Mdi Child forms single instance

Question

Im making an MDI Windows forms app in c#, I am tryig to make the mdi child forms to open in a single instance. I am using this sample code in my button_click event in a new project just for testing purposes and it works fine there, but when I implement this code in my main project it just does nothing. I am providing the exact same conditions as in the test project but it won't work. I just cannot understand why.

Both forms have the same MDI parent. Form1 loads with the MDI parent.

Button click event in Form1 for openning Form2:

    private void button1_Click(object sender, EventArgs e)
    {
        if (System.Windows.Forms.Application.OpenForms["Form2"] as Form2 == null)
        {
            Form2 F2 = new Form2();
            F2.MdiParent = this.MdiParent;
            F2.Show();
        }
        else 
        {
            Form2 F2 = (Form2)Application.OpenForms["Form2"];
            F2.Focus();
        }
    }

Here is some more info:

The MDI parent is the starting Form for the project.

The Form Load of the MDI parent is as follows:

    private void MDI_Load(object sender, EventArgs e)
    {
        Form1 F1 = new Form1();
        F1.MdiParent = this;
        F1.Show();
    }

Answer 1

Try specifically setting the name "Form2" to F2 when you create it, f2.name = "Form2". That is how the OpenForms collection addresses it.

Answer 2

I agree that the scope of the Form is an issue here. This is how I open a Form inside my main mdi form:

public partial class FormMain : Form
{
    FormTest ftmTest;

    ...

    void testToolStripMenuItem_Click(object sender, EventArgs e)
    {

        if(frmTest == null)
        {
            frmTest = new FormTest();
            frmTest.MdiParent = this;
        }
        frmTest.Show();
        frmTest.BringToFront();
    }

Answer 3

MdiChildren aren't added to Application.OpenForms collection.

You need to check the MdiChildren() collection of the MdiParent:

    private void button1_Click(object sender, EventArgs e)
    {
        foreach (Form frm in this.MdiParent.MdiChildren)
        {
            if (frm is Form2)
            {
                if (frm.WindowState == FormWindowState.Minimized)
                    frm.WindowState = FormWindowState.Normal;
                frm.Focus();
                return;
            }
        }
        Form2 F2 = new Form2();
        F2.MdiParent = this.MdiParent;
        F2.Show();
    }

Answer 4

my solution

code:

View.FormV view = Application.OpenForms["FormV"] as View.FormV ;
        if(view == null)
        {
            View.FormV View = new FormV();
            View.MdiParent = this;
            View.Show();
        }
        else
        {
            view.Focus();
        }

Answer 5

private void button1_Click(object sender, EventArgs e)
{
    foreach (Form frm in this.MdiChildren)
    {
        if (frm is Form2)
        {
            if (frm.WindowState == FormWindowState.Minimized)
                frm.WindowState = FormWindowState.Normal;
            frm.Focus();
            return;
        }
    }
    Form2 F2 = new Form2();
    F2.MdiParent = this;
    F2.Show();
}

Answer 6

My sample

public partial class Form1: Form
{
    Form frm= new Form2();
    
    .........

        if (frm.IsDisposed) 
        {
            frm= new Form2(); 
        }
        frm.MdiParent = this;
        frm.WindowState = FormWindowState.Maximized;
        frm.Show();
        frm.BringToFront();
    
}