Threading...

[Simon Verona]

I think I'm doing this wrong :

I have a class with a public shared method such as follows:

public shared sub myFunction
dim frm as new myFrm
dim t as new Threading.Threa d(Addressof myFrm.myShowDia log
t.start
end sub

In the frm - the myShowDialog just does a "me.showdialog" .

The idea is that this function will display a form, but then return control
back to the calling routine immediately without waiting for the form to be
closed.

It works, but I've had several reports of the form that is displayed
"crashing" as it is being displayed, with random errors (I've not got a
sample) or the whole application just disappearing (without error).

Can anybody assist, either by confirming or otherwise that what I'm doing is
reasonable, or perhaps letting me know a better way.

Regards
Simon

ps Previously posted by mistake to vb.controls group.

--
=============== =============== ==
Simon Verona
Dealer Management Service Ltd
Stewart House
Centurion Business Park
Julian Way
Sheffield
S9 1GD

Tel: [phone]
Fax: [phone]

--
=============== =============== ==
Simon Verona
Dealer Management Service Ltd
Stewart House
Centurion Business Park
Julian Way
Sheffield
S9 1GD

Tel: [phone]
Fax: [phone]

[iwdu15]

well im kinda curious on why it looks like your attempting to show another
form on a different thread....are you meaning to put the form on another
thread, and if so why?
--
-iwdu15

[Larry Lard]

Simon Verona wrote:

I think I'm doing this wrong :

I have a class with a public shared method such as follows:

public shared sub myFunction
dim frm as new myFrm
dim t as new Threading.Threa d(Addressof myFrm.myShowDia log
t.start
end sub

In the frm - the myShowDialog just does a "me.showdialog" .

The idea is that this function will display a form, but then return control
back to the calling routine immediately without waiting for the form to be
closed.

If this is what you want, why not just .Show (rather than .ShowDialog)
the form? Anyway...

>
It works, but I've had several reports of the form that is displayed
"crashing" as it is being displayed, with random errors (I've not got a
sample) or the whole application just disappearing (without error).

Can anybody assist, either by confirming or otherwise that what I'm doing is
reasonable, or perhaps letting me know a better way.

I think you are falling foul of the rule whereby UI elements cannot be
safely interacted with from threads other than their 'owning' thread -
that on which they are created. So here the myFrm is created on the
thread that enters this procedure, but then passed to a different
thread to show itself. Thus this second thread will be accessing UI
elements it didn't create -bad.

The fix (if there are deeper reasons why you need to do this sort of
thing) is to move the form creation from before thread-creation to
after it. That is, at the moment you are saying:

Create form
Create thread (giving it the form)
Start thread - thread goes on to show form

Instead you should say

Create thread
Start thread - thread goes on to create form, then show it.

Probably the logical place for this new routine would be a Shared
procedure in myFrm:

Public Shared Sub NewShowDialog
Dim f As New myFrm
f.ShowDialog
End Sub

then replace your current myFunction with

Dim t As New Thread(AddressO f myFrm.NewShowDi alog)
t.Start

But please first consider my first question about .Show vs
..ShowDialog...

--
Larry Lard
Replies to group please
When starting a new topic, please mention which version of VB/C# you
are using

[Simon Verona]

Good question...

Maybe if I explain the application....

I have a main form, which displays a list of entries. The application
allows you to click on an entry to open a form to view/update the details of
that entry.

However, I wanted to allow multiple entries to be displayed together.

Also, I wanted to encapsulate the display of the form within a class (it is
used in many parts of the application as well, so I felt it would be
easier).

If I display the form without creating the thread, the form dies as soon as
the subroutine exits back to the main form (IIRC!), so I came up with this
as a workaround. It also seemed to have the affect of making the
application seem to run smoother (though that could just be me). If I don't
create the thread and just use showdialog, then the original form is blocked
until it returns.

I don't know why it should be causing a problem, but if there is a better
way of acheiving the same thing without creating the thread then I'm up for
it!

Regards
Simon

--
=============== =============== ==
Simon Verona
Dealer Management Service Ltd
Stewart House
Centurion Business Park
Julian Way
Sheffield
S9 1GD

Tel: [phone]
Fax: [phone]

"iwdu15" <jmmgoalsteraty ahoodotcomwrote in message
news:C1******** *************** ***********@mic rosoft.com...

well im kinda curious on why it looks like your attempting to show another
form on a different thread....are you meaning to put the form on another
thread, and if so why?
--
-iwdu15

[Simon Verona]

See my previous reply, I've had problem with the form disappearing when the
subroutine exits... (I'm presuming the object is killed on exit?)

I understand what you are saying about the frm creation and use being on
seperate threads. I must admit to not thinking of having a shared entry on
the form to display itself!

Regards
Simon

--
=============== =============== ==
Simon Verona
Dealer Management Service Ltd
Stewart House
Centurion Business Park
Julian Way
Sheffield
S9 1GD

Tel: [phone]
Fax: [phone]

"Larry Lard" <la*******@hotm ail.comwrote in message
news:11******** *************@m 73g2000cwd.goog legroups.com...

>
Simon Verona wrote:

>I think I'm doing this wrong :

I have a class with a public shared method such as follows:

public shared sub myFunction
dim frm as new myFrm
dim t as new Threading.Threa d(Addressof myFrm.myShowDia log
t.start
end sub

In the frm - the myShowDialog just does a "me.showdialog" .

The idea is that this function will display a form, but then return
control
back to the calling routine immediately without waiting for the form to
be
closed.

If this is what you want, why not just .Show (rather than .ShowDialog)
the form? Anyway...

>>
It works, but I've had several reports of the form that is displayed
"crashing" as it is being displayed, with random errors (I've not got a
sample) or the whole application just disappearing (without error).

