Problem passing dataset between worker and UI thread

C

Carl Heller

Working in VS2003, .Net 1.1

I'm working on a project where I compare data between two databases. This
is a lengthy process, and very data intensive, so I decided to create a
class, and thread out the work.

The order of work is as follows:
1. Retrieve the data from primary data source
2. Update UI with retrieved data - this is accomplished by passing a
dataset as an event parameter
3. Compare retrieved data to a secondary data source, updating UI
occasionally.

I'm running into 1 problem, and one weirdness, and I'm hoping someone can
guide me where I went wrong.

Problem: After data is bound to the datagrid and the compare to the
secondary data source is going on, if I scroll through the datagrid I get an
exception "Object reference not set to an instance of an object, and the
datagrid disappears, replaced by a big red X. StackTrace:

System.NullReferenceException: Object reference not set to an instance of an
object.
at System.Data.DataColumnPropertyDescriptor.GetValue(Object component)
at
System.Windows.Forms.DataGridColumnStyle.GetColumnValueAtRow(CurrencyManager
source, Int32 rowNum)
at System.Windows.Forms.DataGridTextBoxColumn.Paint(Graphics g, Rectangle
bounds, CurrencyManager source, Int32 rowNum, Brush backBrush, Brush
foreBrush, Boolean alignToRight)
at
System.Windows.Forms.DataGridRelationshipRow.PaintCellContents(Graphics g,
Rectangle cellBounds, DataGridColumnStyle column, Brush backBr, Brush
foreBrush, Boolean alignToRight)
at System.Windows.Forms.DataGridRow.PaintData(Graphics g, Rectangle
bounds, Int32 firstVisibleColumn, Int32 columnCount, Boolean alignToRight)
at System.Windows.Forms.DataGridRelationshipRow.Paint(Graphics g,
Rectangle bounds, Rectangle trueRowBounds, Int32 firstVisibleColumn, Int32
numVisibleColumns, Boolean alignToRight)
at System.Windows.Forms.DataGrid.PaintRows(Graphics g, Rectangle&
boundingRect)
at System.Windows.Forms.DataGrid.PaintGrid(Graphics g, Rectangle
gridBounds)
at System.Windows.Forms.DataGrid.OnPaint(PaintEventArgs pe)
at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e,
Int16 layer, Boolean disposeEventArgs)
at System.Windows.Forms.Control.WmPaint(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg,
IntPtr wparam, IntPtr lparam)

Weirdness:
While the compare to the secondary data source is going on, the thread's
dataset is being updated. But for some reason, the UI's dataset is being
updated as well. I thought that the UI would be working with a copy of the
thread's dataset when I do the BeginInvoke and create a new object, but it
obviously isn't. I have a feeling that my two issues are related, but I do
not have enough experience with threads to solve this.

I've provided a snip of the code so that you can understand how I'm making
the calls. If there is a better (more proper?) way of doing what I'm doing,
please educate me.

public class Verification //This is the class used by the worker thread
{
<snip>
private Verify()
{
dsVerification dsRetrievedData;

dsRetrievedData = RetrieveData();
DataUpdatedEvent (this, new StatusEventArgs(dsRetrievedData);
CompareToSecondary(dsRetrievedData);
}

<snip>

public delegate void DataUpdated(object sender, StatusEventArgs e);
public event DataUpdated DataUpdatedEvent;

} //End of Verification Class

private DataGrid dataGridVerification;
private Verifiy ioVerification;
private Thread ioThread;

private delegate void DataUpdatedDelegate(dsVerification adsRetrievedData);
private void DataUpdated (dsVerification adsRetrievedData)
{
dataGridVerification.DataSource = adsData.VerificationData;
}

private void ioVerification_DataUpdatedEvent(object sender, StatusEventArgs
e)
{
if (this.InvokeRequired)
{
this.BeginInvoke(new DataUpdatedDelegate(DataUpdated), new object[]
{e.Data});
return;
}

DataUpdated(e.Data);
}
 
C

Cor Ligthert [MVP]

Carl,

Before we look to your problem, why such a difficult method. Normally it is
just getting the public or better internal properties from your dataset
class?

In my idea is what you are doing the standard way.

