From 13eb849e4a43139c64e35a5a738396d2c005478f Mon Sep 17 00:00:00 2001
From: Jonas Budelmann <jonas.budelmann@gmail.com>
Date: Thu, 24 Oct 2013 11:03:09 +1100
Subject: [PATCH] Update existing constraint rather than adding a new one. If
 one exists that is the same apart from the constant property

---
 Masonry/MASViewAttribute.m  | 13 +++++++------
 Masonry/MASViewConstraint.m | 31 ++++++++++++++++++++++++++++---
 2 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/Masonry/MASViewAttribute.m b/Masonry/MASViewAttribute.m
index f15f1bb8..86bdbfd6 100644
--- a/Masonry/MASViewAttribute.m
+++ b/Masonry/MASViewAttribute.m
@@ -21,15 +21,16 @@ - (id)initWithView:(MAS_VIEW *)view layoutAttribute:(NSLayoutAttribute)layoutAtt
 }
 
 - (BOOL)isSizeAttribute {
-    return self.layoutAttribute == NSLayoutAttributeWidth || self.layoutAttribute == NSLayoutAttributeHeight;
+    return self.layoutAttribute == NSLayoutAttributeWidth
+        || self.layoutAttribute == NSLayoutAttributeHeight;
 }
 
-- (BOOL)isEqual:(id)object {
-    if ([object isKindOfClass:self.class]) {
-        MASViewAttribute *attr = object;
-        return ([self.view isEqual:attr.view] && self.layoutAttribute == attr.layoutAttribute);
+- (BOOL)isEqual:(MASViewAttribute *)viewAttribute {
+    if ([viewAttribute isKindOfClass:self.class]) {
+        return [self.view isEqual:viewAttribute.view]
+            && self.layoutAttribute == viewAttribute.layoutAttribute;
     }
-    return [super isEqual:object];
+    return [super isEqual:viewAttribute];
 }
 
 - (NSUInteger)hash {
diff --git a/Masonry/MASViewConstraint.m b/Masonry/MASViewConstraint.m
index 4dc12c68..0d77d5af 100644
--- a/Masonry/MASViewConstraint.m
+++ b/Masonry/MASViewConstraint.m
@@ -291,15 +291,40 @@ - (void)install {
                  @"couldn't find a common superview for %@ and %@",
                  firstLayoutItem, secondLayoutItem);
         self.installedView = closestCommonSuperview;
-        [closestCommonSuperview addConstraint:layoutConstraint];
-        self.layoutConstraint = layoutConstraint;
     } else {
         self.installedView = firstLayoutItem;
-        [firstLayoutItem addConstraint:layoutConstraint];
+    }
+
+    MASLayoutConstraint *existingConstraint = [self layoutConstraintSimiliarTo:layoutConstraint];
+    if (existingConstraint) {
+        // just update the constant
+        existingConstraint.constant = layoutConstraint.constant;
+        self.layoutConstraint = existingConstraint;
+    } else {
+        [self.installedView addConstraint:layoutConstraint];
         self.layoutConstraint = layoutConstraint;
     }
 }
 
+- (MASLayoutConstraint *)layoutConstraintSimiliarTo:(MASLayoutConstraint *)layoutConstraint {
+    // check if any constraints are the same apart from the only mutable property constant
+
+    // go through constraints in reverse as we do not want to match auto-resizing or interface builder constraints
+    // and they are likely to be added first.
+    for (NSLayoutConstraint *existingConstraint in self.installedView.constraints.reverseObjectEnumerator) {
+        if (![existingConstraint isKindOfClass:MASLayoutConstraint.class]) continue;
+        if (existingConstraint.firstItem != layoutConstraint.firstItem) continue;
+        if (existingConstraint.secondItem != layoutConstraint.secondItem) continue;
+        if (existingConstraint.firstAttribute != layoutConstraint.firstAttribute) continue;
+        if (existingConstraint.secondAttribute != layoutConstraint.secondAttribute) continue;
+        if (existingConstraint.multiplier != layoutConstraint.multiplier) continue;
+        if (existingConstraint.priority != layoutConstraint.priority) continue;
+
+        return (id)existingConstraint;
+    }
+    return nil;
+}
+
 - (void)uninstall {
     [self.installedView removeConstraint:self.layoutConstraint];
     self.layoutConstraint = nil;