[UGUI]你说UnityEngine.UI.Button是怎么通过拖动来增加OnClick的监听器的呢?

 1 // Decompiled with JetBrains decompiler
 2 // Type: UnityEngine.UI.Button
 3 // Assembly: UnityEngine.UI, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
 4 // MVID: FFDB3AB2-A87C-4B43-B613-BCF0D7807E81
 5 // Assembly location: D:\practice\TaiDouARPG\Library\UnityAssemblies\UnityEngine.UI.dll
 6 
 7 using System;
 8 using System.Collections;
 9 using System.Diagnostics;
10 using UnityEngine;
11 using UnityEngine.Events;
12 using UnityEngine.EventSystems;
13 using UnityEngine.Serialization;
14 
15 namespace UnityEngine.UI
16 {
17   [AddComponentMenu("UI/Button", 30)]
18   public class Button : Selectable, IEventSystemHandler, IPointerClickHandler, ISubmitHandler
19   {
20     [SerializeField]
21     [FormerlySerializedAs("onClick")]
22     private Button.ButtonClickedEvent m_OnClick = new Button.ButtonClickedEvent();
23 
24     public Button.ButtonClickedEvent onClick
25     {
26       get
27       {
28         return this.m_OnClick;
29       }
30       set
31       {
32         this.m_OnClick = value;
33       }
34     }
35 
36     protected Button()
37     {
38     }
39 
40     private void Press()
41     {
42       if (!this.IsActive() || !this.IsInteractable())
43         return;
44       this.m_OnClick.Invoke();
45     }
46 
47     public virtual void OnPointerClick(PointerEventData eventData)
48     {
49       if (eventData.button != PointerEventData.InputButton.Left)
50         return;
51       this.Press();
52     }
53 
54     public virtual void OnSubmit(BaseEventData eventData)
55     {
56       this.Press();
57       if (!this.IsActive() || !this.IsInteractable())
58         return;
59       this.DoStateTransition(Selectable.SelectionState.Pressed, false);
60       this.StartCoroutine(this.OnFinishSubmit());
61     }
62 
63     [DebuggerHidden]
64     private IEnumerator OnFinishSubmit()
65     {
66       // ISSUE: object of a compiler-generated type is created
67       return (IEnumerator) new Button.\u003COnFinishSubmit\u003Ec__Iterator1()
68       {
69         \u003C\u003Ef__this = this
70       };
71     }
72 
73     [Serializable]
74     public class ButtonClickedEvent : UnityEvent
75     {
76     }
77   }
78 }