Controlling Multiple Forms in C#

Garth Edmunds

This is my first question so I hope I am doing this right. I am currently using Visual Studio Express 2017 doing a C# Windows Forms App project.

I have searched through Stack Overflow and YouTube for a similar examples but could find none. In the image attached, I have 3 forms in the project. Form1 which is the main controlling form and has 2 buttons on it. Form2button for Form2 and Form3button for Form3. When I click From2button, I can keep clicking and open multiple Form2's as well open multiple Form3's without limitations. I would like to run the program that if I click on Form2button it can only load one instance of Form2 and the same with Form3button.

However if I click Form3button and Form2 is open, I want Form2 to close and only have Form3 open as well as is Form3 is open and I click on Form2button, Form3 will close and Form2 will open. All the time Form1 is active on the screen.

namespace MultiWindows

{ public partial class Form1 : Form { public Form1() { InitializeComponent(); }

private void Form2button_Click(object sender, EventArgs e)

Form2 f2 = new Form2();

f2.Show();

private void Form3Button_Click(object sender, EventArgs e)

Form3 f3 = new Form3();

f3.Show();

}

4 Replies

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Jaish Mathews8y ago
For a way to open the either Forms again without restarting the program, you can make form variable null inside form close event handler.
private void Form2Button_Click(object sender, EventArgs e)
        {
            if (this.f2 == null)
            {
                f2 = new Form2();
                f2.FormClosed += F2_FormClosed;
                f2.Show();
            }
            else
            {
                f2.BringToFront();
            }
        }

        private void F2_FormClosed(object sender, FormClosedEventArgs e)
        {
            f2 = null;
        }

        private void Form3Button_Click(object sender, EventArgs e)
        {
            if (this.f3 == null)
            {
                f3 = new Form3();
                f3.FormClosed += F3_FormClosed;
                f3.Show();
            }
            else
            {
                f3.BringToFront();
            }
        }

        private void F3_FormClosed(object sender, FormClosedEventArgs e)
        {
            f3 = null;
        }
Garth Edmunds8y ago
Jaish,

The code below works great for only opening one instance of Form2 or Form 3 Thanks.
If Form2 is open and I click Form3 button I would like it to close Form2 or vice versa from Form3 to Form2.

Also if I close Form2 by mistake I have to restart the program all over again. Is there a way to open the either Forms again without restarting the program?
Jaish Mathews8y ago
1st of all MDI window to use for controlling multiple Forms. That's the right way on UI perspective. If you question is for learning purpose, then you want to arrange your code like below.
Declare 2 private class variables
Then check these variables before using to show Forms
private Form2 f2 = null;
private Form3 f3 = null;

private void Form2Button_Click(object sender, EventArgs e)
        {
            if (this.f2 == null)
            {
                f2 = new Form2();
                f2.Show();
            }
            else
            {
                f2.BringToFront();
            }
        }

        private void Form3Button_Click(object sender, EventArgs e)
        {
            if (this.f3 == null)
            {
                f3 = new Form3();
                f3.Show();
            }
            else
            {
              f3.BringToFront();
             }

        }
Suraj Kumar8y ago
Hello Garth,
You can create a class which will contain a property of name GetActiveForm to store the active form as below

public static string GetActiveForm
{
get { return activeForm; }
set { activeForm = value; }
}
On clicking another button to open the other form first check the value of GetActiveForm and take the action as below

if (CRMPro.BOObjects.Common.Global.GetActiveForm != "" || CRMPro.BOObjects.Common.Global.GetActiveForm == "frmItemCategoryView" || CRMPro.BOObjects.Common.Global.GetActiveForm == "frmItemCategory")
{
MessageBox.Show("First complete the existing process", this.Text, MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
this.Cursor = Cursors.Default;
return;
}
else
{
frmItemCategoryView objView = new frmItemCategoryView();
CRMPro.BOObjects.Common.Global.GetActiveForm = "frmItemCategoryView";
objView.MdiParent = this;
objView.Show();
objView = null;
}

Based on the value of GetActiveForm you can check whether any form is already open or not and can restrict also to open same form.

Thanks
Suraj