WinForms component properties at Design time

Question

I have tried to write my own component to change some control properties. The idea is that I drop this component from toolbox to the form, and in property windows in designer I can select for which control it should be used, so like this:

My code is:

public class ShapeForm : Component
{
    private int _shape;

    public ShapeForm()
    {
        Shape = 20;
    }

    [TypeConverter(typeof(ControlTypeConverter))]
    public Control TargetControl { get; set; }

    [Browsable(false)] // don't show in the property grid 
    public List<Control> Controls { get; private set; }

    public ContainerControl Target { get; set; } = null;

    public override ISite Site
    {
        get { return base.Site; }
        set
        {
            base.Site = value;

            IDesignerHost host = value?.GetService(
                typeof(IDesignerHost)) as IDesignerHost;
            IComponent componentHost = host?.RootComponent;
            if (componentHost is ContainerControl)
            {
                Target = componentHost as ContainerControl;
                Controls = new List<Control>();
                foreach (Control control in (componentHost as ContainerControl).Controls)
                {

                    Controls.Add(control);
                }
                ;

            }
        }
    }

    public class ControlTypeConverter : TypeConverter
    {
        public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
        {
            // we only know how to convert from to a string
            return typeof(Control) == destinationType;
        }

        public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value,
            Type destinationType)
        {
            if (typeof(string) == destinationType)
            {
                Control control = value as Control;
                if (control != null)
                    return control;
            }
            return "(none)";
        }
    }

    [
        Category("Shaping"),
        Description("Set corner shape radius"),
        Browsable(true)
    ]
    public int Shape
    {
        set
        {
            _shape = value;
            //SetShaping();
        }
        get { return _shape; }
    }


}'

But I get only one element and not all controls in this form like on first screenshot:

[ ]

Answer 1

Use this code;

[Browsable(true)]
[Editor(typeof(TestDesignProperty), typeof(UITypeEditor))]
[DefaultValue(null)]
public string SelectedObject { get; set; }

public class TestDesignProperty : UITypeEditor
{
    public override UITypeEditorEditStyle GetEditStyle(ITypeDescriptorContext context)
    {
        return UITypeEditorEditStyle.DropDown;
    }

    public override object EditValue(ITypeDescriptorContext context, IServiceProvider provider, object value)
    {

        var edSvc = (IWindowsFormsEditorService)provider.GetService(typeof(IWindowsFormsEditorService));
        ListBox lb = new ListBox();
        var form1 = (Form1) Activator.CreateInstance(typeof (Form1)); //Change with your form class
        foreach (Control control in form1.Controls)
        {
            lb.Items.Add(control.Name);
        }

        if (value != null)
        {
            lb.SelectedItem = value;
        }

        edSvc.DropDownControl(lb);

        value = (string)lb.SelectedItem;

        return value;
    }
}