Why does onDemand setting remove my buttons from my menu?

Question

When I set the onDemand="false" attribute, my buttons disappear from my menu!

I'm setting the attribute to false so that I control its behaviour using the OnUpdate override in code. Am I doing anything wrong?

<ArcMap>
  <Commands>
    <Button id="SayHi_Btn" onDemand="false" class="SayHiButton" caption="Say Hi!" image="Images\SayHi_Btn.png" />
    <Button id="SayHello_Btn" onDemand="false" class="SayHelloButton" caption="Say Hello!" image="Images\SayHello_Btn.png" />
    <Button id="SayAloha_Btn" onDemand="false" class="SayAlohaButton" caption="Say Aloha!" image="Images\SayAloha_Btn.png" />
  </Commands>
  <Menus>
    <Menu id="ChooseGreeting_RootMenu" caption="Choose Greeting" isRootMenu="true">
      <Items>
        <Button refID="SayHello_Btn" separator="true" />
        <Button refID="SayAloha_Btn"  />
        <Button refID="SayHi_Btn" />
      </Items>
    </Menu>
  </Menus>
</ArcMap>

Answer 1

Just found that if there are any uncaught exceptions being thrown inside the OnUpdate, then the buttons disappear from the menu items.

Best to implement robust exception management inside the OnUpdate method to prevent unexpected behaviour by the buttons.

using ESRI.ArcGIS.Desktop.AddIns;

namespace ArcMapAddIn
{
    public class MyCustomButton : Button
    {
        private readonly MyExtension _myExtension;

        public MyCustomButton()
        {
            _myExtension = AddIn.FromID(ThisAddIn.IDs.MyExtension);

            Enabled = false;
        }

        protected override void OnClick()
        {
            new MessageBox.Show("My Custom Button clicked!");
        }

        protected override void OnUpdate()
        {
            Enabled = _myExtension.CanShowCustomMessage;
            // if uncaught excpetion is thrown here- this button gets removed from menu item
        }
    }
}