如何避免在 .NET Windows Forms 中创建重复的表单?

问题描述

我正在使用 .NET Windows 窗体.我的 MDI 父窗体包含菜单.如果单击菜单，将显示表单.到目前为止没有问题.

I am using .NET Windows Forms. My MDI parent form contains the menu. If click the menu the form will be displayed. Up to now no problem.

UserForm uf = new UserForm();
uf.Show();
uf.MdiParent = this;

如果我再次单击菜单，则会创建表单的另一个副本.如何解决这个问题?

If I click the menu again another duplicate of the form is created. How to solve this issue?

推荐答案

最简洁的方法是简单地跟踪表单实例的生命周期.通过订阅 FormClosed 事件来实现.例如:

The cleanest way is to simply track the lifetime of the form instance. Do so by subscribing the FormClosed event. For example:

    private UserForm userFormInstance;

    private void showUserForm_Click(object sender, EventArgs e) {
        if (userFormInstance != null) {
            userFormInstance.WindowState = FormWindowState.Normal;
            userFormInstance.Focus();
        }
        else {
            userFormInstance = new UserForm();
            userFormInstance.MdiParent = this;
            userFormInstance.FormClosed += (o, ea) => userFormInstance = null;
            userFormInstance.Show();
        }
    }