BeginInvoke with a property?

A

AMDRIT

Hello everyone,

How do I access a property from another thread in VB'05? Thanks

public class frmblah
inherits system.windows.forms.form

private mCount as integer

private property Count as integer
get
return mCount
end get
set (value as integer)
mCount = value
end set
end property

private sub updatecount
if me.InvokeRequired then
'
'???????
'
else
me.count += 1
end if
end sub

end class
 
B

Brian Henry

This is for .NET not VB Classic, you might want to try a classic VB group
instead
 
D

david

Hello everyone,

How do I access a property from another thread in VB'05? Thanks

public class frmblah
inherits system.windows.forms.form

private mCount as integer

private property Count as integer
get
return mCount
end get
set (value as integer)
mCount = value
end set
end property

private sub updatecount
if me.InvokeRequired then
'
'???????
'
else
me.count += 1
end if
end sub

end class
Click to expand...

You don't need to worry about InvokeRequired here, that's for accessing
UI components on the UI thread. For ordinary properties, even if they
are properties of a Form class, you can just set them from any thread
(watching out for thread contention of course).
 
A

AMDRIT

David,

Thanks for the response. The actual issue I am working through is a splash
screen.

I have a component library that has a base form and a splash screen form.
All my application forms derive from the custom form, which now has two
additional methods, (ShowWait, HideWait). These methods will be used
primarly for long running processes called by the custom form, however, the
derived form could make use of it as well.

In VB'03 is was working great, my problem is in VB'05. The splash screen is
supposed to fade in and out over time while it is displayed. I encountered
two issues from the conversion.

1. I do not have access to doevents. Since control libraries do not have
access to the My namespace, I have been exploring
Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase. I
haven't found a way to associate my ExecutingAssembly with my library.
Threading.Thread.Sleep doesn't seem to do the job, of cource that could be a
result of my second issue.

2. Accessing the splash screens form methods and properties cause:
a. System.Threading.ThreadAbortException
b. System.ArgumentException
c. System.InvalidOperationException
d. System.Transactions Critical at
System.Windows.Forms.Control.SetVisibleCore(Boolean value)

What I have going on is a do...while loop that is calling the fade routine
when the splash screen is visible.

public sub DoFading
do while not done
call Fade
loop

me.hide()
me.close()

end sub

private sub Fade

dim fadedirection as fadetypes

if me.opacity <= 0 then
fadedirection = fadetypes.up
elseif me.opacity >= 1 then
fadedirection = fadetypes.down
end if

select case fadedirection
case fadetypes.up
me.opacity += pintStepping
case else
me.opacity -= pintStepping
end select

end sub

I changed my call to fade to Me.Invoke(New
Windows.Forms.MethodInvoker(AddressOf Fade))

as well as the logic to hide and close the form

I don't know what I am doing wrong, but it is not behaving like it used to.
 
H

Herfried K. Wagner [MVP]

Brian Henry said:
This is for .NET not VB Classic, you might want to try a classic VB group
instead
Click to expand...

Mhm... The question is clearly related to VB.NET.
 
D

david

David,

Thanks for the response. The actual issue I am working through is a splash
screen.

I have a component library that has a base form and a splash screen form.
All my application forms derive from the custom form, which now has two
additional methods, (ShowWait, HideWait). These methods will be used
primarly for long running processes called by the custom form, however, the
derived form could make use of it as well.

In VB'03 is was working great, my problem is in VB'05. The splash screen is
supposed to fade in and out over time while it is displayed. I encountered
two issues from the conversion.
Click to expand...

VB05 is a bit more persnickety about calling UI components from the
wrong thread.
1. I do not have access to doevents. Since control libraries do not have
access to the My namespace, I have been exploring
Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase. I
haven't found a way to associate my ExecutingAssembly with my library.
Click to expand...

I'm not sure why you need doEvents here, but it can be found at
System.Windows.Forms.Application.DoEvents().

Of course, it needs to be called from the UI thread.

Threading.Thread.Sleep doesn't seem to do the job, of cource that could be a
result of my second issue.

2. Accessing the splash screens form methods and properties cause:
a. System.Threading.ThreadAbortException
b. System.ArgumentException
c. System.InvalidOperationException
d. System.Transactions Critical at
System.Windows.Forms.Control.SetVisibleCore(Boolean value)

What I have going on is a do...while loop that is calling the fade routine
when the splash screen is visible.
Click to expand...

Seems like a timer would be more appropriate. In fact, the Forms.Timer
component will even handle calling you on the correct thread.
public sub DoFading
do while not done
call Fade
loop

me.hide()
me.close()

end sub

private sub Fade

dim fadedirection as fadetypes

if me.opacity <= 0 then
fadedirection = fadetypes.up
elseif me.opacity >= 1 then
fadedirection = fadetypes.down
end if

select case fadedirection
case fadetypes.up
me.opacity += pintStepping
case else
me.opacity -= pintStepping
end select

end sub

I changed my call to fade to Me.Invoke(New
Windows.Forms.MethodInvoker(AddressOf Fade))

as well as the logic to hide and close the form

I don't know what I am doing wrong, but it is not behaving like it used to.
Click to expand...

It's hard to tell from this snippet. I'm not even sure the threading is
the error here is from the UI thread issues (usually you get an
InvalidOperationException when that happens). One trick I like to do
for these types of problems is have the form methods handle their own
invoke requirements, like...


Private Sub Fade()
If Me.InvokeRequired Then
Me.Invoke(New MethodInvoker(AddressOf Fade))
Exit Sub
End If
' Do the real work
 
C

Chris Chilvers

1. I do not have access to doevents.
Click to expand...

You don't need it if your fade code is running on a thread you've created.

2. Accessing the splash screens form methods and properties cause:
a. System.Threading.ThreadAbortException
b. System.ArgumentException
c. System.InvalidOperationException
d. System.Transactions Critical at
System.Windows.Forms.Control.SetVisibleCore(Boolean value)

What I have going on is a do...while loop that is calling the fade routine
when the splash screen is visible.

public sub DoFading
do while not done
Me.Invoke(New Windows.Forms.MethodInvoker(AddressOf Fade))
loop

me.hide()
me.close()

end sub
Click to expand...

If you look at that code (assuming you've wrapped that call to Fade() inside of an invoke like you described) you will
see that your calls to hide() and close() are not using a MethodInvoker. These calls need to be executed from the
controls thread and will need to be invoked as well:

public sub DoFading
MethodInvoker fader = New MethodInvoker(AddressOf Fade)

do while not done
Me.Invoke(fader)
'Really should think about a sleep here so as not to eat cpu time
loop

Me.Invoke(New MethodInvoker(AddressOf Close())
end sub

This is making the assumption you have launched DoFading on a new thread, which it seems like you have done.
 

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