background data retrieval

[Doug Bell]

Hi,
I have an application that has a "Data Access Class" and "User Interface
Class".

It is for receiving Purchase Order data from one system and pushing
processed transactions to another system.

The system generally works quite well.
Currently the User interface calls for a refresh of data every 15 minutes
(selectable) and the Data Access Class connects to the DB and retrieves the
data structured to suit the application. During the retrieval it displays
messages informing the User of the various downloads. Each application has
its own Data Access Class. It takes between 30 seconds and 5 minutes to
refresh the data dependant on where the User is located

I have been asked to make the refresh transparent so that the User does not
have to wait for the Data Access Layer to get its data as some site have a
very slow connections to the network.

I am not sure how to achieve this new requirement.
I thought that I could make the Data Access Class a separate application
that loads with the User interface and then periodically retrieves the data
and saves it into a local database file (mdb ?) rather than into the current
Data Set and then have the User Interface asynchronously connect to the
local database and update its records.

I would appreciate any oppinions.

Regards

Doug

[Beth Massi [Architect MVP]]

Hi Doug,

You can execute the loading of your data on a separate thread so that the
form is still responsive to the user, however, you need to be careful that
none of the UI elements work with that data before the data is retrieved.
Once the data is loaded, your data access class should raise an event that
you can handle so you can call the invoke method to marshal the call to the
UI thread. Here's the basic idea (note- this example uses the SQL northwind
database):

Public Class Form1
Inherits System.Windows. Forms.Form

#Region " Windows Form Designer generated code "

Public Sub New()
MyBase.New()

'This call is required by the Windows Form Designer.
InitializeCompo nent()

'Add any initialization after the InitializeCompo nent() call

End Sub

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Disp ose()
End If
End If
MyBase.Dispose( disposing)
End Sub

'Required by the Windows Form Designer
Private components As System.Componen tModel.IContain er

