c# 隐藏已打开的窗口，打开登陆窗口
FormCollection fc = Application.OpenForms;//获得已打开的窗口
//循环隐藏
if (fc != null && fc.Count > 0)
{
foreach (Form window in fc)
{
window.Hide();
}
}
//清空保存的用户信息
CacheHelper.CurUserName = "";
CacheHelper.CurUserRole = -1;
//打开登陆窗口
frmLogin fl = new frmLogin();
fl.Show();