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.