【Unity知识点详解】Button点击事件拓展，单击、双击、长按实现

Button拓展

        今天来聊一下关于Button的事件拓展，这里只是拿Button来举例，Unity中其他的UI组件如Toggle、Slider等都也适用。

        我们知道在Button中我们可以通过onClick的方式来添加点击事件，但在游戏开发过程中我们往往对Button有着更多的功能需求，比如说双击、长按、按钮按下、按钮弹起等。这里举一个游戏中实际的例子，在游戏背包中的道具，单击道具时我们需要显示道具的tips框，双击时我们会去使用道具，长按时我们则可以拖动道具，当长按弹起时则道具回到原位或移动到新格子内。虽然这里的背包道具不是按钮，但在单个UI组件上集合了单击、双击、长按、按钮弹起等事件的响应。接下来将介绍如何拓展UI组件来实现这些功能。

        首先我们来认识一下Selectable这个类，Selectable是所有交互组件的基类，Unity原生的Button组件就是继承了Selectable，我们要拓展Button功能也是对Selectable下的OnPointerDown、OnPointerUp等接口进行重写。

        话不多说先上代码，代码有点长大家可以先跳过细节，后面慢慢讲解。

using System;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.EventSystems;


public class ExButton : Button
{
    private enum EnumExButtonState
    {
        /// <summary>空</summary>
        None,
        /// <summary>鼠标按下</summary>
        PointerDown,
        /// <summary>鼠标按下</summary>
        PointerUp,
        /// <summary>单击</summary>
        Click,
        /// <summary>双击</summary>
        DoubleClick,
        /// <summary>长按开始</summary>
        PressBegin,
        /// <summary>长按</summary>
        Press,
        /// <summary>长按结束</summary>
        PressEnd,
    }

    /// <summary>按钮状态</summary>
    private EnumExButtonState mButtonState = EnumExButtonState.None;
    /// <summary>鼠标按下时间</summary>
    private float mPointerDownTime = 0.0f;
    [SerializeField]
    /// <summary>双击间隔时间</summary>
    private float mDoubleClickInterval = 0.2f;
    [SerializeField]
    /// <summary>长按开始时间</summary>
    private float mPressBeginTime = 0.3f;
    [SerializeField]
    /// <summary>长按间隔时间，0为每帧调用</summary>
    private float mPressIntervalTime = 0.2f;
    /// <summary>长按缓存时间</summary>
    private float mPressCacheTime = 0f;

    public Action OnClick { get; set; }
    public Action OnDoubleClick { get; set; }
    public Action OnPressBegin { get; set; }
    public Action OnPress { get; set; }
    public Action OnPressEnd { get; set; }

    public override void OnPointerDown(PointerEventData eventData)
    {
        if (OnDoubleClick != null)
        {
            if (mButtonState == EnumExButtonState.None)
            {
                mButtonState = EnumExButtonState.PointerDown;
                mPointerDownTime = Time.time;
            }
            else if (mButtonState == EnumExButtonState.PointerUp)
            {
                if (Time.time - mPointerDownTime < mDoubleClickInterval)
                {
                    mButtonState = EnumExButtonState.DoubleClick;
                    return;
                }
                else
                {
                    mButtonState = EnumExButtonState.PointerDown;
                    mPointerDownTime = Time.time;
                }
            }
        }

        if (OnPressBegin != null || OnPress != null || OnPressEnd != null)
        {
            if (mButtonState != EnumExButtonState.DoubleClick)
            {
                mButtonState = EnumExButtonState.PointerDown;
                mPointerDownTime = Time.time;
            }
        }

        if (OnClick != null) { }
    }

    public override void OnPointerUp(PointerEventData eventData)
    {
        if (OnDoubleClick != null)
        {
            if (mButtonState == EnumExButtonState.DoubleClick)
                return;
        }

        if (OnPressBegin != null || OnPress != null || OnPressEnd != null)
        {
            if (mButtonState == EnumExButtonState.Press)
            {
                mButtonState = EnumExButtonState.PressEnd;
                return;
            }
        }

        if (OnClick != null)
        {
            if (mButtonState == EnumExButtonState.PointerDown)
                mButtonState = EnumExButtonState.PointerUp;
        }
    }

