CocosCreator中，单指触屏输入

关注单指输入：按下、滑动、抬起时，传出手指位置（在UI坐标系中）。
SingleTouchCtr.ts

import { _decorator, Component, Node, input, Input, EventTouch, EventTarget } from 'cc';
const { ccclass, property } = _decorator;

export class SingleTouchCtr
{
    private _touchId: number;
    private static readonly defaultTouchId = -1;

    private _eventTarget: EventTarget;
    public get eventTarget(): EventTarget { return this._eventTarget };

    public static readonly SingleTouchDownEvent: string = 'SingleTouchDownEvent';
    public static readonly SingleTouchMoveEvent: string = 'SingleTouchMoveEvent';
    public static readonly SingleTouchUpEvent: string = 'SingleTouchUpEvent';

    public constructor()
    {
        input.on(Input.EventType.TOUCH_START, this.onTouchStart, this);
        input.on(Input.EventType.TOUCH_MOVE, this.onTouchMove, this);
        input.on(Input.EventType.TOUCH_END, this.onTouchEnd, this);
        this.resetTouchId();
        this._eventTarget = new EventTarget();
    }

    public myDestroy(): void
    {
        input.off(Input.EventType.TOUCH_START, this.onTouchStart, this);
        input.off(Input.EventType.TOUCH_MOVE, this.onTouchMove, this);
        input.off(Input.EventType.TOUCH_END, this.onTouchEnd, this);
        this._eventTarget = null;
    }

    private resetTouchId(): void
    {
        this._touchId = SingleTouchCtr.defaultTouchId;
    }
    private hasTouchId(): boolean {
        return this._touchId != SingleTouchCtr.defaultTouchId;
    }

    private onTouchStart(event: EventTouch): void
    {
        if (!this.hasTouchId()) {
            this._touchId = event.touch.getID();
            this.eventTarget.emit(SingleTouchCtr.SingleTouchDownEvent, event.touch.getUILocation());
        }
    }
    private onTouchMove(event: EventTouch): void
    {
        if (this._touchId == event.touch.getID()) {
            this.eventTarget.emit(SingleTouchCtr.SingleTouchMoveEvent, event.touch.getUILocation());
        }
    }
    private onTouchEnd(event: EventTouch): void
    {
        if (this._touchId == event.touch.getID()) {
            this.eventTarget.emit(SingleTouchCtr.SingleTouchUpEvent, event.touch.getUILocation());
            this.resetTouchId();
        }
    }
}