Can anybody assist, either by confirming or otherwise that what I'm doing
is
reasonable, or perhaps letting me know a better way.

I think you are falling foul of the rule whereby UI elements cannot be
safely interacted with from threads other than their 'owning' thread -
that on which they are created. So here the myFrm is created on the
thread that enters this procedure, but then passed to a different
thread to show itself. Thus this second thread will be accessing UI
elements it didn't create -bad.

The fix (if there are deeper reasons why you need to do this sort of
thing) is to move the form creation from before thread-creation to
after it. That is, at the moment you are saying:

Create form
Create thread (giving it the form)
Start thread - thread goes on to show form

Instead you should say

Create thread
Start thread - thread goes on to create form, then show it.

Probably the logical place for this new routine would be a Shared
procedure in myFrm:

Public Shared Sub NewShowDialog
Dim f As New myFrm
f.ShowDialog
End Sub

then replace your current myFunction with

Dim t As New Thread(AddressO f myFrm.NewShowDi alog)
t.Start

But please first consider my first question about .Show vs
.ShowDialog...

--
Larry Lard
Replies to group please
When starting a new topic, please mention which version of VB/C# you
are using

[iwdu15]

if you want to show a new form on a different thread, then the new thread
must then create the form object:

Private Delegate Sub delNewThread

Private Sub btnNewThread_Cl ick(...)

Dim x as New delNewThread(Ad dressOf CreateNewFormTh readBegin)

Me.Invoke(x)

End Sub

Private Sub CreateNewFormTh readBegin()

Dim frm as New Form2

frm.ShowDialog( )

End Sub
that will create a new form on a different thread then show it
--
-iwdu15

[iwdu15]

well, if you wan to do it that way, then make sure our thread safe. Threads
can only access objects they create, for instance your Form1 cannot access
things on your other thread's form and vice versa, keep that in mind. To
access methods on other threads, use the threads Invoke method, dont call the
method directly. Keeping that in mind, there wouldnt be a need to call
"ShowDialog " and show the form on a new thread....i dont know if that would
cause issues or not, so your best bet would be calling "Show", not
"ShowDialog "
--
-iwdu15

[Simon Verona]

Larry

I had a go at implementing your thought, but of course, the "real" code is
not quite as simple as the example I posted:

The real code passes a variable through to the form when constructing ie

dim frm as new myfrm(myvar)
dim t as new threading.threa d(addressof frm.myShowDialo g)
t.start

I can't work out how to create a shared function that I can call on another
thread AND pass a parameter!

Regards
Simon

--
=============== =============== ==
Simon Verona
Dealer Management Service Ltd
Stewart House
Centurion Business Park
Julian Way
Sheffield
S9 1GD

Tel: [phone]
Fax: [phone]

"Larry Lard" <la*******@hotm ail.comwrote in message
news:11******** *************@m 73g2000cwd.goog legroups.com...

>
Simon Verona wrote:

>I think I'm doing this wrong :

I have a class with a public shared method such as follows:

public shared sub myFunction
dim frm as new myFrm
dim t as new Threading.Threa d(Addressof myFrm.myShowDia log
t.start
end sub

In the frm - the myShowDialog just does a "me.showdialog" .

The idea is that this function will display a form, but then return
control
back to the calling routine immediately without waiting for the form to
be
closed.

If this is what you want, why not just .Show (rather than .ShowDialog)
the form? Anyway...

>>
It works, but I've had several reports of the form that is displayed
"crashing" as it is being displayed, with random errors (I've not got a
sample) or the whole application just disappearing (without error).

Can anybody assist, either by confirming or otherwise that what I'm doing
is
reasonable, or perhaps letting me know a better way.

I think you are falling foul of the rule whereby UI elements cannot be
safely interacted with from threads other than their 'owning' thread -
that on which they are created. So here the myFrm is created on the
thread that enters this procedure, but then passed to a different
thread to show itself. Thus this second thread will be accessing UI
elements it didn't create -bad.

The fix (if there are deeper reasons why you need to do this sort of
thing) is to move the form creation from before thread-creation to
after it. That is, at the moment you are saying:

Create form
Create thread (giving it the form)
Start thread - thread goes on to show form

Instead you should say

Create thread
Start thread - thread goes on to create form, then show it.

Probably the logical place for this new routine would be a Shared
procedure in myFrm:

Public Shared Sub NewShowDialog
Dim f As New myFrm
f.ShowDialog
End Sub

then replace your current myFunction with

Dim t As New Thread(AddressO f myFrm.NewShowDi alog)
t.Start

But please first consider my first question about .Show vs
.ShowDialog...

--
Larry Lard
Replies to group please
When starting a new topic, please mention which version of VB/C# you
are using

[iwdu15]

look at my code example above
--
-iwdu15

[Simon Verona]

Thanks for the example...

However, I'm not 100% positive how I would modify your example to pass a
variable to the form.

I presume that I can't set a local private variable (declared outside of ay
subroutines) and then access it from within the CreateNewFormTh readBegin
sub? I'm presuming that can I can't directly pass any variables directly
through to the CreateNewFromTh readBegin (ie modifying it to Private Sub
CreateNewFromTh readBegin(myvar as string) )

Apologies if I've missed the obvious - Can I use the facts that it's 5pm and
very hot to mitigate my stupidity? <G>

Thanks
Simon

--
=============== =============== ==
Simon Verona
Dealer Management Service Ltd
Stewart House
Centurion Business Park
Julian Way
Sheffield
S9 1GD

Tel: [phone]
Fax: [phone]

"iwdu15" <jmmgoalsteraty ahoodotcomwrote in message
news:D6******** *************** ***********@mic rosoft.com...

look at my code example above
--
-iwdu15