UnityEngine.UI.GraphicRegistry.RegisterGraphicForCanvas C# (CSharp) Method

        public static void RegisterGraphicForCanvas(Canvas c, Graphic graphic)
        {
            if (c != null)
            {
                IndexedSet<Graphic> set;
                instance.m_Graphics.TryGetValue(c, out set);
                if (set != null)
                {
                    set.AddUnique(graphic);
                }
                else
                {
                    set = new IndexedSet<Graphic> {
                        graphic
                    };
                    instance.m_Graphics.Add(c, set);
                }
            }
        }

        /// <summary>
        /// 17/6 2020 Graphic学习
        /// 主要是Canvas显示隐藏或者canvas控件OnEnable、Disable的时候调用
        /// 主要是检测Canvas控件的
        /// </summary>
        protected override void OnCanvasHierarchyChanged()
        {
            // Debug.Log("OnCanvasHierarchyChanged");
            // Use m_Cavas so we dont auto call CacheCanvas
            Canvas currentCanvas = m_Canvas;

            // Clear the cached canvas. Will be fetched below if active.
            m_Canvas = null;

            if (!IsActive())
            {
                return;
            }

            CacheCanvas();

            if (currentCanvas != m_Canvas)
            {
                //currentCanvas ！= m_Canvas时，说明UI更换了canvas，需要与之前的Canvas解除关联
                GraphicRegistry.UnregisterGraphicForCanvas(currentCanvas, this);

                // Only register if we are active and enabled as OnCanvasHierarchyChanged can get called
                // during object destruction and we dont want to register ourself and then become null.
                if (IsActive())
                {
                    //如果当前组件还是在激活状态下的话，就将当前UI和新的canvas进行注册绑定
                    GraphicRegistry.RegisterGraphicForCanvas(canvas, this);
                }
            }
        }