1、Button的状态

在Inspector中可见，对于button来说，不同的按钮状态呈现不同的颜色，如下图所示，共5种颜色。

①Normal
UI控件正常情况的状态
②Highlighted
高亮模式：
当射线与UI交互时，呈现为高亮模式，射线变成白色。
鼠标置于UI上方时所处的状态

③Pressed
鼠标左键长按状态
④Selected
选中状态，比如鼠标点击后，
⑤Disabled
button设置为不可点击，不可选择的状态

2、脚本中获取button的状态

2.1 分析状态获取

由于button为Selectable的子类，所以button中状态都通过Selectable中的实现进行处理。
接下来，让我们开始分析Selectable源码，并通过源码获取如何处理button的状态。

首先在Selectoable中知道状态类别，如下所示：

 protected SelectionState currentSelectionState
 {
     get
     {
         if (!IsInteractable())
             return SelectionState.Disabled;
         if (isPointerDown)
             return SelectionState.Pressed;
         if (hasSelection)
             return SelectionState.Selected;
         if (isPointerInside)
             return SelectionState.Highlighted;
         return SelectionState.Normal;
     }
 }

在Selectoable及Selectoable的子类中，可以通过currentSelectionState获取状态，但是在其他类中，无法直接调用其变量。

 // Change the button to the correct state
 private void EvaluateAndTransitionToSelectionState()
 {
     if (!IsActive() || !IsInteractable())
         return;

     DoStateTransition(currentSelectionState, false);
 }

在EvaluateAndTransitionToSelectionState()方法中，根据不同动作修改button的状态，继续向上寻找。

 public virtual void OnPointerEnter(PointerEventData eventData)
 {
     isPointerInside = true;
     EvaluateAndTransitionToSelectionState();
 }

看到上述代码是不是比较熟悉了，变量isPointerInside为ture时， currentSelectionState的值为SelectionState.Highlighted，所以通过这里可以发现，获取button的状态，直接复写OnPointerEnter方法就可以了。
在Selectoable类中，也有比较明显的注释了。

2.2 通过实现接口获取button的状态

2.2.1 鼠标点击与释放

button的状态为 Pressed
OnPointerDown ：
Do this when the mouse is clicked over the selectable object this script is attached to.
当鼠标点击到这个脚本所附加的可选择对象上时，执行此操作。

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 using UnityEngine.EventSystems;// Required when using Event data.

 public class ExampleClass : MonoBehaviour, IPointerDownHandler// required interface when using the OnPointerDown method.
  {
    //Do this when the mouse is clicked over the selectable object this script is attached to.
      public void OnPointerDown(PointerEventData eventData)
     {
         Debug.Log(this.gameObject.name + " Was Clicked.");
     }
 }

OnPointerUp ：
Do this when the mouse click on this selectable UI object is released.
当用户在点击这个可选择的用户界面（UI）对象后释放鼠标按钮时，执行这个动作。
OnPointerDown is also required to receive OnPointerUp callbacks
为了接收 OnPointerUp 回调，也需要实现 OnPointerDown。

      using UnityEngine;
      using System.Collections;
      using UnityEngine.UI;
      using UnityEngine.EventSystems;// Required when using Event data.
     
      public class ExampleClass : MonoBehaviour, IPointerUpHandler, IPointerDownHandler// These are the interfaces the OnPointerUp method requires.
     {
          //OnPointerDown is also required to receive OnPointerUp callbacks
          public void OnPointerDown(PointerEventData eventData)
          {
          }
     
       //Do this when the mouse click on this selectable UI object is released.
         public void OnPointerUp(PointerEventData eventData)
         {
              Debug.Log("The mouse click was released");
         }
     }

2.2.2 高亮模式

button的状态：Highlighted
Do this when the cursor enters the rect area of this selectable UI object.
当光标进入这个可选择的用户界面（UI）对象的矩形区域时，执行这个动作。
当用户的鼠标光标，射线（或触摸点，在触摸设备上）移动到某个可交互的UI元素中

   using UnityEngine;
   using System.Collections;
   using UnityEngine.UI;
    using UnityEngine.EventSystems;// Required when using Event data.
   
   public class ExampleClass : MonoBehaviour, IPointerEnterHandler// required interface when using the OnPointerEnter method.
    {
      //Do this when the cursor enters the rect area of this selectable UI object.
      public void OnPointerEnter(PointerEventData eventData)
       {
          Debug.Log("The cursor entered the selectable UI element.");
       }
   }

2.2.3 退出选中模式（高亮状态）

button的状态：Normal
Do this when the cursor exits the rect area of this selectable UI object.
当光标离开这个可选择的用户界面（UI）对象的矩形区域时，执行这个动作。

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 using UnityEngine.EventSystems;// Required when using Event data.

 public class ExampleClass : MonoBehaviour, IPointerExitHandler// required interface when using the OnPointerExit method.
 {
    //Do this when the cursor exits the rect area of this selectable UI object.
     public void OnPointerExit(PointerEventData eventData)
    {
          Debug.Log("The cursor exited the selectable UI element.");
     }
 }

2.2.4 选择模式selected

button的状态：Selected
Do this when the selectable UI object is selected.
当这个可选择的用户界面（UI）对象被选中时，执行这个动作
通过鼠标点击、键盘导航等方式

  using UnityEngine;
  using System.Collections;
  using UnityEngine.UI;
  using UnityEngine.EventSystems;// Required when using Event data.
  
   public class ExampleClass : MonoBehaviour, ISelectHandler// required interface when using the OnSelect method.
   {
       //Do this when the selectable UI object is selected.
       public void OnSelect(BaseEventData eventData)
       {
          Debug.Log(this.gameObject.name + " was selected");
       }
  }

2.2.5 退出选择模式

button状态：Normal

   using UnityEngine;
   using System.Collections;
   using UnityEngine.UI;
   using UnityEngine.EventSystems;// Required when using Event data.
  
   public class ExampleClass : MonoBehaviour, IDeselectHandler This Interface is required to receive OnDeselect callbacks.
  {
      public void OnDeselect(BaseEventData data)
      {
          Debug.Log("Deselected");
      }
  }

3、射线与UI交互设置

3.1 Canvas中组件设置

Graphic Raycaster组件为鼠标等物理输入进行处理，
Tracked Device Graphic Raycaster组件为射线交互的组件，如果Canvas中没有该组件，射线无法与该UI进行交互，当射线与UI进行交互时，射线会由红色变为白色。

3.2 EventSystem中组件设置

对于EventSystem中的设置，想要射线能够与UI之间进行交互，在Inspector中需要将组件Standalone Input Module进行移除，并添加组件XR UI Input Module，两者同时进行处理，才能实现射线与UI之间进行交互。

移除EventSystem中的Standalone Input Module中的组件
如果不移除上述组件的话，对于射线的交互效果可能出现问题
添加组件XR UI Input Module