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

一.写在前面

按国际惯例,先来讲一讲怎么涉及到这里了.我希望一个UI模块在Awake场景加载之后就可以通过回调来响应服务器消息,但是因为这个模块在场景加载的时候并不会被激活,所以需要将事件的订阅提前到该模块被加载之前,这就让我想起来了UGUI的Button的onClick事件,既然如此那就让我们一起来发现真相把.

二.真相就在这里!

首先呢,UGUI是开源的,要看源码啊,就不得不推荐Resharper了,这个插件有一个Assembly Explorer的东西,可以看到dll中的内容.下面就是Button的源码.我们看到,Button的onClick是一个继承了UnityEvent的对象,而这个对象是被标记了"[Serializable]"的,表示这个对象可以被序列话,而根据UnityEvent,则我们的目的就达到了.

// Decompiled with JetBrains decompiler
// Type: UnityEngine.UI.Button
// Assembly: UnityEngine.UI, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
// MVID: FFDB3AB2-A87C-4B43-B613-BCF0D7807E81
// Assembly location: D:practiceTaiDouARPGLibraryUnityAssembliesUnityEngine.UI.dll

using System;
using System.Collections;
using System.Diagnostics;
using UnityEngine;
using UnityEngine.Events;
using UnityEngine.EventSystems;
using UnityEngine.Serialization;

namespace UnityEngine.UI
{
  [AddComponentMenu("UI/Button", 30)]
  public class Button : Selectable, IEventSystemHandler, IPointerClickHandler, ISubmitHandler
  {
    [SerializeField]
    [FormerlySerializedAs("onClick")]
    private Button.ButtonClickedEvent m_OnClick = new Button.ButtonClickedEvent();

    public Button.ButtonClickedEvent onClick
    {
      get
      {
        return this.m_OnClick;
      }
      set
      {
        this.m_OnClick = value;
      }
    }

    protected Button()
    {
    }

    private void Press()
    {
      if (!this.IsActive() || !this.IsInteractable())
        return;
      this.m_OnClick.Invoke();
    }

    public virtual void OnPointerClick(PointerEventData eventData)
    {
      if (eventData.button != PointerEventData.InputButton.Left)
        return;
      this.Press();
    }

    public virtual void OnSubmit(BaseEventData eventData)
    {
      this.Press();
      if (!this.IsActive() || !this.IsInteractable())
        return;
      this.DoStateTransition(Selectable.SelectionState.Pressed, false);
      this.StartCoroutine(this.OnFinishSubmit());
    }

    [DebuggerHidden]
    private IEnumerator OnFinishSubmit()
    {
      // ISSUE: object of a compiler-generated type is created
      return (IEnumerator) new Button.u003COnFinishSubmitu003Ec__Iterator1()
      {
        u003Cu003Ef__this = this
      };
    }

    [Serializable]
    public class ButtonClickedEvent : UnityEvent
    {
    }
  }
}

 三.总结

其实这篇博客还没写完,为什么可以这样搞还没弄明白,等以后更新吧.