Unable to Open ChildForm inside MdiParent

Question

I am trying to open ChildForms on MdiParent Form using a Form Manager Class. I've tried several alternatives in order to tell "FormManager" Class which Form is the MdiParent; however it would always throw errors (1 different error for each different occasion). Most of the times it would say that MainForm was not a MdiContainer; and this is not true as I had set MainForm previously as such.

Note:1 Main Form is set as a MdiContainer.

Note:2 If I attempt to open only 1 Form it will open perfectly inside MdiParent Form. However if I attempt to Load 2 or more Forms it will throw error.

Note:3 If I create the Child Forms Instances on Main Form; Everything works just fine. No issues at all. But this is not how I want to do it.

  // [Class] : Main Form
  // Member Variables
  private FormManager FrmMgr;

  // Load Forms using FormManager Class
  private void Load_Forms()
  {
  // Create a new Instance of FormManager.
      if (FrmMgr == null) { FrmMgr = new FormManager(); }
  // Set MainForm as MdiParent in FormManager Class
      FrmMgr.MdiParent = this;
  // Alternatively Manually Set the MdiParent in MainForm (Uncomment Line Bellow)
  // this.IsMdiContainer = true;
  }


  // [Class] : Form Manager
  // <Member Variables>
  private Form1 frm1;
  private Form2 frm2;

  // FormManager <Constructor>.
  // Constructor Receives MdiParent Information from MainForm
  // and Sets the MdiParent.ActiveControl Information to Every Form
  // when calling each (Form initiation) Method.
   public FormManager(Form _MainParent)
   {
       // Create new Instance of Form1
       Init_Frm1(_MainParent);

       // Create new Instance of Form2
       Init_Frm2(_MainParent);
   }

    private void Init_frm1(_MainParent)
    {
        if (frm1 == null) { frm1 = new Form1(); }
        frm1.MdiParent = _MainParent;

        frm1.Show();
    }

    private void Init_frm2(_MainParent)
    {
        if (frm2 == null) { frm2 = new Form2(); }
        frm2.MdiParent = _MainParent;

        frm2.Show();
    }
}

Can anyone point me in the right direction and help me understand why this happens? Thanks in advance.

Answer 1

I was finally able to sort it out.

The issue seemed to be consisted in the way I've used to pass "MainForm" as the "MdiParent" to "FormManager" class.

// [Class] MainForm
// Create new Instance (Always Active); of FormManager Class
// Note: When FormManager Class is Loaded; it's Constructor will
// run the Methods that will open all the initial Forms.

private void Load_Modules()
{
    // "this" refers to "MainForm"
    if (FrmMgr == null) { FrmMgr = new FormManager(this); }
}


// [Class] FormManager
// Member Variables
private Form1 frm1;
private Form2 frm2;

// <Constructor>
public FormManager(Form _MainParent)
{
    // Create new Instance of Form1 under "Init_Frm1" Method
    Init_Frm1(_MainParent);

    // Create new Instance of Form2 under "Init_Frm2" Method
    Init_Frm2(_MainParent);
}

// Method that Will Create new Instance of Form1
private void Init_Frm1(Form _MainParent)
{
    if (frm1 == null) { frm1 = new Form1(); }
    frm1.MdiParent = _MainParent;

    frm1.Show();
}

// Method that Will Create new Instance of Form2
private void Init_Frm2(Form _MainParent)
{
    if (frm2 == null) { frm2 = new Form2(); }
    frm2.MdiParent = _MainParent;

    frm2.Show();
}