Question

I’m tweaking a WinForms application. This application has a Form that contains a PropertyGrid. An object is assigned to the SelectedObject property so that the property grid displays the properties for the object.

The type of the object assigned has a property that carries an EditorAttribute specifying a UITypeEditor.

This implementation of UITypeEditor returns UITypeEditorEditStyle.Drop in its override of GetEditStyle method. Its EditValue method displays a ListBox from which a value for the instance property can be assigned.

All well an good so far.

Now I have an additional requirement which calls for the available items in the list to be modified based on other state held by the Form hosting the PropertyGrid. I can’t work out how to get this contextual information to the EditValue method.

There doesn’t seem to be anything on the context parameter even if I try casting it to more specific types. Neither can I work out how to add some other Service to retrieve from the provider.

Any ideas?

Answer 1

I wonder if what you are trying to do would would better as a TypeConverter via GetStandardValues? But either way, both context.Instance and context.PropertyDescriptor seem to be populated in a quick test (for both GetEditStyle and EditValue):

using System;
using System.ComponentModel;
using System.Drawing.Design;
using System.Windows.Forms;
class MyData
{
    [Editor(typeof(MyEditor), typeof(UITypeEditor))]
    public string Bar { get; set; }

    public string[] Options { get; set; }
}
class MyEditor : UITypeEditor
{
    public override UITypeEditorEditStyle GetEditStyle(ITypeDescriptorContext context)
    {
        // break point here; inspect context
        return UITypeEditorEditStyle.DropDown;
    }
    public override object EditValue(ITypeDescriptorContext context, IServiceProvider provider, object value)
    {
        // break point here; inspect context
        return base.EditValue(context, provider, value);
    }

}
class Program
{
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.Run(new Form
        {
            Controls =
            {
                new PropertyGrid {
                    Dock = DockStyle.Fill,
                    SelectedObject = new MyData()
                }
            }
        });
    }
}

Or as a type-converter:

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

class MyData
{
    [TypeConverter(typeof(MyConverter))]
    public string Bar { get; set; }

    public string[] Options { get; set; }
}
class MyConverter : StringConverter
{
    public override bool GetStandardValuesSupported(ITypeDescriptorContext context)
    {
        return true;
    }
    public override StandardValuesCollection GetStandardValues(ITypeDescriptorContext context)
    {
        MyData data = (MyData)context.Instance;
        if(data == null || data.Options == null) {
            return new StandardValuesCollection(new string[0]);
        }
        return new StandardValuesCollection(data.Options);
    }
}
class Program
{
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.Run(new Form
        {
            Controls =
            {
                new PropertyGrid {
                    Dock = DockStyle.Fill,
                    SelectedObject = new MyData()
                }
            }
        });
    }
}