    private void Update()
    {
        ProcessUpdate();
        ResponseButtonState();
    }

    private void ProcessUpdate()
    {
        if (OnDoubleClick != null) { }

        if (OnPressBegin != null || OnPress != null || OnPressEnd != null)
        {
            if (mButtonState == EnumExButtonState.PointerDown)
            {
                if (Time.time - mPointerDownTime > mPressBeginTime)
                {
                    mButtonState = EnumExButtonState.PressBegin;
                    mPressCacheTime = 0f;
                    return;
                }
            }
        }

        if (OnClick != null)
        {
            if (mButtonState == EnumExButtonState.PointerUp)
            {
                if (OnDoubleClick != null)
                {
                    if (Time.time - mPointerDownTime > mDoubleClickInterval)
                        mButtonState = EnumExButtonState.Click;
                }
                else
                {
                    mButtonState = EnumExButtonState.Click;
                }
            }
        }
    }

    private void ResponseButtonState()
    {
        switch (mButtonState)
        {
            case EnumExButtonState.None:
                break;
            case EnumExButtonState.Click:
                OnClick?.Invoke();
                mButtonState = EnumExButtonState.None;
                break;
            case EnumExButtonState.DoubleClick:
                OnDoubleClick?.Invoke();
                mButtonState = EnumExButtonState.None;
                break;
            case EnumExButtonState.PressBegin:
                OnPressBegin?.Invoke();
                mButtonState = EnumExButtonState.Press;
                break;
            case EnumExButtonState.Press:
                {
                    mPressCacheTime += Time.deltaTime;
                    if (mPressCacheTime >= mPressIntervalTime)
                    {
                        mPressCacheTime = mPressCacheTime - mPressIntervalTime;
                        OnPress?.Invoke();
                    }
                    break;
                }
            case EnumExButtonState.PressEnd:
                OnPressEnd?.Invoke();
                mButtonState = EnumExButtonState.None;
                break;
            default:
                break;
        }
    }
}

        ExButton组件功能的拓展需要继承自Button类，并且重写OnPointerDown、OnPointerUp方法（这里根据需求只重写了OnPointerDown、OnPointerUp方法，大家可以根据自己的需求重写Selectable下的方法）。根据需求我们要实现点击、双击、长按、长按开始、长按结束事件的回调，所以在代码中我们提供了OnClick、OnDoubleClick、OnPressBegin、OnPress、OnPressEnd回调方法。

public Action OnClick { get; set; }
public Action OnDoubleClick { get; set; }
public Action OnPressBegin { get; set; }
public Action OnPress { get; set; }
public Action OnPressEnd { get; set; }

        逻辑采用了单状态机来实现，在OnPointerDown、OnPointerUp、Update方法中去改变成员mButtonState的状态，最终在ResponseButtonState方法中根据mButtonState的状态去进行事件的回调。

        在逻辑中也进行了事件回调的优化处理，当OnClick、OnDoubleClick、OnPressBegin、OnPress、OnPressEnd所有回调都被注册时，会优先处理OnDoubleClick，其次是OnPressBegin、OnPress、OnPressEnd，最后才是OnClick。例如当OnDoubleClick未被注册时，则会跳过OnDoubleClick对应的逻辑判断，提前处理并响应其他回调事件。

        

base.OnPointerDown、base.OnPointerUp

public override void OnPointerDown(PointerEventData eventData)
{
	base.OnPointerDown(eventData);
}

public override void OnPointerUp(PointerEventData eventData)
{
	base.OnPointerUp(eventData);
}

        在重写OnPointerDown、OnPointerUp后如需保留原有功能，需要调用base.OnPointerDown、base.OnPointerUp方法。只有调用基类方法，按钮的按下颜色改变才会有效果，当然这些基类方法也可以在别处调用。

官方文档连接

Selectable文档连接：https://docs.unity3d.com/Packages/com.unity.ugui@2.0/manual/script-Selectable.html

Selectable类API文档连接：https://docs.unity3d.com/Packages/com.unity.ugui@2.0/api/UnityEngine.UI.Selectable.html?q=selectable