'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
Friend WithEvents DataGrid1 As System.Windows. Forms.DataGrid
Friend WithEvents TextBox1 As System.Windows. Forms.TextBox
Friend WithEvents Button1 As System.Windows. Forms.Button
Friend WithEvents TextBox2 As System.Windows. Forms.TextBox
Friend WithEvents Button2 As System.Windows. Forms.Button
Friend WithEvents Button3 As System.Windows. Forms.Button
Friend WithEvents Button4 As System.Windows. Forms.Button
Friend WithEvents Button5 As System.Windows. Forms.Button
Friend WithEvents CheckBox1 As System.Windows. Forms.CheckBox
<System.Diagnos tics.DebuggerSt epThrough()> Private Sub
InitializeCompo nent()
Me.DataGrid1 = New System.Windows. Forms.DataGrid
Me.TextBox1 = New System.Windows. Forms.TextBox
Me.Button1 = New System.Windows. Forms.Button
Me.TextBox2 = New System.Windows. Forms.TextBox
Me.Button2 = New System.Windows. Forms.Button
Me.Button3 = New System.Windows. Forms.Button
Me.Button4 = New System.Windows. Forms.Button
Me.Button5 = New System.Windows. Forms.Button
Me.CheckBox1 = New System.Windows. Forms.CheckBox
CType(Me.DataGr id1, System.Componen tModel.ISupport Initialize).Beg inInit()
Me.SuspendLayou t()
'
'DataGrid1
'
Me.DataGrid1.An chor = CType((((System .Windows.Forms. AnchorStyles.To p Or
System.Windows. Forms.AnchorSty les.Bottom) _
Or System.Windows. Forms.AnchorSty les.Left) _
Or System.Windows. Forms.AnchorSty les.Right),
System.Windows. Forms.AnchorSty les)
Me.DataGrid1.Da taMember = ""
Me.DataGrid1.He aderForeColor = System.Drawing. SystemColors.Co ntrolText
Me.DataGrid1.Lo cation = New System.Drawing. Point(16, 120)
Me.DataGrid1.Na me = "DataGrid1"
Me.DataGrid1.Si ze = New System.Drawing. Size(472, 208)
Me.DataGrid1.Ta bIndex = 0
'
'TextBox1
'
Me.TextBox1.Loc ation = New System.Drawing. Point(24, 56)
Me.TextBox1.Nam e = "TextBox1"
Me.TextBox1.Siz e = New System.Drawing. Size(48, 20)
Me.TextBox1.Tab Index = 1
Me.TextBox1.Tex t = "TextBox1"
'
'Button1
'
Me.Button1.Loca tion = New System.Drawing. Point(24, 88)
Me.Button1.Name = "Button1"
Me.Button1.TabI ndex = 2
Me.Button1.Text = "Next"
'
'TextBox2
'
Me.TextBox2.Loc ation = New System.Drawing. Point(80, 56)
Me.TextBox2.Nam e = "TextBox2"
Me.TextBox2.Siz e = New System.Drawing. Size(112, 20)
Me.TextBox2.Tab Index = 3
Me.TextBox2.Tex t = "TextBox2"
'
'Button2
'
Me.Button2.Loca tion = New System.Drawing. Point(136, 88)
Me.Button2.Name = "Button2"
Me.Button2.TabI ndex = 4
Me.Button2.Text = "Add Child"
'
'Button3
'
Me.Button3.Loca tion = New System.Drawing. Point(240, 88)
Me.Button3.Name = "Button3"
Me.Button3.Size = New System.Drawing. Size(96, 23)
Me.Button3.TabI ndex = 5
Me.Button3.Text = "Delete Parent"
'
'Button4
'
Me.Button4.Loca tion = New System.Drawing. Point(376, 88)
Me.Button4.Name = "Button4"
Me.Button4.Size = New System.Drawing. Size(96, 23)
Me.Button4.TabI ndex = 6
Me.Button4.Text = "Show Changes"
'
'Button5
'
Me.Button5.Loca tion = New System.Drawing. Point(24, 16)
Me.Button5.Name = "Button5"
Me.Button5.TabI ndex = 7
Me.Button5.Text = "Load Data"
'
'CheckBox1
'
Me.CheckBox1.Ch ecked = True
Me.CheckBox1.Ch eckState = System.Windows. Forms.CheckStat e.Checked
Me.CheckBox1.Lo cation = New System.Drawing. Point(104, 16)
Me.CheckBox1.Na me = "CheckBox1"
Me.CheckBox1.Si ze = New System.Drawing. Size(64, 24)
Me.CheckBox1.Ta bIndex = 8
Me.CheckBox1.Te xt = "Async"
'
'Form1
'
Me.AutoScaleBas eSize = New System.Drawing. Size(5, 13)
Me.ClientSize = New System.Drawing. Size(496, 334)
Me.Controls.Add (Me.CheckBox1)
Me.Controls.Add (Me.Button5)
Me.Controls.Add (Me.Button4)
Me.Controls.Add (Me.Button3)
Me.Controls.Add (Me.Button2)
Me.Controls.Add (Me.TextBox2)
Me.Controls.Add (Me.Button1)
Me.Controls.Add (Me.TextBox1)
Me.Controls.Add (Me.DataGrid1)
Me.Name = "Form1"
Me.Text = "Form1"
CType(Me.DataGr id1, System.Componen tModel.ISupport Initialize).End Init()
Me.ResumeLayout (False)

End Sub

#End Region

Private Class DataAccess
Private Const SQL_CONNECTION_ STRING As String = _
"Data Source=localhos t;" & _
"Initial Catalog=Northwi nd;" & _
"Integrated Security=SSPI"

Public Event DataLoaded(ByVa l sender As Object, ByVal e As EventArgs)
Protected Overridable Sub OnDataLoaded(By Val e As EventArgs)
RaiseEvent DataLoaded(Me, e)
End Sub

Public Sub GetData(ByRef ds As DataSet)
ds = New DataSet
Dim da, da2 As SqlDataAdapter
Dim cnn As SqlConnection
Try
cnn = New SqlConnection(S QL_CONNECTION_S TRING)

da = New SqlDataAdapter( "SELECT * FROM Region", cnn)
da.Fill(ds, "Region")
da = New SqlDataAdapter( "SELECT * FROM Territories", cnn)
da.Fill(ds, "Territorie s")

ds.Relations.Ad d("Region_Terri tories", _
ds.Tables("Regi on").Columns("R egionID"), _
ds.Tables("Terr itories").Colum ns("RegionID") )

ds.DataSetName = "RegionTerritor ies"

