C# VSTO Outlook Addin 分别计算收件人 .CC、.TO、.BCC答案

【问题标题】：C# VSTO Outlook Addin count recipients .CC, .TO, .BCC separatelyC# VSTO Outlook Addin 分别计算收件人 .CC、.TO、.BCC
【发布时间】：2021-03-03 13:39:01
【问题描述】：

在我的 Outlook 插件中，我需要添加创建新电子邮件的条件。 .TO 字段中只能有一个收件人。

不允许将配方添加到字段.CC、BCC。

(inspectorMailItem.Recipients.Count != 1) 的条件有效，(inspectorMailItem.Attachments.Count == 0) 的条件也有效。

但是为什么不能为(inspectorMailItem.CC.Count != 0) 做同样的事情呢？

错误Operator '!=' cannot be applied to operands of type 'method group' and 'int'

Microsoft.Office.Interop.Outlook.Application application = new 
    Microsoft.Office.Interop.Outlook.Application();
Inspector inspector = application.ActiveInspector();

        if (inspector.CurrentItem is MailItem inspectorMailItem)
        {
            String Subject = inspectorMailItem.Subject;
            String EmailAddress = inspectorMailItem.To;

            if (inspectorMailItem.Recipients.Count != 1)
            {
                MessageBox.Show("More then one recipient.");
            }

            else if (inspectorMailItem.CC.Count != 0)
            {
               MessageBox.Show("Recipient in CC not allowed.");    
            }

            else if (inspectorMailItem.Bcc.Count != 0)
            {
               MessageBox.Show("Recipient in Bcc not allowed.");    
            }

            else if (inspectorMailItem.Attachments.Count == 0)
            {
                MessageBox.Show("No attachment.");
            }
            
            else
            {
              //
            }

更新

我将count 替换为length：

Microsoft.Office.Interop.Outlook.Application application = new 
    Microsoft.Office.Interop.Outlook.Application();
Inspector inspector = application.ActiveInspector();

        if (inspector.CurrentItem is MailItem inspectorMailItem)
        {
            String Subject = inspectorMailItem.Subject;
            String EmailAddress = inspectorMailItem.To;

            if (inspectorMailItem.Recipients.Count != 1)
            {
                MessageBox.Show("More then one recipient.");
            }

            else if (inspectorMailItem.CC.Length != 0)
            {
               MessageBox.Show("Recipient in CC not allowed.");    
            }

            else if (inspectorMailItem.Bcc.Length != 0)
            {
               MessageBox.Show("Recipient in Bcc not allowed.");    
            }

            else if (inspectorMailItem.Attachments.Count == 0)
            {
                MessageBox.Show("No attachment.");
            }
            
            else
            {
              //
            }

它可以工作，但是当.To 为空白且.CC 为空白时，只有BCC 填充有此错误：Object reference not set to an instance of an object.

详细问题是这一行 else if (inspectorMailItem.CC.Length != 0)

【问题讨论】：

标签： c# vsto outlook-addin mailitem

【解决方案1】：

遍历MailItem.Recipients 集合并检查Recipient.Type 属性（olTo / olCC / olBCC）。

【讨论】：

【解决方案2】：

工作解决方案：

     Inspector inspector = Globals.ThisAddIn.Application.ActiveInspector();
     MailItem inspectorMailItem = inspector.CurrentItem as MailItem;

     String Subject = inspectorMailItem.Subject;
     String EmailAddress = inspectorMailItem.To;

     if (inspectorMailItem.Recipients.Count != 1)
     {
       MessageBox.Show("More then one recipient.");

                this.Hide();
            }

            else if ((inspectorMailItem.CC != null) || (inspectorMailItem.BCC != null))
            {
                MessageBox.Show("CC or BCC not allowed");

                this.Hide();
            }

            else if (inspectorMailItem.Attachments.Count == 0)
            {
                MessageBox.Show("Missing attachment");

                this.Hide();
            }
            else
            {
                //
            }

【讨论】：