PropertyGrid will use default editor for the properties which’s type is enum. This default editor does not allow multiple selections even the Enum has Flags attribute.

I have been prepared a new Editor for this kind of properties.

Our editor’s code is as follows;



internal class FlagsEditor : UITypeEditor
   FlagsEditorControl editor = null;
   public FlagsEditor()
   { }
   // our editor is a Drop-down editor
   public override UITypeEditorEditStyle GetEditStyle(ITypeDescriptorContext context)
      return UITypeEditorEditStyle.DropDown;
   public override object EditValue(ITypeDescriptorContext context, IServiceProvider provider, object value)
       // if value is not an enum than we can not edit it
      if  (!(value is Enum))
         throw new Exception("Value doesn't support");
      // try to figure out that is this a Flags enum or not ?
      Type enumType = value.GetType();
      object[] attributes =  enumType.GetCustomAttributes(typeof(FlagsAttribute), true);
      if (attributes.Length == 0)
         throw new Exception("Editing enum hasn't got Flags attribute");
      // check the underlying type
      Type type = Enum.GetUnderlyingType(value.GetType());
      if (type != typeof(byte) && type != typeof(sbyte)  && 
            type != typeof(short) && type != typeof(ushort) && 
           type != typeof(int)&& type != typeof(uint))
        return value;
      if (provider != null)
         // use windows forms editor service to show drop down
         IWindowsFormsEditorService edSvc = provider.GetService( 
              typeof(IWindowsFormsEditorService)) as IWindowsFormsEditorService;
         if (edSvc == null)
             return value;
         if (editor == null)
             editor = new FlagsEditorControl(this);
         // prepare list
         editor.Begin(edSvc, value);
         // show drop down now
         // now we take the result
         value = editor.Value;
         // reset editor
      return Convert.ChangeType(value, type);

In this code FlagsEditorControl is a UserControl which PropertyGrid hosts it in a drop down during the edit operation.
You can change your design by changing this Control.

To use this editor for a property, we have to write Editor Attribute to that property as the below;

// set editor of this property to our FlagsEditor
[Editor(typeof(FlagsEditor), typeof(UITypeEditor))]
public FileAttributes FlagsAttribute
       get { return _FlagsAttribute; }
       set { _FlagsAttribute = value; }