C# mdi between three forms

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i have 3 forms i.e form1,form2 & form3.
and set ismdicontainer is true in form1.

form1 button click for form2 open

// // Form1.IsMdiContainer should be true
            //Form1 form1 = new Form1();
            // This automatically adds form2 into form1's MdiChildren collection
            Form2 form2 = new Form2();
            form2.MdiParent = this;
            form2.Show();

now when i want to open form3 child in form1 mdiparent.below i tried code but not solved.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Mdi_3Forms
{
    public partial class Form2 : Form
    {
        // Include as data member so we only instantiate one Form3
        Form3 _form3;
        Form1 form1;
        public Form2()
        {
            InitializeComponent();
            button1.Click += new EventHandler(button1_Click);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (_form3 == null)
            {
                this.Close();
                _form3 = new Form3();
                // Set Form3's parent to be Form1
                _form3.MdiParent = this.form1;
                _form3.Show();
            }

        }
    }
}

form2 closed but form3 is not set mdi child in form1.
pls help with solution.

sorry for my bad english.
many thanks.

What I have tried:

Form1.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Mdi_3Forms
{
    public partial class Form1 : Form
    {
        
        public Form1()
        {
            
            InitializeComponent();
           
        }
         

        private void button1_Click(object sender, EventArgs e)
        {
           // // Form1.IsMdiContainer should be true
            //Form1 form1 = new Form1();
            // This automatically adds form2 into form1's MdiChildren collection
            Form2 form2 = new Form2();
            form2.MdiParent = this;
            form2.Show();
           
        }
    }

Form2

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Mdi_3Forms
{
    public partial class Form2 : Form
    {
        // Include as data member so we only instantiate one Form3
        Form3 _form3;
        Form1 form1;
        public Form2()
        {
            InitializeComponent();
            button1.Click += new EventHandler(button1_Click);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (_form3 == null)
            {
                this.Close();
                _form3 = new Form3();
                // Set Form3's parent to be Form1
                _form3.MdiParent = this.form1;
                _form3.Show();
            }

        }
    }
}

Posted 3-Apr-20 20:17pm

Member 10570811

Updated 4-Apr-20 5:36am

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Maciej Los 4-Apr-20 11:17am

Please, do NOT repost!
C# mdi between three forms[^]

2 solutions

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OriginalGriff · Answer 1 · 2020-04-03T21:28:00

The whole idea is that you don't do it that way: Form2 shouldn't know Form1 exists, much less Form3, let alone be responsible for displaying it!
Instead, Form2 should talk to Form1, tell it it has a user request and let Form1 handle what it does with it: that could be a MessageBox, or it could open a new Form2, or a Form3; or it could activate an existing Form3 that Form2 knows nothing about - that's up to the parent form, not the child.

That sounds complicated, but it isn't, not really. Have a look at this: Transferring information between two forms, Part 2: Child to Parent[^] and it will show you how, and even give you sample code you can adapt to your specific needs.

Maciej Los · Answer 2 · 2020-04-04T05:38:00

Seems, you just want to open child form in this schema:
Form1 has to be a main form. Form2, Form3, etc.has to be a child form.
The order of opening forms is:
Form1 -> Form2 -> Form3

Every child form constructor has to be changed to:

C#

public Form2(Form ParentForm)
{
    InitializeComponent();
    this.MdiParent = ParentForm;
}


public Form3(Form ParentForm)
{
    InitializeComponent();
    this.MdiParent = ParentForm;
}

Usage:

C#

//in Form1
private void button1_Click(object sender, EventArgs e)
{
    Form2 form2 = new Form2(this);    //refers to Form1
    form2.Show();
}

//in Form2
private void button1_Click(object sender, EventArgs e)
{
    Form3 form3 = new Form3(this.MdiParent); //refers to Form2.MdiParent, which is Form1
    form3.Show();
}

C# mdi between three forms

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Solution 1

Solution 2

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