（12） Interactive component selectable

1. Preface

Just briefly unity Interactive components of Selectable, This component is the base class for all component interactions , That is, it realizes the mouse hover、 Click on 、 The state of departure and other events . yes button、toggle、slider And so on , Relatively simple .

2. Realization

It's easier to implement , That is, simply inherit some event interfaces （ Such as IPointerDownHandler）, Then get the event , Deal with different logic according to events . This component looks more complex （1000+ Lines of code ）, To deal with some special situations , The more complex functions are the following two ：
1、Transition The choice of , That is, different forms of expression are selected according to their different values .
2、 Receive the father CanvasGroup Control of . This function is inherited UIBehavior Get listening , Then do logical processing , such as CanvasGroup How to deal with the replacement ：

        protected override void OnCanvasGroupChanged()
        {
    
            // Figure out if parent groups allow interaction
            // If no interaction is alowed... then we need
            // to not do that :)
            var groupAllowInteraction = true;
            Transform t = transform;
            while (t != null)
            {
    
                t.GetComponents(m_CanvasGroupCache);
                bool shouldBreak = false;
                for (var i = 0; i < m_CanvasGroupCache.Count; i++)
                {
    
                    // if the parent group does not allow interaction
                    // we need to break
                    if (!m_CanvasGroupCache[i].interactable)
                    {
    
                        groupAllowInteraction = false;
                        shouldBreak = true;
                    }
                    // if this is a 'fresh' group, then break
                    // as we should not consider parents
                    if (m_CanvasGroupCache[i].ignoreParentGroups)
                        shouldBreak = true;
                }
                if (shouldBreak)
                    break;

                t = t.parent;
            }

            if (groupAllowInteraction != m_GroupsAllowInteraction)
            {
    
                m_GroupsAllowInteraction = groupAllowInteraction;
                OnSetProperty();
            }
        }

3. Last

This class is simple , If we define components by ourselves, we can simply inherit relevant interfaces to implement our own logic ,unity Of selectable Also to achieve “unity type ” Of ui And definition .