Click here to Skip to main content
Click here to Skip to main content

MDI child as dialog form (MDI modal workaround)

, 21 Dec 2009 CPOL
Rate this:
Please Sign up or sign in to vote.
Ever had the need to block all other forms and controls when a specific form is shown as a dialog? This is a very simple workaround, for an MDI modal form.


Ever had the need to block all other forms and controls when a specific form is shown as a dialog? This is a very simple workaround, for an MDI modal form.


I was designing an MDI rich application, where I needed a dialog form showing only in the parent form, and blocking the rest of the application, until the user selected something on the dialog form.

Using the code

The code is very, very simple; just inherit the MDIParent form on your MDI parent form instead of the normal form inheritance.

public partial class Your_MDI_Parent_Form : MdiParent

To show a form as a dialog and block other controls, call the ShowChildDialog method on the parent form, like this:

ChildForm frm = new ChildForm();
ShowChildDialog(frm, ChildForm_DialogReturned);

And, to receive the DialogResult from the child form, use the following event receiver:

private void ChildForm_DialogReturned(object sender, DialogResultArgs e)
    MessageBox.Show("ChildForm returned: " + e.Result.ToString());

Explanation of the code

The ShowChildDialog method

public void ShowChildDialog(Form frm, 
       EventHandler<DialogResultArgs> DialogReturnedValue)
    frm.MdiParent = this;
    frm.MaximizeBox = false;
    frm.FormClosed += new FormClosedEventHandler(frm_FormClosed);
    callingsender = frm;
    DialogReturning += DialogReturnedValue;
  1. Set the MDI parent so the form is shown within the parent.
  2. Remove the Maximize button on the child form.
  3. Add an event receiver for the Closed event on the child form; this will be used to return the dialog result from the child dialog form.
  4. callingsender is for internal use, so the code knows which form it is dealing with.
  5. Add an event receiver for the returned dialog result.
  6. Calling the DisableControls method will disable all other controls and forms in the MdiParent.
  7. Last, show the form. This will be the only one enabled.

The DisableControls method

private void DisableControls()
    for (int i = 0; i < this.Controls.Count; i++)
        if (this.Controls[i].GetType() != typeof(MdiClient))
            this.Controls[i].Enabled = false;
    foreach (Form frm in MdiChildren)
        frm.Enabled = false;
    if(callingsender != null)
        callingsender.Enabled = true;
  1. Loop through all the controls of the MDI parent and disable them if it not an MDI child control.
  2. Loop through all the child forms and disable them.
  3. If callingsender is not null, then enable it again.

The ForceReleaseOfControls method

public void ForceReleaseOfControls()
    for (int i = 0; i < this.Controls.Count; i++)
        this.Controls[i].Enabled = true;
    foreach (Form frm in MdiChildren)
        frm.Enabled = true;
  1. Loop through all the controls and enable them again.
  2. Loop through all the child forms and enable them again.

What the code does not do...

This code does not check for the pre-enabled-state of controls and forms. Therefore, it will not remember what enable state the control/form was before, and set it back to that. This can be achieved pretty simply by having a collection of keys and values. But for now, this is the code. Hope it helps those who have the same issues as I did.

Point of interest

I learnt something new about MDI applications.


  • 21. Dec. 2009: First post.
  • 21. Dec. 2009 (later): Updated the article with some explanation of the code.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Comments and Discussions

QuestionExcelent usefull code!!! Pinmembermarianomdq28-Jun-12 22:40 
Your code is great, i'm recently starting with c#. It took me a while to understand it but i think i got the idea.
I'm having some problem now. Sorry if the question is kind of stupid, but i try to figure it out by my self and didn't success.
I get to the point of receive the messagebox with the DialogResult, but what i'm trying to do is something like this:
if (ChildDemoForm_DialogReturned == DialogResult.OK)
(sorry, i know my code seams like it was wrote by a caveman, but i hope you understand what i'm looking for)
I can't find the way to extract the DialogResult for compare it with my desired result.
GeneralRe: Excelent usefull code!!! PinmemberPaw Jershauge28-Jun-12 23:23 
GeneralRe: Excelent usefull code!!! Pinmembermarianomdq29-Jun-12 17:08 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Terms of Use | Mobile
Web02 | 2.8.141223.1 | Last Updated 21 Dec 2009
Article Copyright 2009 by Paw Jershauge
Everything else Copyright © CodeProject, 1999-2014
Layout: fixed | fluid