FileSystemWatch er communication to Windows FORM

[Angelo]

Hi all,

I'm using a FileSystemWatch er to monitor a directory. I want the FSW
to pop up my already instantiated but invisible form.

However, I'm running into some problems with this.

1) In the FSW.Changed FileSystemEvent handler, I called the Show method
'frmMain.Show( )' on my form, the form appears but not completely
painted and it appears to be hanging with the hourglass.

private void OnCreated( )
{
frmMain.Show( );

//update the datasource, append to DataTable

}

2) Once I have my form fully painted and not hanging, I want the FSW
to continue communicating with the now visible form relaying
information about the incoming files. See, on the form I have a
DataGridView that has as its datasource a Datatable that is appended
to by the FSW in the OnChanged event above.

I have 2 main classes: FORM and MASTER. the FORM class is self
explanatory. The MASTER class inherits from the ApplicationCont ext
class. This is where the FSW is located. I do this to show the form
only when new files are detected by the FSW.
Anyone have any ideas or am able to shed some light on these
questions?

Any help is much appreciated.


public static void Main( )
{
Application.Run (new MASTER( ) );
}

public class MASTER : ApplicationCont ext
{
private System.IO.FileS ystemWatcher;
...
}

public class FORM : Form
{
public System.Data.Dat aTable dt;
...
}

[Peter Duniho]

On Sat, 02 Jun 2007 00:08:42 -0700, Angelo <an*******@gmai l.comwrote:

[...]
1) In the FSW.Changed FileSystemEvent handler, I called the Show method
'frmMain.Show( )' on my form, the form appears but not completely
painted and it appears to be hanging with the hourglass.

[...]
2) Once I have my form fully painted and not hanging, I want the FSW
to continue communicating with the now visible form relaying
information about the incoming files. See, on the form I have a
DataGridView that has as its datasource a Datatable that is appended
to by the FSW in the OnChanged event above.

[...]
Anyone have any ideas or am able to shed some light on these
questions?

It seems to me that the main issue is that when the FileSystemWatch er
events are raised, the event handler is executed on a different thread
from your main UI thread. You should be able to address this problem by
using Form.Invoke() to execute the Show() method on the main UI thread
rather than calling Show() directly.

Likewise, I don't think there should be any problem having the event
handler update the DataGridView on the form, other than the fact that
there too you need to make sure you use Form.Invoke() to execute whatever
code will actually update the DataGridView.

Pete

[Hakan Fatih YILDIRIM]

hi,
if you want FSW to communicate with the directory.you have to open the
form in different thread.. you can use backgroundworke r component for
this task or you can make some search about system.threadin g
namespace..
you must do multi-thread application and u make attention to the
access modifiers of the controls. for example you have to write
another form's control's text.this control's access modifier have to
be public..i hope this helps you.

[Peter Duniho]

On Sat, 02 Jun 2007 03:13:34 -0700, Hakan Fatih YILDIRIM
<hf*********@gm ail.comwrote:

if you want FSW to communicate with the directory.you have to open the
form in different thread.. you can use backgroundworke r component for
this task or you can make some search about system.threadin g
namespace..

I don't see how that will solve anything. The issue is that the FSW
raises the event on a thread different from that the form's message pump
is on. The FSW doesn't know which thread the form should be executing on,
and so it really doesn't matter which thread you put the form on, the FSW
isn't going to be able to raise the event on the form's thread.

you must do multi-thread application and u make attention to the
access modifiers of the controls.

I also don't see what access modifiers have to do with multi-threaded
code. It's my assertion that there's no need to create a new thread
anyway, but even if you did, access modifiers on the form's controls are a
completely separate issue.

for example you have to write
another form's control's text.this control's access modifier have to
be public..i hope this helps you.

It's true, if you have code outside a particular form that you want to
access that form's control directly, you have to change the access
modifier for that control so that it's public. But you have to do that
whether the code is executing on the same thread as the form or a
different one.

Furthermore, I would suggest that it is better to not expose a control on
a form in the general case, and rather to provide specific public methods
in the form to provide encapsulated access to the control. That way, only
the form itself has access to the control and doesn't have to worry about
some external code messing with the control in an undesirable way.

Pete

[Moty Michaely]

Hi,

You have to synchronize the event calling thread with the form's
thread (message pump thread). You can use the form's Invoke member
method to do so.

for instance:

....
void OnEvent()
{
if( frm.InvokeReuir ed )
frm.Invoke(new MethodInvoker(O nEvent));
else
frm.Text = "Event called...";
}
....

Hope this helps.
Moty

[Moty Michaely]

On Jun 2, 1:40 pm, Moty Michaely <Moty...@gmail. comwrote:

Hi,

You have to synchronize the event calling thread with the form's
thread (message pump thread). You can use the form's Invoke member
method to do so.

for instance:

...
void OnEvent()
{
if( frm.InvokeReuir ed )
frm.Invoke(new MethodInvoker(O nEvent));
else
frm.Text = "Event called...";}

...

Hope this helps.
Moty

Oops,

Just saw that Pete answered. Sorry.

Moty.

[Angelo]

Guys,

Thanks for all your responses so far.

I've tried several things unsuccessfully.

1) Peter and Moty, I've tried form.Invoke( ) but I get an exception
that

"{"Invoke or BeginInvoke cannot be called on a control until the
window handle has been created."}"

The form has already been instantiated FORM frm = new FORM( ); and
in the constructor I call the ForceCreate( ) method.

