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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