;
 
 - (void)addConstraintsOnOtherAxis:(UIView*)view;
-- (void)removeAddedConstraints;;
+- (void)alignView:(UIView*)view withPreviousView:(UIView*)previousView;
+
+- (void)removeAddedConstraints;
 
 @end

Pod/Classes/OAStackViewAlignmentStrategy.m

@@ -20,6 +20,16 @@ @interface OAStackViewAlignmentStrategyLeading : OAStackViewAlignmentStrategy
 @interface OAStackViewAlignmentStrategyCenter: OAStackViewAlignmentStrategy
 @end
 
+@interface OAStackViewAlignmentStrategyBaseline: OAStackViewAlignmentStrategy
+- (NSLayoutAttribute)baselineAttribute;
+@end
+
+@interface OAStackViewAlignmentStrategyLastBaseline: OAStackViewAlignmentStrategyBaseline
+@end
+
+@interface OAStackViewAlignmentStrategyFirstBaseline: OAStackViewAlignmentStrategyBaseline
+@end
+
 @interface OAStackViewAlignmentStrategy ()
 @property(nonatomic, weak) OAStackView *stackView;
 @property(nonatomic) NSMutableArray *constraints;
@@ -47,7 +57,15 @@ + (OAStackViewAlignmentStrategy*)strategyWithStackView:(OAStackView *)stackView
     case OAStackViewAlignmentCenter:
       cls = [OAStackViewAlignmentStrategyCenter class];
       break;
-
+
+    case OAStackViewAlignmentBaseline:
+      cls = [OAStackViewAlignmentStrategyLastBaseline class];
+      break;
+
+    case OAStackViewAlignmentFirstBaseline:
+      cls = [OAStackViewAlignmentStrategyFirstBaseline class];
+      break;
+
     default:
       break;
   }
@@ -75,7 +93,14 @@ - (void)addConstraintsOnOtherAxis:(UIView*)view {
   id arr = [self constraintsalignViewOnOtherAxis:view];
   [self.constraints addObjectsFromArray:arr];
 
-  [self.stackView addConstraints:arr];
+  if (arr) { [self.stackView addConstraints:arr]; }
+}
+
+- (void)alignView:(UIView*)view withPreviousView:(UIView*)previousView {
+  id arr = [self constraintsAlignView:view afterPreviousView:previousView];
+  [self.constraints addObjectsFromArray:arr];
+
+  if (arr) { [self.stackView addConstraints:arr]; }
 }
 
 - (NSMutableArray *)constraints {
@@ -93,6 +118,8 @@ - (void)removeAddedConstraints {
 
 - (NSArray*)constraintsalignViewOnOtherAxis:(UIView*)view { /* subclassing */ return nil; }
 
+- (NSArray*)constraintsAlignView:(UIView *)view afterPreviousView:(UIView*)afterView { /* subclassing */ return nil; }
+
 @end
 
 @implementation OAStackViewAlignmentStrategyFill
@@ -150,3 +177,44 @@ - (NSArray*)constraintsalignViewOnOtherAxis:(UIView*)view {
 }
 
 @end
+
+@implementation OAStackViewAlignmentStrategyBaseline
+
+- (NSArray*)constraintsalignViewOnOtherAxis:(UIView*)view {
+  id constraintString = [NSString stringWithFormat:@"%@:|-(>=0@750)-[view]-(>=0@750)-|", [self otherAxisString]];
+
+  return [NSLayoutConstraint constraintsWithVisualFormat:constraintString
+                                                 options:0
+                                                 metrics:nil
+                                                   views:NSDictionaryOfVariableBindings(view)];
+}
+
+- (NSArray*)constraintsAlignView:(UIView *)view afterPreviousView:(UIView*)afterView {
+  if (!view  || !afterView) { return nil; }
+
+  return @[[NSLayoutConstraint constraintWithItem:view
+                                        attribute:[self baselineAttribute]
+                                        relatedBy:NSLayoutRelationEqual toItem:afterView
+                                        attribute:[self baselineAttribute] multiplier:1.0f
+                                         constant:0.0f]];
+}
+
+- (NSLayoutAttribute)baselineAttribute
+{
+    return NSLayoutAttributeBaseline;
+}
+
+@end
+
+@implementation OAStackViewAlignmentStrategyFirstBaseline
+
+- (NSLayoutAttribute)baselineAttribute
+{
+    return NSLayoutAttributeFirstBaseline;
+}
+
+@end
+
+@implementation OAStackViewAlignmentStrategyLastBaseline
+
+@end