Adds 'constraint.isActive = bool' to Constraint (#496)

* delegate identical 'constraint creation' code to 'prepareConstraints'

* adds 'set(isActivated:)' method to call appropriate 'activate/deactivate' based on bool

cleans up about 30 lines of

    if foo { activate }
    else { deactivate }

code in my app

* instead of 'set(isActivated:)', use 'isActive = value'

Source/Constraint.swift

@@ -49,6 +49,16 @@ public final class Constraint {
     public var layoutConstraints: [LayoutConstraint]
     
     public var isActive: Bool {
+        set {
+            if newValue {
+                activate()
+            }
+            else {
+                deactivate()
+            }
+        }
+        
+        get {
             for layoutConstraint in self.layoutConstraints {
                 if layoutConstraint.isActive {
                     return true
@@ -56,6 +66,7 @@ public final class Constraint {
             }
             return false
         }
+    }
     
     // MARK: Initialization
 

Source/ConstraintMaker.swift

@@ -171,15 +171,7 @@ public class ConstraintMaker {
     }
     
     internal static func makeConstraints(item: LayoutConstraintItem, closure: (_ make: ConstraintMaker) -> Void) {
-        let maker = ConstraintMaker(item: item)
-        closure(maker)
-        var constraints: [Constraint] = []
-        for description in maker.descriptions {
-            guard let constraint = description.constraint else {
-                continue
-            }
-            constraints.append(constraint)
-        }
+        let constraints = prepareConstraints(item: item, closure: closure)
         for constraint in constraints {
             constraint.activateIfNeeded(updatingExisting: false)
         }
@@ -196,15 +188,7 @@ public class ConstraintMaker {
             return
         }
         
-        let maker = ConstraintMaker(item: item)
-        closure(maker)
-        var constraints: [Constraint] = []
-        for description in maker.descriptions {
-            guard let constraint = description.constraint else {
-                continue
-            }
-            constraints.append(constraint)
-        }
+        let constraints = prepareConstraints(item: item, closure: closure)
         for constraint in constraints {
             constraint.activateIfNeeded(updatingExisting: true)
         }

Tests/SnapKitTests/Tests.swift

@@ -264,6 +264,40 @@ class SnapKitTests: XCTestCase {
         
     }
     
+    func testSetIsActivatedConstraints() {
+        let v1 = View()
+        let v2 = View()
+        self.container.addSubview(v1)
+        self.container.addSubview(v2)
+        
+        var c1: Constraint? = nil
+        var c2: Constraint? = nil
+        
+        v1.snp.prepareConstraints { (make) -> Void in
+            c1 = make.top.equalTo(v2.snp.top).offset(50).constraint
+            c2 = make.left.equalTo(v2.snp.top).offset(50).constraint
+            return
+        }
+        
+        XCTAssertEqual(self.container.snp_constraints.count, 0, "Should have 0 constraints")
+        
+        c1?.isActive = true
+        c2?.isActive = false
+        
+        XCTAssertEqual(self.container.snp_constraints.count, 1, "Should have 1 constraint")
+        
+        c1?.isActive = true
+        c2?.isActive = true
+        
+        XCTAssertEqual(self.container.snp_constraints.count, 2, "Should have 2 constraints")
+        
+        c1?.isActive = false
+        c2?.isActive = false
+        
+        XCTAssertEqual(self.container.snp_constraints.count, 0, "Should have 0 constraints")
+        
+    }
+    
     func testEdgeConstraints() {
         let view = View()
         self.container.addSubview(view)