User Control as container at design time

Question

I'm designing a simple expander control.

I've derived from UserControl, drawn inner controls, built, run; all ok.

Since an inner Control is a Panel, I'd like to use it as container at design time. Indeed I've used the attributes:

[Designer(typeof(ExpanderControlDesigner))]
[Designer("System.Windows.Forms.Design.ParentControlDesigner, System.Design", typeof(IDesigner))] 

Great I say. But it isn't...

The result is that I can use it as container at design time but:

• The added controls go back the inner controls already embedded in the user control
• Even if I push to top a control added at design time, at runtime it is back again on controls embedded to the user control
• I cannot restrict the container area at design time into a Panel area

What am I missing? Here is the code for completeness... why this snippet of code is not working?

[Designer(typeof(ExpanderControlDesigner))]
[Designer("System.Windows.Forms.Design.ParentControlDesigner, System.Design", typeof(IDesigner))] 
public partial class ExpanderControl : UserControl
{
    public ExpanderControl()
    {
        InitializeComponent();
....

[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")] 
internal class ExpanderControlDesigner : ControlDesigner
{
    private ExpanderControl MyControl;

    public override void Initialize(IComponent component)
    {
        base.Initialize(component);

        MyControl = (ExpanderControl)component;

        // Hook up events
        ISelectionService s = (ISelectionService)GetService(typeof(ISelectionService));
        IComponentChangeService c = (IComponentChangeService)GetService(typeof(IComponentChangeService));

        s.SelectionChanged += new EventHandler(OnSelectionChanged);
        c.ComponentRemoving += new ComponentEventHandler(OnComponentRemoving);
    }

    private void OnSelectionChanged(object sender, System.EventArgs e)
    {

    }

    private void OnComponentRemoving(object sender, ComponentEventArgs e)
    {

    }

    protected override void Dispose(bool disposing)
    {
        ISelectionService s = (ISelectionService)GetService(typeof(ISelectionService));
        IComponentChangeService c = (IComponentChangeService)GetService(typeof(IComponentChangeService));

        // Unhook events
        s.SelectionChanged -= new EventHandler(OnSelectionChanged);
        c.ComponentRemoving -= new ComponentEventHandler(OnComponentRemoving);

        base.Dispose(disposing);
    }

    public override System.ComponentModel.Design.DesignerVerbCollection Verbs
    {
        get
        {
            DesignerVerbCollection v = new DesignerVerbCollection();

            v.Add(new DesignerVerb("&asd", new EventHandler(null)));

            return v;
        }
    }
}

I've found many resources (Interaction, designed, limited area), but nothing was usefull for being operative...

Actually there is a trick, since System.Windows.Forms classes can be designed (as usual) and have a correct behavior at runtime (TabControl, for example).

Answer 1

ParentControlDesigner doesn't know what you want do. It only knows you want your UserControl to be a container.

What you need to do is implement your own designer which enables design mode on the panel:

    using System.ComponentModel;
    using System.Windows.Forms;
    using System.Windows.Forms.Design;

    namespace MyCtrlLib
    {
        // specify my custom designer
        [Designer(typeof(MyCtrlLib.UserControlDesigner))]
        public partial class UserControl1 : UserControl
        {
            public UserControl1()
            {
                InitializeComponent();
            }

            // define a property called "DropZone"
            [Category("Appearance")]
            [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)] 
            public Panel DropZone
            {
                get { return panel1; }
            }
        }

        // my designer
        public class UserControlDesigner  : ParentControlDesigner
        {
            public override void Initialize(System.ComponentModel.IComponent component)
            {
                base.Initialize(component);

                if (this.Control is UserControl1)
                {
                    this.EnableDesignMode((
                       (UserControl1)this.Control).DropZone, "DropZone");
                }
            }
        }
    }

I learned this from Henry Minute on CodeProject. See the link for some improvements on the technique.