How to stop multiple instances of mdi form from opening

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I have an MDI parent form that holds my mdi child forms and what I am trying to achieve is to stop multiple instances of the children form from opening. So far I have been able to achieve this i.e when a child form instance is open, another instance of the child form cannot be open. The problem I have now is, when i close the child form, it does not open again until i restart the application. Below is a snippet from my code so far.

C#

public partial class DataMigrationMDI : Form
   {

       ConnectToSource src_mdi_child = null;

       public DataMigrationMDI()
       {
           InitializeComponent();

       }

        private void connectToSourceDatabaseToolStripMenuItem_Click(object sender, EventArgs e)
       {
           if (src_mdi_child == null)
           {
               src_mdi_child = new ConnectToSource();
               src_mdi_child.MdiParent = this;
               src_mdi_child.Show();
           }

       }

   }

So,basically I initially set the child form instance to null and then at the onclick event of the toolstrip i check if the child form is null and then opens it. But with this code it doesn't check when the child form is closed to re-assign it back to null so that in this way the child form can be re-opened. So the help I need is to be shown how to check when a child form has been closed and then assign it back to null. Thanks in advance

Posted 11-Oct-13 1:24am

Uzoma Umekwe

Updated 11-Oct-13 1:27am

v4

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Ehsan Skardu · Answer 1 · 2013-10-11T02:24:00

Solution 2

Hello Uzoma

Call this function before the code opening the any child,

private void CloseMdichilds()
        {
            this.MdiParent.MdiChildren.OfType<Form>().ToList().ForEach(x => x.Close());
        }

Posted 11-Oct-13 2:24am

Ehsan Skardu

Comments

Uzoma Umekwe 11-Oct-13 8:59am

Hi ehsan..thanks for your answer.but I really dont understand what the code does...where exactly I am to call this function and how does the code actually check that a child form is closed and then assign it a null value?

[no name] 11-Oct-13 11:24am

I am sorry i could not explain. ok I will try again,
As this function will close all the open mdichild forms so when ever you are going to open a new child form you will call this function and then open the new one.

Maciej Los · Answer 2 · 2013-10-11T03:02:00

Solution 3

I would recommend to read Sergey's answers about using MDI[^].

Sergey Alexandrovich Kryukov wrote:
Here is the best way of using MDI child: never using MDI.

Here is the idea: who needs MDI, ever? Why torturing yourself and scaring off your users?

Posted 11-Oct-13 3:02am

Maciej Los

Vishnu Prajapati · Answer 3 · 2013-10-11T03:23:00

Solution 4

C#

class ParentForm : Form {
    frmWebLeads formWeblead = null;

    //...

    private void leadsToolStripMenuItem_Click(object sender, EventArgs e)
    {
        if(formWeblead != null) return;
        formWeblead = new frmWebLeads();
        formWeblead.MdiParent = this;
        formWeblead.WindowState = System.Windows.Forms.FormWindowState.Maximized;
        formWeblead.Show();

    }

}

Posted 11-Oct-13 3:23am

Vishnu Prajapati

Comments

Uzoma Umekwe 11-Oct-13 9:49am

Hi Vishnu..your code is no much different from what I already have.what i want to achieve is to assign the child form to null after it closes...

Uzoma Umekwe · Answer 4 · 2013-10-11T05:38:00

Alright guys..Thanks to all of you for your help and ideas..Well I was able to sort this after several hours of head-banging :)

C#

private void connectToSourceDatabaseToolStripMenuItem_Click(object sender, EventArgs e)
      {
          if (src_mdi_child == null || src_mdi_child.IsDisposed)
          {
              src_mdi_child = new ConnectToSource();
              src_mdi_child.MdiParent = this;
              src_mdi_child.Show();
          }
      }

So I added the IsDisposed property. The condition checks if the childform is null and if it has been previously disposed before opening the form. Tada! it works!