How to enable Default Values for properties in a 'CollectionEditor' dialog

Question

Please read entire question first to understand where I would have the ability to reset the default value of a property.

When defining a custom class that can be visually designed, one can implement a collections editor to modify properties which are lists, arrays, collections, using the following pattern:

[Editor(typeof(CollectionEditor), typeof(UITypeEditor)),
    DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
public ElementCollection Elements
{
    get;
}

Editing the Elements property of this class will now launch a CollectionEditor dialog, with a list of members on the left and a PropertyGrid on the right.

The problem is, it appears that context menus are disabled for this property grid. Therefore, I cannot right click on a property to 'reset' its value to default, despite having a [DefaultValue] attribute defined.

Yet, the DefaultValue attribute is recognized, because the property is not serialized (and correctly displayed in unbolded text within the grid).

I would like to know how to enable this context menu on the PropertyGrid from the CollectionEditor dialog:

or alternatively, any way (hot key, etc.) that can be implemented to be able to reset these collection item properties.

Answer 1

You can create your own collection editor inheriting CollectionEditor class and then override CreateCollectionForm method, find property grid in the collection editor form and then register a ContextMenuStrip containing a Reset menu item for property grid, then reset the property using ResetSelectedProperty:

public class MyCollectionEditor : CollectionEditor
{
    public MyCollectionEditor() : base(typeof(Collection<MyElement>)) { }
    protected override CollectionForm CreateCollectionForm()
    {
        var form = base.CreateCollectionForm();
        var grid = form.Controls.Find("propertyBrowser", true).First() as PropertyGrid;
        var menu = new ContextMenuStrip();
        menu.Items.Add("Reset", null, (s, e) => { grid.ResetSelectedProperty(); });
        //Enable or disable Reset menu based on selected property
        menu.Opening += (s, e) =>
        {
            if (grid.SelectedGridItem != null && grid.SelectedObject != null &&
                grid.SelectedGridItem.PropertyDescriptor.CanResetValue(null))
                menu.Items[0].Enabled = true;
            else
                menu.Items[0].Enabled = false;
        };
        grid.ContextMenuStrip = menu;
        return form;
    }
}

And decorate your collection property this way:

[Editor(typeof(MyCollectionEditor), typeof(UITypeEditor))]
[DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
public Collection<MyElement> MyElements { get; private set; }

Following this approach you can simply add a separator, commands and description menus.