 private extension ConstraintManager {
     
     func setSettedConstraint(constraint:Constraint) {
-        settedConstraints.forEach { cons in
-            if let _to = cons.to {
-                if _to == constraint.to && cons.direction == constraint.direction {
-                    //  移除重复的约束
-                    settedConstraints.remove(cons)
-                }
-            } else {
-                //  移除无效（to == nil）的约束
-                settedConstraints.remove(cons)
+        settedConstraints.forEach { con in
+            if con.to == nil || con.from == nil {
+                settedConstraints.remove(con)
+            } else if con.to == constraint.to && con.direction == constraint.direction {
+                settedConstraints.remove(con)
             }
         }
         settedConstraints.insert(constraint)

    /// 确定了该 UIView.frame 后，装载 Constraint 至 to.ruler.section 中
    // TODO: 参数可变性还是一个问题！
    func setConstraintsFrom(view: UIView) {
        assert(NSThread.isMainThread(), "This method should invoke in mainQueue!")
        constraints.forEach { constraint in
            if constraint.from == view {
                let _from = constraint.from

        
        _constraint.to = to
        _constraint.value = value
        singleton.constraints.insert(_constraint)
        singleton.holder.clearConstraintAt(direction)
        
        assert(singleton.noConstraintCirculationWith(_constraint), "\n⚠️FangYuan: There is a constraint circulation between\n\(to)\n🔄\n\(_constraint.from)\n")
    }

    class func layout(view:UIView) {
