Visual Basic

8-Feb-07 6:35

How to dissallow the user to open an opened form

I mean dont allow to create many instance of the same form
(if form is open dont open it again

Regards
Ramy

MatrixCoder8-Feb-07 6:41

MatrixCoder

8-Feb-07 6:41

Goto the "Project->Project Properties->Application" menu in VS, and then click the "Make single instance application" check box.

Trinity: Neo... nobody has ever done this before.
Neo: That's why it's going to work.

charchabil038-Feb-07 7:11

8-Feb-07 7:11

i checked it
but more then one instance are still running

note i am using the following

dim fr as new form1<br />
fr.show()

do u think is there a problem with the above code?
anything should be added to it

Regards
Ramy

Re: instance of form [modified]

Old John8-Feb-07 15:23

Old John

8-Feb-07 15:23

try this, but i havent test it.

dim fr as form1
if fr is nothing then
fr = new form1
end if

fr.show()

TwoFaced8-Feb-07 7:42

TwoFaced

8-Feb-07 7:42

Creating a single instance application just prevents an application from being run more then once. It doesn't prevent a form from being created multiple times. I believe the appropriate way to create a single instance form is the following.

Public Class Form2
    Private Shared m_Singleton As Form2     'Current instance

    'Declared private so a new instance can't be created directly
    Private Sub New()

        ' This call is required by the Windows Form Designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.
    End Sub

    'Gets the current instance of the form or passes back a new one
    Shared ReadOnly Property Instance() As Form2
        Get
            If m_Singleton Is Nothing OrElse _
                m_Singleton.IsDisposed OrElse _
                m_Singleton.Disposing Then m_Singleton = New Form2

            Return m_Singleton
        End Get
    End Property
End Class

However, if this is your main form you may need to make a small tweak. The code that gets generated to load your form won't used the shared property Instance. If you get an error and can't figure it out let me know. All I did was double clicked the error and then changed the line it brought me to so that it used the Instance property.

charchabil0310-Feb-07 5:51

10-Feb-07 5:51

thx for helping

I used your Code and

when i was calling the form with following code :

Dim frm As New frmCollectAlarms<br />
        frm.Show()

I got the following error

Error 1 'AMS.frmCollectAlarms.Private Sub New()' is not accessible in this context because it is 'Private'

any hint

Regards
Ramy

TwoFaced10-Feb-07 7:10

TwoFaced

10-Feb-07 7:10

Sorry, I should have mentioned how to use it also. The 'Sub New' was declared private so you can't create a new instance of the form. If you could create a new instance then you would be able to create multiple instances, which would defeat the purpose of a singleton form.

The proper way to access the form is through the shared property 'instance'. So to show the form you would just use

frmCollectAlarms.Instance.Show

If you create a variable to point to the form you would use

dim frm as frmCollectAlarms = frmCollectAlarms.Instance

However, that method isn't necessary and kind of goes around the idea of a singleton form. The reason is that you could technically have more then one frmCollectAlarms in memory, however, only one would be usefull while the others would be disposed.

One thing I learned is that the method I used isn't thread safe. I did a little research after I posted the code just to make sure I hadn't steered you wrong. If you plan on accessing the form from multiple threads then you should do a little research on creating a thread safe singleton form. However, if you don't plan on accessing it from multiple threads then I wouldn't worry about it. Although looking up singleton forms may be a good idea anyway just for future knowledge. Especially 'thread safe' singleton forms.

charchabil0310-Feb-07 21:16

item with same key has already been adding

10-Feb-07 21:16

i m not using threads...
i guess its working pretty good
thx for ur help Blush | :O

Regards
Ramy

Closing a form

jady848-Feb-07 5:51

jady84

8-Feb-07 5:51

Hi all,
Im trying to close aform by pressinga button, but the form doesnt seem to close (rather it just sits in my task bar below)

i have form1 open and by pressing a button i'd like form2 to close and form3 to open so heres my code.

Form2.Close()
Dim popup As New Form3
popup.Show()

but this doesnt seem to work (the button for this code is on form1)

Thanks in Advance

Jaidev

Re: Closing a form

M-Hall8-Feb-07 6:21

M-Hall

8-Feb-07 6:21

It looks like you are using the form itself not an instance of the form.
i.e
Public Class Form1
Inherits System.Windows.Forms.Form
Dim f As Windows.Forms.Form

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
f = New Form2
f.Show()
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
f.Close()

End Sub
End Class

charchabil038-Feb-07 5:32

8-Feb-07 5:32

Hello guys
an error occured while i was choosing a picture within a picture box
the error is :

item with same key has already been adding

I cant add an image to my project,not even background image for a form
I always get the above error

Note : if i open an other Project and try to add a picture,everything goes fine

Regards
Ramy

Christian Graus8-Feb-07 9:04

Christian Graus

8-Feb-07 9:04

That's a weird designer error. Have you tried adding the image in code instead ?

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog

charchabil0310-Feb-07 9:43

10-Feb-07 9:43

Coding went good

PictureBox1.Image = Image.FromFile("IMAGE_00098.jpg")

but i m still getting the same error as before ,if I m trying to add a picture not by coding

I think i have done sght in Resources things....
do u think that might cause such error?

Regards
Ramy

Christian Graus10-Feb-07 10:35

Christian Graus

10-Feb-07 10:35

I have no idea, sorry.

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog

charchabil0310-Feb-07 21:26