Threading with forms

  • Thread starter Thread starter John
  • Start date Start date
J

John

Hi

I am trying to create (not open) several forms in the background threads
using the code given below at the end.

1. Am I doing it correctly?

2. How can I get handle sot these forms in the calling sub so I can access
these forms after creation.

3. How do I know when threads have finished forms creation so I can show the
form if needed?

Thanks

Regards


Code
====

Private Sub Main()
Dim t1 As New Thread(AddressOf CreateForm)
t1.Start(GetType(Form1))

Dim t2 As New Thread(AddressOf CreateForm)
t2.Start(GetType(Form2))

Dim t3 As New Thread(AddressOf CreateForm)
t3.Start(GetType(Form3))
End Sub

Public Sub CreateForm(ByVal ft As Object)
Dim t As Type = TryCast(ft, Type)
If Not t Is Nothing Then
Using f As Form = TryCast(Activator.CreateInstance(t, False),
Form)
End Using
End If
End Sub
 
John,

Forms are not meant to be used as child threads.

A form is an UI which interact with a user, how would you let the user input
data assynchonosly, we have more fingers, but there is always only one form
active on your screen.

Be aware that multithreading cost more processing time then single trheading
as the threads need to be managed, therefore I don't see the sense in what
you try to do.

Cor
 
Hi

I am trying to create (not open) several forms in the background threads
using the code given below at the end.

1. Am I doing it correctly?

2. How can I get handle sot these forms in the calling sub so I can access
these forms after creation.

3. How do I know when threads have finished forms creation so I can show the
form if needed?

Thanks

Regards


Code
====

Private Sub Main()
Dim t1 As New Thread(AddressOf CreateForm)
t1.Start(GetType(Form1))

Dim t2 As New Thread(AddressOf CreateForm)
t2.Start(GetType(Form2))

Dim t3 As New Thread(AddressOf CreateForm)
t3.Start(GetType(Form3))
End Sub

Public Sub CreateForm(ByVal ft As Object)
Dim t As Type = TryCast(ft, Type)
If Not t Is Nothing Then
Using f As Form = TryCast(Activator.CreateInstance(t, False), Form)
Click to expand...

' Add this to show the form
Application.Run(f)
End Using
End If
End Sub
Click to expand...

Application.Run starts a new message pump on the current thread - and
shows the form. As for access to the forms after creation... Well, if
you intended to do that then you would need to increase the scope of you
form variables, and that would greatly increase the complexity of the
code. You would of course, have to make sure that all access to those
forms was marshaled correctly (using Invoke or BeginInvoke/EndInvoke) -
since as always, windows forms are NOT thread safe, and can not be
directly accessed from other threads.

Any logic on that thread would have to be in the form that is passed to
applciation.run, since it will not return until the form is closed - in
other words, it's a blocking method.

Can you explain exactly what you are trying to accomplish? There is
probably a simpler way of doing whatever it is your trying to do :)
 
John said:
I am trying to create (not open) several forms in the background threads
using the code given below at the end.
Click to expand...

I suggest to open all form's in the application's main (UI) thread and use
'Control.InvokeRequired', 'Control.BeginInvoke', and 'Control.Invoke' to
access the controls/forms from within the other threads.
 
I have several forms and clients are complaining that they are sick of time
that it takes to open one form after another. I was hoping that after first
form is loaded the rest can start loading in background without being
visible. That way when user needs them they are already loaded and become
visible quicker.

Thanks

Regards
 
John said:
I have several forms and clients are complaining that they are sick of time
that it takes to open one form after another. I was hoping that after
first form is loaded the rest can start loading in background without being
visible. That way when user needs them they are already loaded and become
visible quicker.
Click to expand...

Forms load is pretty fast. It's what you're doing during the form load that
can slow things down. And sometimes one has to give the illusion of speed by
not loading all the table rows into a datagrid but load a subset of data
during the form load and other things one can do to give the illusion of
speed.

http://msdn.microsoft.com/en-us/magazine/cc163630.aspx
 
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