C#如何在打开主界面的同时打开登陆界面

这个问题是个多线程问题，如果你不是很熟悉的话，你可以在网上查哈资料
using System.Threading;//注意引用

public void RunApplication()
{
//同时调用另外一个窗体
Application.Run(new FrmSecond());
}

private void Form1_Load(object sender, EventArgs e)
{
this.WindowState = FormWindowState.Maximized;
ThreadStart start = new ThreadStart(RunApplication);
Thread xc = new Thread(start);
xc.Start();
}

public void ShowLogin(){
Form frm=new Form();
ShowDialog();
}

private void FormMain_Load(object sender, EventArgs e)
{
Thread thread = new Thread(new ThreadStart(ShowLogin));
thread.Start();
}

把你的代码加到Shown事件里，就会达到你要求了

Whikiey 正解
鉴定完毕