Application.Run(new FormMain());//設置應用程序運行時加載的窗口

private void button1_Click(object sender, EventArgs e)//登錄
{
if (this.textBoxPassword.Text == "")
{
MessageBox.Show("請輸入密碼！");
}
else if (this.textBoxUsername.Text=="123" && this.textBoxPassword.Text == "123")
{
this.DialogResult = DialogResult.OK;
this.Close();
}
else
{
MessageBox.Show("Username or Password Error");
}
}

private void main_Load(object sender, EventArgs e)
{
Form formLogin = new login();
formLogin.ShowDialog();
if (formLogin.DialogResult == DialogResult.OK)//如果登錄框返回DialogResult.OK
{
MessageBox.Show("正常登錄");
}
else
{
this.Close();
}
}

Form formLogin = new login();
formLogin.ShowDialog();
if (formLogin.DialogResult == DialogResult.OK)
{
Application.Run(new formMain());
}
else
{
return;
}