Seems like a catch 22, with the form having to be already visible to
invoke the visible method.

Any ideas what's going on here?

2) I've also tried using a delegate to call the show method but still
I get the Exception above.

<CODE>
public delegate void delVoid( );

public class FORM
{
private System.IO.FileS ystemWatcher FSW;

public FORM ( )
{
FSW = new FileSystemWatch er( ) ;

//FSW definition here
...
FSW.Created += new FileSystemEvent Handler
( FSW_Created ) ;
FSW.EnableRaisi ngEvents = true;
}

private void FSW_Created( )
{
delVoid deleg = new delVoid( this.ShowForm ) ;
deleg.Invoke( ) ;
//have also tried deleg.BeginInvo ke( null, null ) ;
}

private void ShowForm( )
{
this.Show( ) ;
}
}
</CODE>

On Jun 2, 2:08 am, Angelo <angelo...@gmai l.comwrote:

Hi all,

I'm using a FileSystemWatch er to monitor a directory. I want the FSW
to pop up my already instantiated but invisible form.

However, I'm running into some problems with this.

1) In the FSW.Changed FileSystemEvent handler, I called the Show method
'frmMain.Show( )' on my form, the form appears but not completely
painted and it appears to be hanging with the hourglass.

private void OnCreated( )
{
frmMain.Show( );

//update the datasource, append to DataTable

}

2) Once I have my form fully painted and not hanging, I want the FSW
to continue communicating with the now visible form relaying
information about the incoming files. See, on the form I have a
DataGridView that has as its datasource a Datatable that is appended
to by the FSW in the OnChanged event above.

I have 2 main classes: FORM and MASTER. the FORM class is self
explanatory. The MASTER class inherits from the ApplicationCont ext
class. This is where the FSW is located. I do this to show the form
only when new files are detected by the FSW.

Anyone have any ideas or am able to shed some light on these
questions?

Any help is much appreciated.

public static void Main( )
{
Application.Run (new MASTER( ) );

}

public class MASTER : ApplicationCont ext
{
private System.IO.FileS ystemWatcher;
...

}

public class FORM : Form
{
public System.Data.Dat aTable dt;
...

}- Hide quoted text -

- Show quoted text -

[Angelo]

***** CORRECTION TO THE MY LAST POST *****

I used the frm.CreateContr ol( ) method, not frm.ForceCreate ( ) that I
mentioned.

<CODE>

private void FSW_Created( )
{
this.Invoke( new MethodInvoker( this.ShowForm ) );
}

private void ShowForm( )
{
this.Show( ) ;
}

</CODE>

[Peter Duniho]

On Sat, 02 Jun 2007 10:12:12 -0700, Angelo <an*******@gmai l.comwrote:

1) Peter and Moty, I've tried form.Invoke( ) but I get an exception
that

"{"Invoke or BeginInvoke cannot be called on a control until the
window handle has been created."}"

The form has already been instantiated FORM frm = new FORM( ); and
in the constructor I call the ForceCreate( ) method.

Seems like a catch 22, with the form having to be already visible to
invoke the visible method.

Any ideas what's going on here?

No. Well, yes, but I admit I don't really understand why the form's
underlying window handle hasn't been created yet. I can't find any
mention of a ForceCreate() method, so I can't comment on what you are
doing there. It does seem like there should be a way to force the form to
be created fully upon instantiation, but "should be" and "is" are
sometimes a long way apart. :)

You may find that you have to use Invoke() on the main form instead of the
status form. The main form would then optionally call Show() on the
status form, as well as displaying whatever data you want shown. I
suppose one might consider this a better design anyway, since it shifts
management of the status form to the main form where the management of
your UI should be anyway.

For example (warning: uncompiled, untested code...for illustration
purposes only :) ):

class MainForm
{
private StatusForm _status;
private FileSystemWatch er _fsw;

void InitFSW()
{
_fsw = new FileSystemWatch er();

_fsw.Created += FSW_CreatedInvo ke;
}

void FSW_CreatedInvo ke(object sender, FileSystemEvent Args fsea)
{
Invoke(new FileSystemEvent Handler(FSW_Cre ated), new object[]
{sender, fsea});
}

void FSW_Created(obj ect sender, FileSystemEvent Args fsea)
{
if (_status == null)
{
_status = new StatusForm();
}

if (!_status.Visib le)
{
_status.Show();
}

_status.FSW_Cre ated(sender, fsea);
}
}

class StatusForm
{
void FSW_Created(obj ect sender, FileSystemEvent Args fsea)
{
// do your actual status updating here
}
}

2) I've also tried using a delegate to call the show method but still
I get the Exception above.

No surprise there. A delegate is just a way to call a method. It's sort
of like a function pointer. It doesn't affect whether you are in a state
in which Invoke() is allowed or not.

Pete

[Peter Duniho]

On Sat, 02 Jun 2007 10:26:10 -0700, Angelo <an*******@gmai l.comwrote:

***** CORRECTION TO THE MY LAST POST *****

I used the frm.CreateContr ol( ) method, not frm.ForceCreate ( ) that I
mentioned.

Ah. That. Well, you'll note in the docs:

CreateControl does not create a control handle
if the control's Visible property is false

So, before calling CreateControl() , you need to make sure you set the
Visible property to true.

I think it's possible that is sufficient to solve your problem, rather
than all the extra code I posted. :)

Pete