你有一个主表单，其中正在加载多个聊天表单...

现在，在该主表单中，

采取页面级变量

you have a main form inside which multiple chat forms are loading...
now,in that mainform,
take page level variable

List<int> openedchats = new List<int>();  </int></int>

现在，当在计时器上打开表单时

now, when open form on timer

if (!openedchats.Contains(userId))
{ 
    openedchats.add(userId);

    frmchat c = new frmchat();
    c.Tag = userId;
    c.Parent = this;
    c.show();
}
else
{
    //nothing to do
}

以父表格添加方法......

Add method... in parent form

public void RemovefromOpenedchats(int userid)
{
     openedchats.Remove(userId);	
}

和 frmchat 形式

in form_closing 事件

and in frmchat form
in form_closing event

(MainForm)this.Parent.RemovefromOpenedchats((int)this.Tag);

快乐编码！

：）

Happy Coding!
:)

目前还不是很清楚你的意思。但只需引用表单并检查它是否不是 null 或 if（form.Visible）。您还可以在打开计时器外部的表单时取消计时器。



祝你好运！

It's not very clear what you mean exactly. But simply have a reference to the form and check it isn't null or if(form.Visible). You can also cancel the timer when opening a form outside of the timer.

Good luck!