Added support for updateConstraints

Snappy/Constraint.swift

@@ -303,7 +303,7 @@ public class Constraint {
     
     // MARK: internal
     
-    internal func install() -> Array<LayoutConstraint> {
+    internal func install(updateExisting: Bool = false) -> Array<LayoutConstraint> {
         if self.installedOnView != nil {
             NSException(name: "Cannot Install Constraint", reason: "Already installed", userInfo: nil).raise()
             return []
@@ -367,6 +367,42 @@ public class Constraint {
             layoutConstraints.append(layoutConstraint)
         }
         
+        // special logic for updating
+        if updateExisting {
+            // get existing constraints for this view
+            let existingLayoutConstraints = reverse(layoutFrom!.snp_installedLayoutConstraints)
+            
+            // array that will contain only new layout constraints
+            var newLayoutConstraints = Array<LayoutConstraint>()
+            
+            // begin looping
+            for layoutConstraint in layoutConstraints {
+                // layout constraint that should be updated
+                var updateLayoutConstraint: LayoutConstraint? = nil
+                
+                // loop through existing and check for match
+                for existingLayoutConstraint in existingLayoutConstraints {
+                    if existingLayoutConstraint == layoutConstraint {
+                        updateLayoutConstraint = existingLayoutConstraint
+                        break
+                    }
+                }
+                
+                // if we have existing one lets just update the constant
+                if updateLayoutConstraint != nil {
+                    updateLayoutConstraint!.constant = layoutConstraint.constant
+                }
+                // otherwise add this layout constraint to new list
+                else {
+                    newLayoutConstraints.append(layoutConstraint)
+                }
+            }
+            
+            // set constraints to only new ones
+            layoutConstraints = newLayoutConstraints
+        }
+        
+        // add constarints
         installOnView!.addConstraints(layoutConstraints)
         
         self.installedOnView = installOnView

Snappy/ConstraintMaker.swift

@@ -100,6 +100,23 @@ public class ConstraintMaker {
         view.snp_installedLayoutConstraints = layoutConstraints
     }
     
+    internal class func updateConstraints(view: View, block: (make: ConstraintMaker) -> ()) {
+        #if os(iOS)
+        view.setTranslatesAutoresizingMaskIntoConstraints(false)
+        #else
+        view.translatesAutoresizingMaskIntoConstraints = false
+        #endif
+        let maker = ConstraintMaker(view: view)
+        block(make: maker)
+        
+        var layoutConstraints = view.snp_installedLayoutConstraints
+        for constraint in maker.constraints {
+            layoutConstraints += constraint.install(updateExisting: true)
+        }
+        
+        view.snp_installedLayoutConstraints = layoutConstraints
+    }
+    
     internal class func removeConstraints(view: View) {
         for existingLayoutConstraint in view.snp_installedLayoutConstraints {
             existingLayoutConstraint.constraint?.uninstall()

Snappy/LayoutConstraint.swift

@@ -32,4 +32,29 @@ import AppKit
 */
 public class LayoutConstraint: NSLayoutConstraint {
     internal var constraint: Constraint?
+}
+
+public func ==(left: LayoutConstraint, right: LayoutConstraint) -> Bool {
+    if left.firstItem !== right.firstItem {
+        return false
+    }
+    if left.secondItem !== right.secondItem {
+        return false
+    }
+    if left.firstAttribute != right.firstAttribute {
+        return false
+    }
+    if left.secondAttribute != right.secondAttribute {
+        return false
+    }
+    if left.relation != right.relation {
+        return false
+    }
+    if left.priority != right.priority {
+        return false
+    }
+    if left.multiplier != right.multiplier {
+        return false
+    }
+    return true
 }