How to show(Bringtofront) an already opened Mdi child form from another Mdi child form?

Question

In my applcation i have 4 forms ,form1 is a mdi container and remaining forms are it childs, in form1 i am opening all child form in its load event. in child form2 i have a button which will switch to childform3.my problem is how to show childform3(which is already opened) from button in childform2

               form1:

               Form2 formchild1;
               Form3 formchild2;
               Form4 formchild3;

        private void Form1_Load(object sender, EventArgs e)
        {


        if (formchild2 == null)
        {
            formchild2 = new Form3();
        }
        formchild2.MdiParent = this;
        formchild2.Dock = DockStyle.Fill;
        formchild2.Show();
        //formchild2.BringToFront();


        if (formchild3 == null)
        {
            formchild3 = new Form4();
        }
        formchild3.MdiParent = this;
        formchild3.Dock = DockStyle.Fill;
        formchild3.Show();


        if (formchild1 == null)
        {
            formchild1 = new Form2();
        }
        formchild1.MdiParent = this;
        formchild1.Show();
        formchild1.Dock = DockStyle.Fill;
        formchild1.BringToFront();


        }


        form2:

        Form3 formchild2;
   private void button1_Click(object sender, EventArgs e)
    {
        //what i have to write hare..
            //formchild2 = new Form3();
            //formchild2.MdiParent = this.ParentForm;

            //formchild2.Dock = DockStyle.Fill;
            //formchild2.Show();
            //formchild2.BringToFront();

    }

Answer 1

When you create your form2 (Please change your variable names, it took a while to figure out that formchild1 was actually form2), you need to instantiate the form2 instance

if (formchild1 == null)
{
    formchild1 = new Form2(/*Either pass in a Form3 here*/);
}
formchild1.formChild2 = formchild2; //Or make formChild2 public member
formchlid1.SetForm(formChild2); //Or make a method that sets it
formchild1.MdiParent = this;
formchild1.Show();
formchild1.Dock = DockStyle.Fill;
formchild1.BringToFront();

Then to show it again you can just do

formchild2.BringToFront();

Answer 2

childform3 childform3=new childform3;

private void button1_Click(object sender, EventArgs e)
    {
        if (!childform3.IsDisposed)
            childform3.Select();
        else
            childform3= new frmSearch();
        childform3.MdiParent = ParentForm;
        childform3.Show();
    }