Recently, I came across a situation where I need to pass value from one Child Form to another Child Form inside an MDI Parent. The scenario was like this. I have an MDI, whose MenuStrip pops out 2 Child Forms together. One child-form lists the Id and Name of all the Employees coming under certain criteria. On double clicking that particular employee, I need to display the value on the second child-form. In short, I need to pass the Id of the employee to the second child-form so that relevant details can be loaded. I’ll simulate the same scenario using a simple example.

Imagine I want to send a value from one of my Child form to display that in my second Child Form. The sample UI looks like this:

[Send Value] –> ChildForm1.cs

   1: /// <summary>

   2: /// Send Value

   3: /// </summary>

   4: /// <param name="sender"></param>

   5: /// <param name="e"></param>

   6: private void button1_Click(object sender, EventArgs e)

   7: {

   8:     ChildForm2 formChild2 = (ChildForm2)this.MdiParent.MdiChildren[1];

   9:     formChild2.ReceiveValue(textBox1.Text);

  10: }

[Receive Value] –> ChildForm2.cs

   1: // Receive Value

   2: public void ReceiveValue(string value)

   3:         {

   4:             textBox1.Text = value;

   5:             this.Activate();

   6:             this.Refresh();

   7:         }

VB.NET

[Send Value] –> ChildForm1.vb

   1: Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

   2:  

   3:         Dim formChild2 As ChildForm2 = DirectCast(Me.MdiParent.MdiChildren(1), ChildForm2)

   4:         formChild2.ReceiveValue(TextBox1.Text)

   5:  

   6:     End Sub

[Receive Value] –> ChildForm2.vb

   1: Public Sub ReceiveValue(ByVal value As String)

   2:        TextBox1.Text = value

   3:        Me.Activate()

   4:        Me.Refresh()

   5:    End Sub

Hope this helps.

Thanks