MDI one Child instance.

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scole954387@gmail.com - 28 Sep 2006 04:13 GMT

Hi,

I'm creating a MDI application and running into the common problem of
more than one instance of the child form. I've read several articles
and postings on the Singleton approach, but I can't get it to work.

What I have:

One form with linklabels and another form with a webbrowser. When the
linklabel is clicked the webbrowser navigates to the url. The problem
is each time a linklabel is clicked a new webbrowser form opens.

I'm trying to have the one webbrowser form update to the new url with
each click of a linklabel rather than having multiple webbrowser forms
opening.

Do anyone have any idea on how to do this. Keep in mind that I am very
new to visual studio and c# programming. Example code is best.

Thanks a bunch,
S. Cole

Reply to this Message

Steven Nagy - 28 Sep 2006 07:32 GMT

Hi

Sure. Singleton is definately the right approach.
Create a form level declaration of your Form in the parent container
form.
When the link label is clicked, have it check first if the form
instance is null. If it is, then initialise it. Then simply call the
usual mdi parent stuff and show the form.

Eg.
private MyForm as SomeForm
void MyLabel_OnClick(blah blah blah) {
if (MyForm == null) {
MyForm = new SomeForm();
// whatever else needs declaring, like setting form parent.
}
MyForm.Show();
}

Reply to this Message

scole954387@gmail.com - 28 Sep 2006 13:43 GMT

Thanks for the information, but I can't get it to work.

main form - parent mdi
form 1 - link labels
form 2 - webbrowser

My code...
private void lnkGoogle_LinkClicked(object sender,
LinkLabelLinkClickedEventArgs e)
{
if (frmContentDisplay == null)
{
frmContentDisplay objChildContentDisplay = new
frmContentDisplay();
objChildContentDisplay.MdiParent = this;
}
objChildContentDisplay.Show();
objChildContentDisplay.LoadURL("http://www.google.com");

}

and I get the following errors...

Error    1 'CDV_My_Agent.frmContentDisplay' is a 'type' but is used like a
'variable'
Error    2    The name 'objChildContentDisplay' does not exist in the current
context
Error    3    The name 'objChildContentDisplay' does not exist in the current
context

The form is initially loaded by the main mdi window with...

// Show ContentDisplay window on Startup
frmContentDisplay objChildContentDisplay = new
frmContentDisplay();
objChildContentDisplay.MdiParent = this;
objChildContentDisplay.Show();

//objChildContentDisplay.LoadURL("http://www.anything.com");

> Hi
>
[quoted text clipped - 14 lines]
> MyForm.Show();
> }

Reply to this Message

Steven Nagy - 28 Sep 2006 21:20 GMT

Try this:

frmContentDisplay objChildContentDisplay;

LinkLabelLinkClickedEventArgs e)
{
if (objChildContentDisplay==null)
{
frmContentDisplay objChildContentDisplay = new
frmContentDisplay();
objChildContentDisplay.MdiParent = this;
}
objChildContentDisplay.Show();
objChildContentDisplay.LoadURL("http://www.google.com");

}

Reply to this Message

S. Cole - 29 Sep 2006 01:55 GMT

Hey,

Thanks for the help. Here's the errors received...

Error    1    The name 'objChildContentDisplay' does not exist in the current
context
Error    2    The name 'objChildContentDisplay' does not exist in the current
context
Error    3    The name 'objChildContentDisplay' does not exist in the current
context

I'm assuming that this is happening because there's no such thing as
objChildContentDisplay until the frmContentDisplay
objChildContentDisplay = new frmContentDisplay(); is parsed. And I'm
assuming that this is not getting parsed because of the
objChildContentDisplay==null statement. Any ideas?

I have the parent form opening the ContentDisplay form (webbrowser
form) under the _Load function. Should I have the linklabel child form
open it instead?

Thanks,
S. Cole

> Try this:
>
[quoted text clipped - 12 lines]
>
> }

Reply to this Message

Steven Nagy - 29 Sep 2006 23:49 GMT

Sorry, I made a mistake in the code I wrote!
I redeclared a variable with the same name when I ment to use the same
form level variable.
Here's the new code (spot the difference!) :

> > frmContentDisplay objChildContentDisplay;
> >
[quoted text clipped - 10 lines]
> >
> > }

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MDI one Child instance.

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