VS2013 C# Excel plugin - Message boxes and forms?

Question

I'm writing an Excel plugin in C# and some functionality doesn't seem to be working. I can't figure out what the problem is. More specifically I have a condition that checks for a file and if it's not found I want to display a form. The form is not showing up. Here's the code snippet that I'm using:

if (!File.Exists(addressFile))
{
   Form addCustomerForm = new CustomerForm(customerCode);
   addCustomerForm.Show();
}

I noticed that for Office plugins reference to windows forms isn't automatically added, so in order to use standard message boxes I added using System.Windows.Forms; to the heading, however none of the message boxes are showing up. Am I restricted to Excel MsgBox? If so, how do I call it?

Answer 1

看来是一个错误阻止我的代码输入表单/消息框代码。