OnDataLoaded(Ev entArgs.Empty)

Catch Exp As Exception
MessageBox.Show (Exp.Message)
End Try
End Sub

End Class

Private Delegate Sub GetDataArgsDele gate(ByVal e As EventArgs)

Private WithEvents Access As New DataAccess
Private myDataSet As DataSet
Private cmParent, cmChild As CurrencyManager

Private m_async As Boolean = True
Public Property LoadAsync() As Boolean
Get
Return m_async
End Get
Set(ByVal Value As Boolean)
m_async = Value
End Set
End Property

Private m_isDataLoaded As Boolean = False
Public Property IsDataLoaded() As Boolean
Get
Return m_isDataLoaded
End Get
Set(ByVal Value As Boolean)
m_isDataLoaded = Value
End Set
End Property

Private Sub Button5_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button5.Click
Me.Button5.Enab led = False
Me.BeginGetData ()
End Sub

Private Sub BeginGetData()
m_isDataLoaded = False
Me.DataGrid1.Da taSource = Nothing
Me.TextBox1.Dat aBindings.Clear ()
Me.TextBox2.Dat aBindings.Clear ()
Me.TextBox1.Tex t = ""
Me.TextBox2.Tex t = "Loading Data..."

If Me.LoadAsync Then
Dim t As New Threading.Threa d(AddressOf Me.GetData)
t.Name = Me.Name + "DataThread "
t.IsBackground = True
t.Start()
Else
Me.GetData()
End If
End Sub

Private Sub EndGetData(ByVa l e As EventArgs)
m_isDataLoaded = True

Me.DataGrid1.Da taSource = myDataSet
Me.DataGrid1.Da taMember = "Region.Region_ Territories"

Me.TextBox1.Dat aBindings.Add(" Text", myDataSet, "Region.RegionI D")
Me.TextBox2.Dat aBindings.Add(" Text", myDataSet,
"Region.RegionD escription")

cmParent = Me.BindingConte xt(myDataSet, "Region")
cmChild = Me.BindingConte xt(myDataSet, "Region.Region_ Territories")
Me.Button5.Enab led = True
End Sub

Public Sub GetData()
'Simulates a longer time.....
System.Threadin g.Thread.Sleep( 5000)
Access.GetData( myDataSet)
End Sub

Private Sub Access_DataLoad ed(ByVal sender As Object, ByVal e As
System.EventArg s) Handles Access.DataLoad ed
If Me.InvokeRequir ed Then
'-- Marshall to the UI thread...
Dim dlg As New GetDataArgsDele gate(AddressOf EndGetData)
Dim args() As Object = {e}
Me.BeginInvoke( dlg, args)
Else
Me.EndGetData(E ventArgs.Empty)
End If
End Sub

Private Sub Button1_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button1.Click
If Me.IsDataLoaded Then
cmParent.Positi on += 1
End If
End Sub

Private Sub Button2_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button2.Click
If Me.IsDataLoaded Then
cmChild.AddNew( )
End If
End Sub

Private Sub Button3_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button3.Click
If Me.IsDataLoaded Then
cmParent.Remove At(cmParent.Pos ition)
End If
End Sub

Public Overridable Sub ShowDiffData()
'-- View the diffgram in the web browser
Try
If Not (myDataSet Is Nothing) Then

Dim cFileName As String =
Environment.Get FolderPath(Envi ronment.Special Folder.LocalApp licationData) +
"\Diff"
Dim dsDiffgram As DataSet

If myDataSet.HasCh anges Then
dsDiffgram = myDataSet.GetCh anges()
dsDiffgram.Writ eXml(cFileName + myDataSet.DataS etName + ".xml",
XmlWriteMode.Di ffGram)
System.Diagnost ics.Process.Sta rt("file://" + cFileName +
myDataSet.DataS etName + ".xml")
Else
MessageBox.Show ("Please make changes first.", "Show Changes",
MessageBoxButto ns.OK, MessageBoxIcon. Information)
End If
End If
Catch exp As Exception
End Try
End Sub

Private Sub Button4_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button4.Click
If Me.IsDataLoaded Then
Me.ShowDiffData ()
End If
End Sub

Private Sub CheckBox1_Check edChanged(ByVal sender As System.Object, ByVal e
As System.EventArg s) Handles CheckBox1.Check edChanged
Me.LoadAsync = Me.CheckBox1.Ch ecked
End Sub
End Class

"Doug Bell" <du*@bigpond.co m> wrote in message
news:e9******** ******@TK2MSFTN GP12.phx.gbl...

