我无法再次打开 MDI Parent 中的 2 个 Window Childs

Question

I created a MDI Parent Form (Form1), that has 1 Menu with 2 Items. Each Item opens a Window Child (Form2 and Form3). I can open Form2 and Form3, if they are already open they just got the focus. So far, everything's Ok. The problem is when i close Form2 and Form3, i can't open them again? Can anyone help me with this. Many thanks.

using System;
using System.Drawing;
using System.Windows.Forms;

namespace App51
{
  public partial class Form1 : Form
  {
    Form2 frm2 = Application.OpenForms["Form2"] as Form2;
    Form3 frm3 = Application.OpenForms["Form3"] as Form3;


public Form1()
{
  InitializeComponent();
}


private void Form1_Load(object sender, EventArgs e)
{
  this.WindowState = FormWindowState.Maximized;
  IsMdiContainer = true;
  foreach (Control control in this.Controls)
    if (control is MdiClient)
    {
      control.BackColor = Color.DeepSkyBlue;
      break;
    }
}
  

private void abrirForm2ToolStripMenuItem_Click(object sender, EventArgs e)
{
  if (frm2 != null)
  {
    frm2.WindowState = FormWindowState.Normal;
    frm2.BringToFront();
    frm2.Activate();
  }
  else
  {
    frm2 = new Form2();
    frm2.MdiParent = this;
    frm2.Show();
  }
}


private void abrirForm3ToolStripMenuItem_Click(object sender, EventArgs e)
{
  if (frm3 != null)
  {
    frm3.WindowState = FormWindowState.Normal;
    frm3.BringToFront();
    frm3.Activate();
  }
  else
  {
    frm3 = new Form3();
    frm3.MdiParent = this;
    frm3.Show();
  }
}

} }

Answer 1

I changed the code a bit. Now it works:) What do you think of it?

using System;
using System.Drawing;
using System.Windows.Forms;

namespace App51
{
  public partial class Form1 : Form
  {
    Form2 frm2 = new Form2();
    Form3 frm3 = new Form3();


public Form1()
{
  InitializeComponent();
}


private void Form1_Load(object sender, EventArgs e)
{
  this.WindowState = FormWindowState.Maximized;
  IsMdiContainer = true;
  foreach (Control control in this.Controls)
    if (control is MdiClient)
    {
      control.BackColor = Color.DeepSkyBlue;
      break;
    }
}
  

private void abrirForm2ToolStripMenuItem_Click(object sender, EventArgs e)
{
  if (frm2 != null)
  {
    if (frm2.Visible == true)
    {
      frm2.WindowState = FormWindowState.Normal;
      frm2.BringToFront();
      frm2.Activate();
    }
    else
    {
      frm2 = new Form2();
      frm2.MdiParent = this;
      frm2.Show();
    }
  }
}
  

private void abrirForm3ToolStripMenuItem_Click(object sender, EventArgs e)
{
  if (frm3 != null)
  {
    if (frm3.Visible == true)
    {
      frm3.WindowState = FormWindowState.Normal;
      frm3.BringToFront();
      frm3.Activate();
    }
    else
    {
      frm3 = new Form3();
      frm3.MdiParent = this;
      frm3.Show();
    }
  }
}

} }