C#中避免相同MDI子窗口重复打开的方法

方法一：

直接检测是否已经打开此MDI窗体

// 是否已经打开了？（用循环来判断）
foreach (Form childrenForm in this.MdiChildren)
{
//检测是不是当前子窗体名称
if (childrenForm.Name == "子窗体名称")
{
//是的话就是把他显示
childrenForm.Visible = true;
//并激活该窗体
childrenForm.Activate();
return;
}
}
//下面是打开子窗体
Form1 childrenForm = new Form1();
childrenForm.MdiParent = this;
childrenForm.Show();
childrenForm.WindowState = FormWindowState.Maximized;
方法二：

将子窗体设成单件：

namespace WindowsFile
{
public partial class Form3 : Form
{
public Form3()
{
InitializeComponent();
}

private void Form3_Load(object sender, EventArgs e)
{
richTextBox1.LoadFile(".//test.txt", RichTextBoxStreamType.PlainText);
}
private static Form3 childform=null;
public static Form3 Form3Signleton()
{
if (childform == null)
{
childform = new Form3();
}
return childform;
}
private void Form3_FormClosing(object sender, FormClosingEventArgs e)
{
try
{

this.Dispose(true);
childform = null;
}
catch(Exception e)
{ MessageBox(e.ToString()); }
}
方法三：

这个没用过，也是直接判断

private static frm_rk frmchild;//定义子窗体

private void 商品入库ToolStripMenuItem_Click(object sender, EventArgs e)//按钮事件
{
frm_rk frmchild = GetForm();
frmchild.Show();
}
private frm_rk GetForm()//判断子窗体状态，防止重复显示
{

if (frmchild == null || frmchild.IsDisposed)
{
frmchild = new frm_rk();
frmchild.MdiParent = this;
}
return frmchild;
}