unity3d：UGUI层级设置有几种方式，最终是设置了什么

using System;
using System.Runtime.CompilerServices;
using System.Threading;
using UnityEngine.Bindings;
using UnityEngine.Scripting;

namespace UnityEngine
 {
     /// <summary>
     ///   <para>Element that can be used for screen rendering.</para>
     /// </summary>
     [NativeHeader("Runtime/UI/Canvas.h"), NativeHeader("Runtime/UI/UIStructs.h"), NativeClass("UI::Canvas"), RequireComponent(typeof(RectTransform))]
     public sealed class Canvas : Behaviour
     {
         public delegate void WillRenderCanvases();

         public static event Canvas.WillRenderCanvases willRenderCanvases
         {
             add
             {
                 Canvas.WillRenderCanvases willRenderCanvases = Canvas.willRenderCanvases;
                 Canvas.WillRenderCanvases willRenderCanvases2;
                 do
                 {
                     willRenderCanvases2 = willRenderCanvases;
                     willRenderCanvases = Interlocked.CompareExchange<Canvas.WillRenderCanvases>(ref Canvas.willRenderCanvases, (Canvas.WillRenderCanvases)Delegate.Combine(willRenderCanvases2, value), willRenderCanvases);
                 }
                 while (willRenderCanvases != willRenderCanvases2);
             }
             remove
             {
                 Canvas.WillRenderCanvases willRenderCanvases = Canvas.willRenderCanvases;
                 Canvas.WillRenderCanvases willRenderCanvases2;
                 do
                 {
                     willRenderCanvases2 = willRenderCanvases;
                     willRenderCanvases = Interlocked.CompareExchange<Canvas.WillRenderCanvases>(ref Canvas.willRenderCanvases, (Canvas.WillRenderCanvases)Delegate.Remove(willRenderCanvases2, value), willRenderCanvases);
                 }
                 while (willRenderCanvases != willRenderCanvases2);
             }
         }

         /// <summary>
         ///   <para>Is the Canvas in World or Overlay mode?</para>
         /// </summary>
         public extern RenderMode renderMode
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>Is this the root Canvas?</para>
         /// </summary>
         public extern bool isRootCanvas
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
         }

         /// <summary>
         ///   <para>Get the render rect for the Canvas.</para>
         /// </summary>
         public Rect pixelRect
         {
             get
             {
                 Rect result;
                 this.get_pixelRect_Injected(out result);
                 return result;
             }
         }

         /// <summary>
         ///   <para>Used to scale the entire canvas, while still making it fit the screen. Only applies with renderMode is Screen Space.</para>
         /// </summary>
         public extern float scaleFactor
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>The number of pixels per unit that is considered the default.</para>
         /// </summary>
         public extern float referencePixelsPerUnit
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>Allows for nested canvases to override pixelPerfect settings inherited from parent canvases.</para>
         /// </summary>
         public extern bool overridePixelPerfect
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>Force elements in the canvas to be aligned with pixels. Only applies with renderMode is Screen Space.</para>
         /// </summary>
         public extern bool pixelPerfect
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>How far away from the camera is the Canvas generated.</para>
         /// </summary>
         public extern float planeDistance
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>The render order in which the canvas is being emitted to the Scene. (Read Only)</para>
         /// </summary>
         public extern int renderOrder
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
         }

         /// <summary>
         ///   <para>Override the sorting of canvas.</para>
         /// </summary>
         public extern bool overrideSorting
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>Canvas' order within a sorting layer.</para>
         /// </summary>
         public extern int sortingOrder
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>For Overlay mode, display index on which the UI canvas will appear.</para>
         /// </summary>
         public extern int targetDisplay
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>Unique ID of the Canvas' sorting layer.</para>
         /// </summary>
         public extern int sortingLayerID
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>Cached calculated value based upon SortingLayerID.</para>
         /// </summary>
         public extern int cachedSortingLayerValue
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
         }

         /// <summary>
         ///   <para>Get or set the mask of additional shader channels to be used when creating the Canvas mesh.</para>
         /// </summary>
         public extern AdditionalCanvasShaderChannels additionalShaderChannels
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>Name of the Canvas' sorting layer.</para>
         /// </summary>
         public extern string sortingLayerName
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>Returns the Canvas closest to root, by checking through each parent and returning the last canvas found. If no other canvas is found then the canvas will return itself.</para>
         /// </summary>
         public extern Canvas rootCanvas
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
         }

         /// <summary>
         ///   <para>Camera used for sizing the Canvas when in Screen Space - Camera. Also used as the Camera that events will be sent through for a World Space [[Canvas].</para>
         /// </summary>
         [NativeProperty("Camera", false, TargetType.Function)]
         public extern Camera worldCamera
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>The normalized grid size that the canvas will split the renderable area into.</para>
         /// </summary>
         [NativeProperty("SortingBucketNormalizedSize", false, TargetType.Function)]
         public extern float normalizedSortingGridSize
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>The normalized grid size that the canvas will split the renderable area into.</para>
         /// </summary>
         [Obsolete("Setting normalizedSize via a int is not supported. Please use normalizedSortingGridSize", false), NativeProperty("SortingBucketNormalizedSize", false, TargetType.Function)]
         public extern int sortingGridNormalizedSize
         {
             [MethodImpl(MethodImplOptions.InternalCall)]
             get;
             [MethodImpl(MethodImplOptions.InternalCall)]
             set;
         }

         /// <summary>
         ///   <para>Returns the default material that can be used for rendering text elements on the Canvas.</para>
         /// </summary>
         [Obsolete("Shared default material now used for text and general UI elements, call Canvas.GetDefaultCanvasMaterial()", false), FreeFunction("UI::GetDefaultUIMaterial")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern Material GetDefaultCanvasTextMaterial();

         /// <summary>
         ///   <para>Returns the default material that can be used for rendering normal elements on the Canvas.</para>
         /// </summary>
         [FreeFunction("UI::GetDefaultUIMaterial")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern Material GetDefaultCanvasMaterial();

         /// <summary>
         ///   <para>Gets or generates the ETC1 Material.</para>
         /// </summary>
         /// <returns>
         ///   <para>The generated ETC1 Material from the Canvas.</para>
         /// </returns>
         [FreeFunction("UI::GetETC1SupportedCanvasMaterial")]
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern Material GetETC1SupportedCanvasMaterial();

         /// <summary>
         ///   <para>Force all canvases to update their content.</para>
         /// </summary>
         public static void ForceUpdateCanvases()
         {
             Canvas.SendWillRenderCanvases();
         }

         [RequiredByNativeCode]
         private static void SendWillRenderCanvases()
         {
             if (Canvas.willRenderCanvases != null)
             {
                 Canvas.willRenderCanvases();
             }
         }

         [MethodImpl(MethodImplOptions.InternalCall)]
         private extern void get_pixelRect_Injected(out Rect ret);
     }
 }