Cor

Carl Heller said:
Working in VS2003, .Net 1.1

I'm working on a project where I compare data between two databases. This
is a lengthy process, and very data intensive, so I decided to create a
class, and thread out the work.

The order of work is as follows:
1. Retrieve the data from primary data source
2. Update UI with retrieved data - this is accomplished by passing a
dataset as an event parameter
3. Compare retrieved data to a secondary data source, updating UI
occasionally.

I'm running into 1 problem, and one weirdness, and I'm hoping someone can
guide me where I went wrong.

Problem: After data is bound to the datagrid and the compare to the
secondary data source is going on, if I scroll through the datagrid I get
an exception "Object reference not set to an instance of an object, and
the datagrid disappears, replaced by a big red X. StackTrace:

System.NullReferenceException: Object reference not set to an instance of
an object.
at System.Data.DataColumnPropertyDescriptor.GetValue(Object component)
at
System.Windows.Forms.DataGridColumnStyle.GetColumnValueAtRow(CurrencyManager
source, Int32 rowNum)
at System.Windows.Forms.DataGridTextBoxColumn.Paint(Graphics g,
Rectangle bounds, CurrencyManager source, Int32 rowNum, Brush backBrush,
Brush foreBrush, Boolean alignToRight)
at
System.Windows.Forms.DataGridRelationshipRow.PaintCellContents(Graphics g,
Rectangle cellBounds, DataGridColumnStyle column, Brush backBr, Brush
foreBrush, Boolean alignToRight)
at System.Windows.Forms.DataGridRow.PaintData(Graphics g, Rectangle
bounds, Int32 firstVisibleColumn, Int32 columnCount, Boolean alignToRight)
at System.Windows.Forms.DataGridRelationshipRow.Paint(Graphics g,
Rectangle bounds, Rectangle trueRowBounds, Int32 firstVisibleColumn, Int32
numVisibleColumns, Boolean alignToRight)
at System.Windows.Forms.DataGrid.PaintRows(Graphics g, Rectangle&
boundingRect)
at System.Windows.Forms.DataGrid.PaintGrid(Graphics g, Rectangle
gridBounds)
at System.Windows.Forms.DataGrid.OnPaint(PaintEventArgs pe)
at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e,
Int16 layer, Boolean disposeEventArgs)
at System.Windows.Forms.Control.WmPaint(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg,
IntPtr wparam, IntPtr lparam)

Weirdness:
While the compare to the secondary data source is going on, the thread's
dataset is being updated. But for some reason, the UI's dataset is being
updated as well. I thought that the UI would be working with a copy of
the thread's dataset when I do the BeginInvoke and create a new object,
but it obviously isn't. I have a feeling that my two issues are related,
but I do not have enough experience with threads to solve this.

I've provided a snip of the code so that you can understand how I'm making
the calls. If there is a better (more proper?) way of doing what I'm
doing, please educate me.

public class Verification //This is the class used by the worker thread
{
<snip>
private Verify()
{
dsVerification dsRetrievedData;

dsRetrievedData = RetrieveData();
DataUpdatedEvent (this, new StatusEventArgs(dsRetrievedData);
CompareToSecondary(dsRetrievedData);
}

<snip>

public delegate void DataUpdated(object sender, StatusEventArgs e);
public event DataUpdated DataUpdatedEvent;

} //End of Verification Class

private DataGrid dataGridVerification;
private Verifiy ioVerification;
private Thread ioThread;

private delegate void DataUpdatedDelegate(dsVerification
adsRetrievedData);
private void DataUpdated (dsVerification adsRetrievedData)
{
dataGridVerification.DataSource = adsData.VerificationData;
}

private void ioVerification_DataUpdatedEvent(object sender,
StatusEventArgs e)
{
if (this.InvokeRequired)
{
this.BeginInvoke(new DataUpdatedDelegate(DataUpdated), new object[]
{e.Data});
return;
}

DataUpdated(e.Data);
}
Click to expand...
 
C

Carl Heller

There was no good reason. I changed my code so that the dataset is public.
I use the event to notify the UI thread that the dataset has changed. Upon
testing, I still have the same issues.

Any other ideas?

Thanks,

Carl.


