Asynchronous problem

[bernardpace]

Hi,

I am using the following code

private void menuItemStart_C lick(object sender, System.EventArg s e)
{
DataTable tbRand, tbShow;
int randSize;

....
// schema of tbShow is being loaded from an xsd file
tbRand = DrawEngine.Gene rateAllDraws(tb Rand, randSize, ref tbShow);
dataGridRandomi zed.DataSource = tbShow;
....
}

This code works ok, and data is being showed correctly in datagrid.
Now I am trying to convert it to asynchronous code as shown below.

public delegate DataTable GeneratingAllDr awsDelegate(Dat aTable table,
int tot, ref DataTable show);

private void menuItemStart_C lick(object sender, System.EventArg s e)
{
...
GeneratingAllDr awsDelegate dc = new
GeneratingAllDr awsDelegate(Dra wEngine.Generat eAllDraws);
AsyncCallback cb = new AsyncCallback(g etResultAllDraw s);
IAsyncResult ar = dc.BeginInvoke( tbRand, randSize, ref tbShow, cb,
null);
...
}

private void getResultAllDra ws(IAsyncResult ar)
{
DataTable tbRand, tbShow;
GeneratingAllDr awsDelegate del;

// schema of tbShow is being loaded from an xsd file

del = (GeneratingAllD rawsDelegate) ((AsyncResult)a r).AsyncDelegat e;
tbRand = del.EndInvoke(r ef tbShow, ar);
dataGridRandomi zed.DataSource = tbShow;

}

When I execute this code, no data is being shown in datagrid(when
passing tbRand as DataSource same behaviour was given). I also tried
to place the tbShow into a DataSet and write the data to an XML file,
but no file is being created. Also no exception is being rised.

Can someone help me figure my problem out.
Thanks in Advance

[Richard Blewett [DevelopMentor]]

The problem is that the async callback is being executed on a worker thread not on the UI thread. When you set the datasource, the datagrid tries to update itself on the wrong thread. You need to ste the datasource on the UI thread by using dataGridRandomi zed.BeginInvoke and pass it a delegate that will be executed on the UI thread. One common way to do this is to re-use the async callback method like this:

private void getResultAllDra ws(IAsyncResult ar)
{
if( dataGridRandomi zed.InvokeRequi red )
{
dataGridRandomi zed.BeginInvoke (new AsyncCallback(g etResultAllDraw s), new object[]{ar});
}
else
{
DataTable tbRand, tbShow;
GeneratingAllDr awsDelegate del;

// schema of tbShow is being loaded from an xsd file

del = (GeneratingAllD rawsDelegate) ((AsyncResult)a r).AsyncDelegat e;
tbRand = del.EndInvoke(r ef tbShow, ar);
dataGridRandomi zed.DataSource = tbShow;
}
}

Regards

Richard Blewett - DevelopMentor
http://www.dotnetconsult.co.uk/weblog
http://www.dotnetconsult.co.uk

Hi,

I am using the following code

private void menuItemStart_C lick(object sender, System.EventArg s e)
{
DataTable tbRand, tbShow;
int randSize;

...
// schema of tbShow is being loaded from an xsd file
tbRand = DrawEngine.Gene rateAllDraws(tb Rand, randSize, ref tbShow);
dataGridRandomi zed.DataSource = tbShow;
...
}

This code works ok, and data is being showed correctly in datagrid.
Now I am trying to convert it to asynchronous code as shown below.

public delegate DataTable GeneratingAllDr awsDelegate(Dat aTable table,
int tot, ref DataTable show);

private void menuItemStart_C lick(object sender, System.EventArg s e)
{
...
GeneratingAllDr awsDelegate dc = new
GeneratingAllDr awsDelegate(Dra wEngine.Generat eAllDraws);
AsyncCallback cb = new AsyncCallback(g etResultAllDraw s);
IAsyncResult ar = dc.BeginInvoke( tbRand, randSize, ref tbShow, cb,
null);
...
}

private void getResultAllDra ws(IAsyncResult ar)
{
DataTable tbRand, tbShow;
GeneratingAllDr awsDelegate del;

// schema of tbShow is being loaded from an xsd file

del = (GeneratingAllD rawsDelegate) ((AsyncResult)a r).AsyncDelegat e;
tbRand = del.EndInvoke(r ef tbShow, ar);
dataGridRandomi zed.DataSource = tbShow;

}

When I execute this code, no data is being shown in datagrid(when
passing tbRand as DataSource same behaviour was given). I also tried
to place the tbShow into a DataSet and write the data to an XML file,
but no file is being created. Also no exception is being rised.

Can someone help me figure my problem out.
Thanks in Advance

[bernardpace]

Thanks for your help, problem has been solved successfully