Check if form already Open

[KelsMckin]

Hello, I was wondering if there was a way to check there was already a
form open before opening a new one, sorry that doesnt seem clear, here
is an example:

The following button opens a new form

private void btnAbout_Click(object sender, EventArgs e)
{
avernusAbout About = new avernusAbout();
About.StartPosition = FormStartPosition.Manual;
About.Location = new Point(this.Location.X,
this.Location.Y);
About.Show();
this.Hide();
}

is there a way to check if the form is already open before It opens the
new form?

Any help would be greatly appreciated

 

[Siva M]

If you are using .NET 2.0, use Application.OpenForms as in:

foreach (Form a in Application.OpenForms)
{
if (a is avernusAbout)
{
// About form is open
break;
}
// About form is not open...
}

Hello, I was wondering if there was a way to check there was already a
form open before opening a new one, sorry that doesnt seem clear, here
is an example:

The following button opens a new form

private void btnAbout_Click(object sender, EventArgs e)
{
avernusAbout About = new avernusAbout();
About.StartPosition = FormStartPosition.Manual;
About.Location = new Point(this.Location.X,
this.Location.Y);
About.Show();
this.Hide();
}

is there a way to check if the form is already open before It opens the
new form?

Any help would be greatly appreciated

 

[KelsMckin]

Maybe I should have provided you with a tad bit more information, what
I needed to do if the form was currently open is show it. How could I
go about doing that?

 

[Bruce Wood]

Maybe I should have provided you with a tad bit more information, what
I needed to do if the form was currently open is show it. How could I
go about doing that?

Why not make the Form a singleton? Something like this:

public class MyForm : System.Windows.Forms.Form
{
private static MyForm _instance = null;

private void MyForm()
{
... usual constructor stuff ...
}

public MyForm Instance
{
get
{
if (MyForm._instance == null)
{
MyForm._instance = new MyForm();
}
return MyForm._instance;
}
}
}

Now, whenever you want to show the form, just say:

MyForm.Instance.Show();

No need to search, and it works in .NET 1.1 and 2.0. Will that work for
you?

 

[KelsMckin]

Bruce, I am not sure how to implement that singleton, however I will do
some research on the subject, thankyou all for your help

 

[Matt]

Maybe I should have provided you with a tad bit more information, what
I needed to do if the form was currently open is show it. How could I
go about doing that?

To use the previous poster's example (which is a good one):

foreach (Form a in Application.OpenForms)
{
if (a is avernusAbout)
{
a.TopMost = true; // Moves it to the top of the window stack
// or (if it is simply not visible)
a.Visible = true;
}
// About form is not open...

}

Matt

 

[Guest]

KelsMckin,
Bruce just provided you with a complete working code example of how to do it
as a singleton. All you have to do it try it. There are certainly other ways,
but I'd vote for Bruce's example as being both elegant and simple.
Peter

--
Co-founder, Eggheadcafe.com developer portal:
http://www.eggheadcafe.com
UnBlog:
http://petesbloggerama.blogspot.com

 

[Siva M]

Matt's code should do the trick.

Maybe I should have provided you with a tad bit more information, what
I needed to do if the form was currently open is show it. How could I
go about doing that?

 

[Marc Gravell]

a.TopMost = true; // Moves it to the top of the window stack

IIRC, this toggles the "always on top" behaviour; a combination of
Activate(), Focus() and BringToFront() would probably be more in order,
otherwise the user could find it hard to get rid of the form (to the
background) afterwards.

Marc

 

[Michael Voss]

Bruce Wood wrote:

[...]

Why not make the Form a singleton? Something like this:

[...]

This will work if there'll only ever be one instance of that form. But
sometimes, you'll have to make sure there's only one instnce of a certain
form per business object, e. g. to open a customer form once per customer
and bring it to top otherwise.

We're keeping a Dictionary of our opened forms with a combination of form
class name and business object id as a key and look it up whenever we want
to open a new view, then proceed pretty much as you did...