Outlook C# VSTO插件：如何拦截「建议新时间」按钮点击事件？

Outlook对象模型并没有直接暴露「建议新时间」按钮的原生点击事件，但可以通过以下两种方案实现拦截并执行自定义操作：

方案一：自定义Ribbon替换原生按钮（推荐） #

这是符合Outlook插件开发规范的稳定方案，通过VSTO的Ribbon自定义功能替换原生按钮，绑定自己的事件逻辑：

1. 添加Ribbon（XML）项：在VSTO项目中添加「Ribbon (XML)」类型的项（而非可视化设计器的Ribbon），XML方式支持精准替换内置控件。
2. 匹配原生按钮ID：「建议新时间」按钮的内置控件ID为MeetingRequestSuggestNewTime，在Ribbon XML中通过replaceId属性替换它：

<customUI xmlns="http://schemas.microsoft.com/office/2006/01/customui">
  <ribbon>
    <tabs>
      <tab idMso="TabMeetingRequest">
        <group idMso="GroupMeetingResponse">
          <button id="CustomSuggestNewTime" 
                  replaceId="MeetingRequestSuggestNewTime"
                  label="建议新时间"
                  onAction="OnCustomSuggestNewTimeClicked"/>
        </group>
      </tab>
    </tabs>
  </ribbon>
</customUI>

3. 实现点击事件逻辑：在Ribbon的后台代码中编写OnCustomSuggestNewTimeClicked方法：

public void OnCustomSuggestNewTimeClicked(Office.IRibbonControl control)
{
    // 执行你的自定义操作
    MessageBox.Show("自定义建议新时间逻辑触发");
    
    // 若需保留原生功能，可调用Outlook对象模型打开原生窗口
    Outlook.MeetingItem meetingItem = control.Context as Outlook.MeetingItem;
    if (meetingItem != null)
    {
        // 调用原生建议新时间命令
        control.Context.Application.ActiveInspector().CommandBars.ExecuteMso("MeetingRequestSuggestNewTime");
    }
}

方案二：Windows全局钩子监听按钮点击 #

如果不想替换原生按钮，可通过Windows低级鼠标钩子监听全局点击事件，判断是否点击了目标按钮：

1. 定义钩子相关API：在C#中引入Windows API函数：

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr SetWindowsHookEx(int idHook, LowLevelMouseProc lpfn, IntPtr hMod, uint dwThreadId);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern bool UnhookWindowsHookEx(IntPtr hhk);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr GetModuleHandle(string lpModuleName);

[DllImport("user32.dll")]
private static extern IntPtr WindowFromPoint(System.Drawing.Point point);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern int GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount);

private delegate IntPtr LowLevelMouseProc(int nCode, IntPtr wParam, IntPtr lParam);

private const int WH_MOUSE_LL = 14;
private const int WM_LBUTTONDOWN = 0x0201;

private LowLevelMouseProc _proc = HookCallback;
private IntPtr _hookID = IntPtr.Zero;

2. 设置钩子与回调逻辑：

public void SetHook()
{
    using (Process curProcess = Process.GetCurrentProcess())
    using (ProcessModule curModule = curProcess.MainModule)
    {
        _hookID = SetWindowsHookEx(WH_MOUSE_LL, _proc, GetModuleHandle(curModule.ModuleName), 0);
    }
}

private IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
{
    if (nCode >= 0 && wParam == (IntPtr)WM_LBUTTONDOWN)
    {
        IntPtr hwnd = WindowFromPoint(Cursor.Position);
        StringBuilder className = new StringBuilder(256);
        GetClassName(hwnd, className, className.Capacity);
        
        StringBuilder btnText = new StringBuilder(256);
        GetWindowText(hwnd, btnText, btnText.Capacity);
        
        // 判断是否是Outlook会议窗口的「建议新时间」按钮（需根据Outlook版本调整类名匹配规则）
        if (className.ToString().Contains("Outlook") && btnText.ToString().Equals("建议新时间"))
        {
            // 执行自定义操作
            MessageBox.Show("拦截到原生建议新时间按钮点击");
            
            // 若需阻止原生事件，返回非0值；否则调用CallNextHookEx继续传递消息
            // return (IntPtr)1;
        }
    }
    return CallNextHookEx(_hookID, nCode, wParam, lParam);
}

// 插件卸载时释放钩子
private void ThisAddIn_Shutdown(object sender, EventArgs e)
{
    UnhookWindowsHookEx(_hookID);
}

注意：钩子方案需适配不同Outlook版本的控件类名差异，稳定性不如自定义Ribbon，且可能被安全软件拦截，仅在无法替换原生按钮时使用。

内容的提问来源于stack exchange，提问作者Gadzhik