Hi,
I have an application that has a "Data Access Class" and "User Interface
Class".

It is for receiving Purchase Order data from one system and pushing
processed transactions to another system.

The system generally works quite well.
Currently the User interface calls for a refresh of data every 15 minutes
(selectable) and the Data Access Class connects to the DB and retrieves
the
data structured to suit the application. During the retrieval it displays
messages informing the User of the various downloads. Each application has
its own Data Access Class. It takes between 30 seconds and 5 minutes to
refresh the data dependant on where the User is located

I have been asked to make the refresh transparent so that the User does
not
have to wait for the Data Access Layer to get its data as some site have a
very slow connections to the network.

I am not sure how to achieve this new requirement.
I thought that I could make the Data Access Class a separate application
that loads with the User interface and then periodically retrieves the
data
and saves it into a local database file (mdb ?) rather than into the
current
Data Set and then have the User Interface asynchronously connect to the
local database and update its records.

I would appreciate any oppinions.

Regards

Doug

[Cor Ligthert]

Doug,

I absolute don't see from your message what you are doing. I think that an
newsgroup message is not able to show that. You can try it however than it
becomes probably so long that nobody reads it, so it has no sense to explain
it more in my opinion.

However you asked an opinion. I surely would not go the direction in
duplicating your data in an access database. I have seen a lot of people
trying that in these newsgroups. It is difficult managable and cost as well
probably a lot of time.

To give you my first idea, that was creating XML files dataset on the server
and than distribute those on that 15 minute base by instance with a
webservice. (Where you than would have to decide if you create on your
server the xmlfiles on a time base or on demand).

However that last is just an idea that I got reading your message and never
did.

I hope this helps somehow

Cor

[Doug Bell]

Thanks Beth, I will have a look at that. I haven't done anything in
different threads before.
I wonder if I could get around locking access to the data by buffering it
into a secon data set, updating ds1 and then cloning ds1 to ds2 so that it
is only unavailable momentarily?

Thanjs

"Beth Massi [Architect MVP]" <bm****@comcast .net> wrote in message
news:eV******** ******@tk2msftn gp13.phx.gbl...

Hi Doug,

You can execute the loading of your data on a separate thread so that the
form is still responsive to the user, however, you need to be careful that
none of the UI elements work with that data before the data is retrieved.
Once the data is loaded, your data access class should raise an event that
you can handle so you can call the invoke method to marshal the call to the UI thread. Here's the basic idea (note- this example uses the SQL northwind database):

Public Class Form1
Inherits System.Windows. Forms.Form

#Region " Windows Form Designer generated code "

Public Sub New()
MyBase.New()

'This call is required by the Windows Form Designer.
InitializeCompo nent()

'Add any initialization after the InitializeCompo nent() call

End Sub

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Disp ose()
End If
End If
MyBase.Dispose( disposing)
End Sub

'Required by the Windows Form Designer
Private components As System.Componen tModel.IContain er