Cor Ligthert said:
Carl,

Before we look to your problem, why such a difficult method. Normally it
is just getting the public or better internal properties from your dataset
class?

In my idea is what you are doing the standard way.

Cor

Carl Heller said:
Working in VS2003, .Net 1.1

I'm working on a project where I compare data between two databases.
This is a lengthy process, and very data intensive, so I decided to
create a class, and thread out the work.

The order of work is as follows:
1. Retrieve the data from primary data source
2. Update UI with retrieved data - this is accomplished by passing a
dataset as an event parameter
3. Compare retrieved data to a secondary data source, updating UI
occasionally.

I'm running into 1 problem, and one weirdness, and I'm hoping someone can
guide me where I went wrong.

Problem: After data is bound to the datagrid and the compare to the
secondary data source is going on, if I scroll through the datagrid I get
an exception "Object reference not set to an instance of an object, and
the datagrid disappears, replaced by a big red X. StackTrace:

System.NullReferenceException: Object reference not set to an instance of
an object.
at System.Data.DataColumnPropertyDescriptor.GetValue(Object component)
at
System.Windows.Forms.DataGridColumnStyle.GetColumnValueAtRow(CurrencyManager
source, Int32 rowNum)
at System.Windows.Forms.DataGridTextBoxColumn.Paint(Graphics g,
Rectangle bounds, CurrencyManager source, Int32 rowNum, Brush backBrush,
Brush foreBrush, Boolean alignToRight)
at
System.Windows.Forms.DataGridRelationshipRow.PaintCellContents(Graphics
g, Rectangle cellBounds, DataGridColumnStyle column, Brush backBr, Brush
foreBrush, Boolean alignToRight)
at System.Windows.Forms.DataGridRow.PaintData(Graphics g, Rectangle
bounds, Int32 firstVisibleColumn, Int32 columnCount, Boolean
alignToRight)
at System.Windows.Forms.DataGridRelationshipRow.Paint(Graphics g,
Rectangle bounds, Rectangle trueRowBounds, Int32 firstVisibleColumn,
Int32 numVisibleColumns, Boolean alignToRight)
at System.Windows.Forms.DataGrid.PaintRows(Graphics g, Rectangle&
boundingRect)
at System.Windows.Forms.DataGrid.PaintGrid(Graphics g, Rectangle
gridBounds)
at System.Windows.Forms.DataGrid.OnPaint(PaintEventArgs pe)
at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs
e, Int16 layer, Boolean disposeEventArgs)
at System.Windows.Forms.Control.WmPaint(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg,
IntPtr wparam, IntPtr lparam)

Weirdness:
While the compare to the secondary data source is going on, the thread's
dataset is being updated. But for some reason, the UI's dataset is being
updated as well. I thought that the UI would be working with a copy of
the thread's dataset when I do the BeginInvoke and create a new object,
but it obviously isn't. I have a feeling that my two issues are related,
but I do not have enough experience with threads to solve this.

I've provided a snip of the code so that you can understand how I'm
making the calls. If there is a better (more proper?) way of doing what
I'm doing, please educate me.

public class Verification //This is the class used by the worker thread
{
<snip>
private Verify()
{
dsVerification dsRetrievedData;

dsRetrievedData = RetrieveData();
DataUpdatedEvent (this, new StatusEventArgs(dsRetrievedData);
CompareToSecondary(dsRetrievedData);
}

<snip>

public delegate void DataUpdated(object sender, StatusEventArgs e);
public event DataUpdated DataUpdatedEvent;

} //End of Verification Class

private DataGrid dataGridVerification;
private Verifiy ioVerification;
private Thread ioThread;

private delegate void DataUpdatedDelegate(dsVerification
adsRetrievedData);
private void DataUpdated (dsVerification adsRetrievedData)
{
dataGridVerification.DataSource = adsData.VerificationData;
}

private void ioVerification_DataUpdatedEvent(object sender,
StatusEventArgs e)
{
if (this.InvokeRequired)
{
this.BeginInvoke(new DataUpdatedDelegate(DataUpdated), new object[]
{e.Data});
return;
}

DataUpdated(e.Data);
}
Click to expand...
Click to expand...
 

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