如何修复Unity资产方法被标记为替代，但是没有合适的方法

Question

我下载了资产存储库中的该资产，在必须将其下载到我的项目中之后，我遇到了两个错误：

  

@ 1.9.11 / Editor / Sources / UI / Common / PopupField.cs（8,36）：错误CS0246：找不到类型或名称空间名称“ BaseTextElement”。您是否缺少装配参考？

     

PopupField.cs（118,33）：错误CS0115：“ UnityEditor.PackageManager.UI.PopupField.ExecuteDefaultAction（UnityEngine.Experimental.UIElements.EventBase）”被标记为替代，但是找不到合适的替代方法

我尝试在线查找解决方案，甚至检查了此网站，但没有发现任何帮助。

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Experimental.UIElements;

namespace UnityEditor.PackageManager.UI
{
    internal class PopupField<T> : BaseTextElement, INotifyValueChanged<T>
    {
        private readonly List<T> m_PossibleValues;
        private Func<T, string> m_Callback;
        private EventCallback<ChangeEvent<T>> m_valueCallback;

        private T m_Value;

        public T value
        {
            get { return m_Value; }
            set
            {
                if (EqualityComparer<T>.Default.Equals(m_Value, value))
                    return;

                if (!m_PossibleValues.Contains(value))
                    throw new ArgumentException(string.Format("Value {0} is not present in the list of possible values", value));

                m_Value = value;
                m_Index = m_PossibleValues.IndexOf(m_Value);

                if (m_Callback != null)
                    text = m_Callback(m_Value);
                else
                    text = m_Value.ToString();

                #if UNITY_2018_3_OR_NEWER
                MarkDirtyRepaint();
                #else
                Dirty(ChangeType.Repaint);
                #endif
           }
        }

        private int m_Index = -1;

        public int index
        {
            get { return m_Index; }
            set
            {
               if (value != m_Index)
               {
                    if (value >= m_PossibleValues.Count || value < 0)
                    throw new ArgumentException(string.Format("Index {0} 
            is beyond the scope of possible value", value));
                m_Index = value;
                this.value = m_PossibleValues[m_Index];
            }
        }
        }

    /// <summary>
    /// Callback that will return the string to be set in the field's 
         label.
    /// </summary>
    /// <param name="callback"></param>
    public void SetLabelCallback(Func<T, string> callback)
    {
        m_Callback = callback;
    }

    private PopupField(List<T> possibleValues)
    {
        if (possibleValues == null)
            throw new ArgumentNullException("possibleValues can't be 
      null");

        m_PossibleValues = possibleValues;

        AddToClassList("popupField");
    }

    public PopupField(List<T> possibleValues, T defaultValue) :
        this(possibleValues)
    {
        if (defaultValue == null)
            throw new ArgumentNullException("defaultValue can't be 
      null");

        if (!m_PossibleValues.Contains(defaultValue))
            throw new ArgumentException(string.Format("Default value {0} 
      is not present in the list of possible values", defaultValue));

        // note: idx will be set when setting value
        value = defaultValue;
    }

    public PopupField(List<T> possibleValues, int defaultIndex) :
        this(possibleValues)
      {
        if (defaultIndex >= m_PossibleValues.Count || defaultIndex < 0)
            throw new ArgumentException(string.Format("Default Index {0} 
         is beyond the scope of possible value", value));

        // note: value will be set when setting idx
        index = defaultIndex;
     }

    public void SetValueAndNotify(T newValue)
    {
        if (!EqualityComparer<T>.Default.Equals(newValue, value))
        {
            using (ChangeEvent<T> evt = ChangeEvent<T>.GetPooled(value, 
       newValue))
            {
                value = newValue;
                if (m_valueCallback != null)
                    m_valueCallback(evt);
            }
        }
    }

    public void OnValueChanged(EventCallback<ChangeEvent<T>> callback)
    {
        m_valueCallback = callback;
        RegisterCallback(callback);
    }

    protected override void ExecuteDefaultAction(EventBase evt)
    {
        base.ExecuteDefaultAction(evt);

        if (evt.GetEventTypeId() == MouseDownEvent.TypeId())
            OnMouseDown();
    }

    private void OnMouseDown()
    {
        var menu = new GenericMenu();

        foreach (T item in m_PossibleValues)
        {
            bool isSelected = EqualityComparer<T>.Default.Equals(item, 
         value);
            menu.AddItem(new GUIContent(item.ToString()), isSelected,
                () => ChangeValueFromMenu(item));
        }

        var menuPosition = new Vector2(0.0f, layout.height);
        menuPosition = this.LocalToWorld(menuPosition);
        var menuRect = new Rect(menuPosition, Vector2.zero);
        menu.DropDown(menuRect);
    }

    private void ChangeValueFromMenu(T menuItem)
    {
        SetValueAndNotify(menuItem);
     }
  }
   }`