'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
Friend WithEvents DataGrid1 As System.Windows. Forms.DataGrid
Friend WithEvents TextBox1 As System.Windows. Forms.TextBox
Friend WithEvents Button1 As System.Windows. Forms.Button
Friend WithEvents TextBox2 As System.Windows. Forms.TextBox
Friend WithEvents Button2 As System.Windows. Forms.Button
Friend WithEvents Button3 As System.Windows. Forms.Button
Friend WithEvents Button4 As System.Windows. Forms.Button
Friend WithEvents Button5 As System.Windows. Forms.Button
Friend WithEvents CheckBox1 As System.Windows. Forms.CheckBox
<System.Diagnos tics.DebuggerSt epThrough()> Private Sub
InitializeCompo nent()
Me.DataGrid1 = New System.Windows. Forms.DataGrid
Me.TextBox1 = New System.Windows. Forms.TextBox
Me.Button1 = New System.Windows. Forms.Button
Me.TextBox2 = New System.Windows. Forms.TextBox
Me.Button2 = New System.Windows. Forms.Button
Me.Button3 = New System.Windows. Forms.Button
Me.Button4 = New System.Windows. Forms.Button
Me.Button5 = New System.Windows. Forms.Button
Me.CheckBox1 = New System.Windows. Forms.CheckBox
CType(Me.DataGr id1, System.Componen tModel.ISupport Initialize).Beg inInit() Me.SuspendLayou t()
'
'DataGrid1
'
Me.DataGrid1.An chor = CType((((System .Windows.Forms. AnchorStyles.To p Or
System.Windows. Forms.AnchorSty les.Bottom) _
Or System.Windows. Forms.AnchorSty les.Left) _
Or System.Windows. Forms.AnchorSty les.Right),
System.Windows. Forms.AnchorSty les)
Me.DataGrid1.Da taMember = ""
Me.DataGrid1.He aderForeColor = System.Drawing. SystemColors.Co ntrolText
Me.DataGrid1.Lo cation = New System.Drawing. Point(16, 120)
Me.DataGrid1.Na me = "DataGrid1"
Me.DataGrid1.Si ze = New System.Drawing. Size(472, 208)
Me.DataGrid1.Ta bIndex = 0
'
'TextBox1
'
Me.TextBox1.Loc ation = New System.Drawing. Point(24, 56)
Me.TextBox1.Nam e = "TextBox1"
Me.TextBox1.Siz e = New System.Drawing. Size(48, 20)
Me.TextBox1.Tab Index = 1
Me.TextBox1.Tex t = "TextBox1"
'
'Button1
'
Me.Button1.Loca tion = New System.Drawing. Point(24, 88)
Me.Button1.Name = "Button1"
Me.Button1.TabI ndex = 2
Me.Button1.Text = "Next"
'
'TextBox2
'
Me.TextBox2.Loc ation = New System.Drawing. Point(80, 56)
Me.TextBox2.Nam e = "TextBox2"
Me.TextBox2.Siz e = New System.Drawing. Size(112, 20)
Me.TextBox2.Tab Index = 3
Me.TextBox2.Tex t = "TextBox2"
'
'Button2
'
Me.Button2.Loca tion = New System.Drawing. Point(136, 88)
Me.Button2.Name = "Button2"
Me.Button2.TabI ndex = 4
Me.Button2.Text = "Add Child"
'
'Button3
'
Me.Button3.Loca tion = New System.Drawing. Point(240, 88)
Me.Button3.Name = "Button3"
Me.Button3.Size = New System.Drawing. Size(96, 23)
Me.Button3.TabI ndex = 5
Me.Button3.Text = "Delete Parent"
'
'Button4
'
Me.Button4.Loca tion = New System.Drawing. Point(376, 88)
Me.Button4.Name = "Button4"
Me.Button4.Size = New System.Drawing. Size(96, 23)
Me.Button4.TabI ndex = 6
Me.Button4.Text = "Show Changes"
'
'Button5
'
Me.Button5.Loca tion = New System.Drawing. Point(24, 16)
Me.Button5.Name = "Button5"
Me.Button5.TabI ndex = 7
Me.Button5.Text = "Load Data"
'
'CheckBox1
'
Me.CheckBox1.Ch ecked = True
Me.CheckBox1.Ch eckState = System.Windows. Forms.CheckStat e.Checked
Me.CheckBox1.Lo cation = New System.Drawing. Point(104, 16)
Me.CheckBox1.Na me = "CheckBox1"
Me.CheckBox1.Si ze = New System.Drawing. Size(64, 24)
Me.CheckBox1.Ta bIndex = 8
Me.CheckBox1.Te xt = "Async"
'
'Form1
'
Me.AutoScaleBas eSize = New System.Drawing. Size(5, 13)
Me.ClientSize = New System.Drawing. Size(496, 334)
Me.Controls.Add (Me.CheckBox1)
Me.Controls.Add (Me.Button5)
Me.Controls.Add (Me.Button4)
Me.Controls.Add (Me.Button3)
Me.Controls.Add (Me.Button2)
Me.Controls.Add (Me.TextBox2)
Me.Controls.Add (Me.Button1)
Me.Controls.Add (Me.TextBox1)
Me.Controls.Add (Me.DataGrid1)
Me.Name = "Form1"
Me.Text = "Form1"
CType(Me.DataGr id1, System.Componen tModel.ISupport Initialize).End Init()
Me.ResumeLayout (False)

