VSTO：使用变量访问CommandBarButton会产生无效引用-HRESULT的异常：0x800A01A8

Question

I am trying to add a custom button to one of Word's CommandBar 's, and then later change them to be visible or invisible. As prescribed in some tutorials that I have seen, I make sure to store the button in a class variable so my item isn't de-allocated upon garbage collection. I know the correct way to access the item later, as stated in the tutorial above, but what is wrong with the way I try below in the right click handler:

public partial class ThisAddIn
{
    private Office.CommandBar textContextMenu;
    private Office.CommandBarButton exampleMenuItem;

    private void ThisAddIn_Startup(object sender, System.EventArgs e)
    {
        // keep track of the menu for later
        textContextMenu = this.Application.CommandBars["Text"];
        // add a right click handler
        this.Application.WindowBeforeRightClick += new Word.ApplicationEvents4_WindowBeforeRightClickEventHandler(application_WindowBeforeRightClick);

        AddToToolbar();
    }

    private void AddToToolbar()
    {
        // Add a button to the command bar
        exampleMenuItem = (Office.CommandBarButton)textContextMenu.Controls.Add(
            Office.MsoControlType.msoControlButton,
            missing,
            missing,
            1,
            true);

        exampleMenuItem.Caption = "Test Button";
        exampleMenuItem.Tag = "testButton";
    }

    public void application_WindowBeforeRightClick(Word.Selection selection, ref bool Cancel)
    {
        // attempting to access the variable here throws the COM exception
        exampleMenuItem.Visible = false;
        // ... but, as in the tutorial, I can access the button like this:
        var exampleButton = (Office.CommandBarButton)textContextMenu.FindControl(
            buttonType, 
            missing, 
            "testButton");
        exampleButton.Visible = false;
    }
}

I've looked up the VBA exception 0x800A01A8 - as far as I know, I'm not trying to access a COM object that doesn't exist, but what am I missing? Why can't I access the button from a variable after it has been added in this way?

Thanks for any feedback.

Answer 1

Command bars were deprecated, you need to use the Fluent UI controls instead. What Word version do you have installed on the PC?

See Customizing Context Menus in Office 2010 for more information.