C# 限制窗体弹窗显示必须关闭后才能重新实例化窗体

主窗体Form1

弹窗窗体Form2

在主窗体Form1的Button点击事件中加入：

private void btnXXX_Click(object sender, EventArgs e)
{
    if (Form2.Instance == null || Form2.Instance.IsDisposed)
    {
        Form2 frm = new Form2();
        Form2.Instance.Show();
    }
    else
    {
        Form2.Instance.Activate();
    }
}

在弹窗窗体Form2中加入：

private static Form2 _instance = null;
public static Form2 Instance { get { return _instance; } }
        
public Form2()
{
    InitializeComponent();
    _instance = this;
}

private void Form2_FormClosed(object sender, FormClosedEventArgs e)
{
    _instance = null;
    this.Dispose();
}