.NET 6 WinForms自定义控件智能标签不显示的解决方法

我已实现一个自定义控件，为使其正常工作需扩展设计时支持并创建智能标签。我创建了继承自ControlDesigner的自定义Designer类、DesignerActionList，并将DesignerActionList正确添加至CustomDesigner::ActionLists，但切换到WinForms设计器时，无法看到智能标签面板。无论尝试何种方法都未成功，即使按照文档示例实现的自定义控件ColorLabel，其智能标签也无法显示。

我使用的是**.NET 6 WinForms应用程序**，严格遵循文档示例的步骤操作，可参考以下示例代码复现问题。

自定义控件及其Designer的示例代码 #

[Designer(typeof(ColorLabelDesigner))]
public class ColorLabel : Label
{
    private bool colorLockedValue = false;

    public bool ColorLocked
    {
        get
        {
            return colorLockedValue;
        }
        set
        {
            colorLockedValue = value;
        }
    }

    public override Color BackColor
    {
        get
        {
            return base.BackColor;
        }
        set
        {
            if (ColorLocked)
                return;
            else
                base.BackColor = value;
        }
    }

    public override Color ForeColor
    {
        get
        {
            return base.ForeColor;
        }
        set
        {
            if (ColorLocked)
                return;
            else
                base.ForeColor = value;
        }
    }
}

[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
public class ColorLabelDesigner :
          ControlDesigner
{
    private DesignerActionListCollection actionLists; 
    public override DesignerActionListCollection ActionLists
    {
        get
        {
            if (null == actionLists)
            {
                actionLists = new DesignerActionListCollection();
                actionLists.Add(
                    new ColorLabelActionList(this.Component));
            }
            return actionLists;
        }
    }
} 
public class ColorLabelActionList :
          System.ComponentModel.Design.DesignerActionList
{
    private ColorLabel colLabel;

    private DesignerActionUIService designerActionUISvc = null; 
    public ColorLabelActionList(IComponent component) : base(component)
    {
        this.colLabel = component as ColorLabel; 
        this.designerActionUISvc =
            GetService(typeof(DesignerActionUIService))
            as DesignerActionUIService;
    } 
    private PropertyDescriptor GetPropertyByName(String propName)
    {
        PropertyDescriptor prop;
        prop = TypeDescriptor.GetProperties(colLabel)[propName];
        if (null == prop)
            throw new ArgumentException(
                 "Matching ColorLabel property not found!",
                  propName);
        else
            return prop;
    } 
    public Color BackColor
    {
        get
        {
            return colLabel.BackColor;
        }
        set
        {
            GetPropertyByName("BackColor").SetValue(colLabel, value);
        }
    }

    public Color ForeColor
    {
        get
        {
            return colLabel.ForeColor;
        }
        set
        {
            GetPropertyByName("ForeColor").SetValue(colLabel, value);
        }
    }
     
    public bool LockColors
    {
        get
        {
            return colLabel.ColorLocked;
        }
        set
        {
            GetPropertyByName("ColorLocked").SetValue(colLabel, value); 
            this.designerActionUISvc.Refresh(this.Component);
        }
    }

    public String Text
    {
        get
        {
            return colLabel.Text;
        }
        set
        {
            GetPropertyByName("Text").SetValue(colLabel, value);
        }
    } 
    public void InvertColors()
    {
        Color currentBackColor = colLabel.BackColor;
        BackColor = Color.FromArgb(
            255 - currentBackColor.R,
            255 - currentBackColor.G,
            255 - currentBackColor.B);

        Color currentForeColor = colLabel.ForeColor;
        ForeColor = Color.FromArgb(
            255 - currentForeColor.R,
            255 - currentForeColor.G,
            255 - currentForeColor.B);
    } 
    public override DesignerActionItemCollection GetSortedActionItems()
    {
        DesignerActionItemCollection items = new DesignerActionItemCollection();

        //Define static section header entries.
        items.Add(new DesignerActionHeaderItem("Appearance"));
        items.Add(new DesignerActionHeaderItem("Information"));

        //Boolean property for locking color selections.
        items.Add(new DesignerActionPropertyItem("LockColors",
                         "Lock Colors", "Appearance",
                         "Locks the color properties."));
        if (!LockColors)
        {
            items.Add(new DesignerActionPropertyItem("BackColor",
                             "Back Color", "Appearance",
                             "Selects the background color."));
            items.Add(new DesignerActionPropertyItem("ForeColor",
                             "Fore Color", "Appearance",
                             "Selects the foreground color."));
             
            items.Add(new DesignerActionMethodItem(this,
                             "InvertColors", "Invert Colors",
                             "Appearance",
                             "Inverts the fore and background colors.",
                              true));
        }

        items.Add(new DesignerActionPropertyItem("Text",
            "Text String", "Appearance",
            "Sets the display text."));
        StringBuilder location = new StringBuilder("Location: ");
        location.Append(colLabel.Location);
        StringBuilder size = new StringBuilder("Size: ");
        size.Append(colLabel.Size);
        items.Add(new DesignerActionTextItem(location.ToString(),
                         "Information"));
        items.Add(new DesignerActionTextItem(size.ToString(),
                         "Information"));

        return items;
    }
}

核心问题 #

我的问题并非“如何创建智能标签”，而是“如何为自定义控件正确配置智能标签使其显示？”我推测缺少某些配置，但此前无设计时开发经验。

内容的提问来源于stack exchange，提问作者jtxkopt - STOP GENOCIDE