Method Invoking and SyncLock?

[Vinny]

Hello!

My application at the moment is running on various threads. there is a point
where one of the threads wants to make add a node to a tree view, but it
wont let me because the thread where i want to change it is not the same as
the one that created it.

this all makes sense, i need to use the invoke method. the part that
confuses me is that i thought the "SyncLock" statement was for...

could someone kindly explain to me the difference?

also, i was trying to get it working with the Invoke method. But the problem
is this: how am i going to add a specific text to the tree view if the
delegate cannot take any parameters? will i have to make a class level
variable so that the invoked method and the original method can pass the
text of the tree node to each other?

once again, im confused!

thank you!

Vinny

[Rob Teixeira]

"Vinny" <vad@stgroup.net> wrote:
>Hello!
>
>My application at the moment is running on various threads. there is a point
>where one of the threads wants to make add a node to a tree view, but it
>wont let me because the thread where i want to change it is not the same
as
>the one that created it.

Yep

>this all makes sense, i need to use the invoke method. the part that
>confuses me is that i thought the "SyncLock" statement was for...
>
>could someone kindly explain to me the difference?

No. SyncLock is used to sync threads so they don't stomp on the same data
at the same time. When you create a synclock block, only threads that can
obtain the lock are allowed to execute and everyone else wanting to get in
has to wait.

The problem with multiple threads on WinForms is that the underlying window
message loop is controlled by the thread that created it. Only that thread
is allowed to muck with the messages (amoung other things). Since most of
the methods are really posting and peeking at the messages, this is why those
methods need to be run from the original thread.

>also, i was trying to get it working with the Invoke method. But the problem
>is this: how am i going to add a specific text to the tree view if the
>delegate cannot take any parameters? will i have to make a class level
>variable so that the invoked method and the original method can pass the
>text of the tree node to each other?

You have to create your own delegate for the node.add() method and pass that
delegate to the Invoke method.

Public Delegate Function AddNodeDelegate(ByVal text As String) As TreeNode

' then somewhere else in your code:

Sub DoThreadStuff()
If TreeView1.InvokeRequired Then
Dim MyDelegate As AddNodeDelegate = AddressOf TreeView1.Nodes.Add
TreeView1.Invoke(MyDelegate, New Object() {"Node1 Text"})
Else
TreeView1.Nodes.Add("Node1 Text")
End If
t.Abort()
End Sub

Notice that you pass parameters to the Delegate in the Invoke method by using
an object array. Also, I added the Abort line to terminate the thread in
that method. You obviously don't need to do that.


-Rob

[Vinny]

Hello Rob,

Yesterday night, as a "work around", i made an object called TreeUpdater.

what i do in my project is when i want to add a node to the tree view, i add
that text to a property of the my TreeUpdater object, then i pass in the
address of a method in the TreeUpdater object, like so:

Dim Updater as new TreeUpdater(TreeView)
Updater.Text = "NewNodeText"
TreeView.Invoke(New MethodInvoker(AddressOf Updater.AddNodeToTree))

and the AddNodeToTree Method looks like so:

Friend Sub AddUserToTree()
m_Tree.Nodes.Add(Me.Text)
End Sub

Well, thats my "work around" and it seemed to work just fine. Do you think
that my "WorkAround" is bad coding? or bad practice? or inefficient?
compared to your example?

thank you...

Vinny



"Rob Teixeira" <RobTeixeira@@msn.com> wrote in message
news:3ca347ba$1@10.1.10.29...
>
> "Vinny" <vad@stgroup.net> wrote:
> >Hello!
> >
> >My application at the moment is running on various threads. there is a
point
> >where one of the threads wants to make add a node to a tree view, but it
> >wont let me because the thread where i want to change it is not the same
> as
> >the one that created it.
>
> Yep
>
> >this all makes sense, i need to use the invoke method. the part that
> >confuses me is that i thought the "SyncLock" statement was for...
> >
> >could someone kindly explain to me the difference?
>
> No. SyncLock is used to sync threads so they don't stomp on the same data
> at the same time. When you create a synclock block, only threads that can
> obtain the lock are allowed to execute and everyone else wanting to get in
> has to wait.
>
> The problem with multiple threads on WinForms is that the underlying
window
> message loop is controlled by the thread that created it. Only that thread
> is allowed to muck with the messages (amoung other things). Since most of
> the methods are really posting and peeking at the messages, this is why
those
> methods need to be run from the original thread.
>
> >also, i was trying to get it working with the Invoke method. But the
problem
> >is this: how am i going to add a specific text to the tree view if the
> >delegate cannot take any parameters? will i have to make a class level
> >variable so that the invoked method and the original method can pass the
> >text of the tree node to each other?
>
> You have to create your own delegate for the node.add() method and pass
that
> delegate to the Invoke method.
>
> Public Delegate Function AddNodeDelegate(ByVal text As String) As TreeNode
>
> ' then somewhere else in your code:
>
> Sub DoThreadStuff()
> If TreeView1.InvokeRequired Then
> Dim MyDelegate As AddNodeDelegate = AddressOf
TreeView1.Nodes.Add
> TreeView1.Invoke(MyDelegate, New Object() {"Node1 Text"})
> Else
> TreeView1.Nodes.Add("Node1 Text")
> End If
> t.Abort()
> End Sub
>
> Notice that you pass parameters to the Delegate in the Invoke method by
using
> an object array. Also, I added the Abort line to terminate the thread in
> that method. You obviously don't need to do that.
>
>
> -Rob