Simple C# Question

[Venkrishna]

Hi Guys,

I am calling only one instance of Form2 when I click on the datagrid on the Form1. The Form2 appears but when the focus is lost for the Form2 I cannot see Form2 anymore. No idea where it has gone!!

As I am calling only one instance of the Form2 clicking any number of times on the datagrid never brings up the Form2.

Any ideas?

[DeadEyes]

Can't say anything other than, Form2 is hiding behind Form1, without seeing some code.

[Venkrishna]

Hi DeadEyes,

Thanks for an early reply.

Sorry, I am unable to provide the code at the moment as I am not at that Site but Form1 Calls Form2 as only 1 instance. This is an MDI application and Form2 is not called from MDI menus but called only from Form1 which has MDI form as the MDIParent.

Any sample code please help.

[Andy]

is form2 designed to be shown in the taskbar? how are you instantiating and showing form2?

[Venkrishna]

HI Andy,

Form2 is not designed to be shown in Taskbar.

I have taken an example from C# forums in other site to create a bool variable
as

public static bool IsOpen = false;

and

when the Form2 is being opened from Form1
the code is as below. When the user clicks on the product id on the datagrid it would bring up the Form2

private void dgProducts_MouseUp(object sender, MouseEventArgs e)
		{
			System.Drawing.Point pt = new Point(e.X, e.Y); 
			DataGrid.HitTestInfo hti = dgProducts.HitTest(pt); 
			if(hti.Type == DataGrid.HitTestType.Cell) 
			{ 
				dgProducts.CurrentCell = new DataGridCell(hti.Row, hti.Column); 
				dgProducts.Select(hti.Row); 
			 
			sProductId = dgProducts[hti.Row,0].ToString();

			if (sProdId != "")
			{
				if (!Form2.IsOpen)
				{
					Form2 frm2= new Form2();
					frm2.sProdId = this.sProductId;
					frm2.Show();
				}
			}
			}

		}

The instance of Form2 shows up but when the focus is lost I cannot find the Form2 anywhere!

[Andy]

Could you also post the code for form2? Specifically the section InitializeComponents, and Form2_Load.

that's where I'd start looking. It seems to be a problem with form2.

[jmcilhinney]

How about

if (Form2.IsOpen)
{
    myForm2Instance.Activate();
}
else
{
    // Create a new instance and display.
}

[Venkrishna]

jmcilhinney,

In your code

if (Form2.IsOpen)
{
    myForm2Instance.Activate();
}
else
{
    // Create a new instance and display.
}

Where will the object myForm2Instance first be created / declared?


Edit: Added [code][/code] tags for clairty. - Hack

[jmcilhinney]

Form2 doesn't need any code. This should work "as is" as long as the instance of Form2 has not had Hide called on it, its Visible property set to False or had Close called on it. In the previous code I posted, I'd suggest putting a breakpoint on the line that activates the existing instance of Form2 and use the Locals or Watch window to examine all the properties of that object. I'd be looking specifically at Visible, Location, WindowState, IsDisposed and anything else that might cause it to not be seen.

[Venkrishna]

jmcilhinney,

I dont know where I have lost the code i have used before.

Can you please send me sample code both activating and opening only one instance of the Form2 from Form1 if you dont mind.

In your code

if (Form2.IsOpen)
{
myForm2Instance.Activate();
}
else
{
// Create a new instance and display.
}

Where will the object myForm2Instance first be created / declared?

[jmcilhinney]

Here's what I would do. I'd forget that IsOpen variable altogether. Declare a variable of type Form2 as a member of Form1 and use it like this:

private Form2 myForm2;

private void ShowForm2()
{
    if (this.myForm2 == null || this.myForm2.IsDisposed)
    {
        // Create a new instance of Form2.
        this.myForm2 = new Form2();
        this.myForm2.Show();
    }
    else
    {
        // If myForm2.Visible has been set to False then change that here.
        // Activate the existing instance.
        this.myForm2.Activate();
    } 
}

I hope my syntax is all correct. I do most of my work in VB and sometimes some VB syntax can sneek in when I don't copy and paste. Note that this code is all in Form1.

[Venkrishna]

Hello people,

Atlast I have found some info from

http://msdn.microsoft.com/smartclien...q/default.aspx

In this page there is a topic called
Creating Forms and Controls

and there is a topic

How do I ensure that no more than one instance of modeless dialog is created or open at a time?

This solved my problem and I am quite happy with it.

[jmcilhinney]

This solution will certainly work but using owned forms does have other implications. I'd suggest reading the help topic for the "Form.OwnedForms Property" just to check whether you find these implications good, bad or indifferent.

Edit:
Note that the article you cite talks about modeless dialogues rather than just windows in general. The VS.NET Find and Replace dialogue is an example of a modeless dialogue. It displays the behaviour of an owned form.