Configurations::Count Property

public void CodeExample(DTE2 dte, AddIn addin)
{   
    try
    {   // Make sure you have a solution loaded into Visual Studio
        // before running the following example. Make sure the "Any
        // CPU" option is marked in the Configuration Manager dialog box.
        Configurations configs = null;
        if (dte.Solution.Projects.Count > 0)
        {
            configs = dte.Solution.Projects.Item(1).ConfigurationManager.Platform("Any CPU");
            // Show the number of configurations in the collection.
            MessageBox.Show(configs.Count.ToString());
        }
    }
    catch(Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}