End Sub

#End Region

Private Class DataAccess
Private Const SQL_CONNECTION_ STRING As String = _
"Data Source=localhos t;" & _
"Initial Catalog=Northwi nd;" & _
"Integrated Security=SSPI"

Public Event DataLoaded(ByVa l sender As Object, ByVal e As EventArgs)
Protected Overridable Sub OnDataLoaded(By Val e As EventArgs)
RaiseEvent DataLoaded(Me, e)
End Sub

Public Sub GetData(ByRef ds As DataSet)
ds = New DataSet
Dim da, da2 As SqlDataAdapter
Dim cnn As SqlConnection
Try
cnn = New SqlConnection(S QL_CONNECTION_S TRING)

da = New SqlDataAdapter( "SELECT * FROM Region", cnn)
da.Fill(ds, "Region")
da = New SqlDataAdapter( "SELECT * FROM Territories", cnn)
da.Fill(ds, "Territorie s")

ds.Relations.Ad d("Region_Terri tories", _
ds.Tables("Regi on").Columns("R egionID"), _
ds.Tables("Terr itories").Colum ns("RegionID") )

ds.DataSetName = "RegionTerritor ies"

OnDataLoaded(Ev entArgs.Empty)

Catch Exp As Exception
MessageBox.Show (Exp.Message)
End Try
End Sub

End Class

Private Delegate Sub GetDataArgsDele gate(ByVal e As EventArgs)

Private WithEvents Access As New DataAccess
Private myDataSet As DataSet
Private cmParent, cmChild As CurrencyManager

Private m_async As Boolean = True
Public Property LoadAsync() As Boolean
Get
Return m_async
End Get
Set(ByVal Value As Boolean)
m_async = Value
End Set
End Property

Private m_isDataLoaded As Boolean = False
Public Property IsDataLoaded() As Boolean
Get
Return m_isDataLoaded
End Get
Set(ByVal Value As Boolean)
m_isDataLoaded = Value
End Set
End Property

Private Sub Button5_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button5.Click
Me.Button5.Enab led = False
Me.BeginGetData ()
End Sub

Private Sub BeginGetData()
m_isDataLoaded = False
Me.DataGrid1.Da taSource = Nothing
Me.TextBox1.Dat aBindings.Clear ()
Me.TextBox2.Dat aBindings.Clear ()
Me.TextBox1.Tex t = ""
Me.TextBox2.Tex t = "Loading Data..."

If Me.LoadAsync Then
Dim t As New Threading.Threa d(AddressOf Me.GetData)
t.Name = Me.Name + "DataThread "
t.IsBackground = True
t.Start()
Else
Me.GetData()
End If
End Sub

Private Sub EndGetData(ByVa l e As EventArgs)
m_isDataLoaded = True

Me.DataGrid1.Da taSource = myDataSet
Me.DataGrid1.Da taMember = "Region.Region_ Territories"

Me.TextBox1.Dat aBindings.Add(" Text", myDataSet, "Region.RegionI D")
Me.TextBox2.Dat aBindings.Add(" Text", myDataSet,
"Region.RegionD escription")

cmParent = Me.BindingConte xt(myDataSet, "Region")
cmChild = Me.BindingConte xt(myDataSet, "Region.Region_ Territories")
Me.Button5.Enab led = True
End Sub

Public Sub GetData()
'Simulates a longer time.....
System.Threadin g.Thread.Sleep( 5000)
Access.GetData( myDataSet)
End Sub

Private Sub Access_DataLoad ed(ByVal sender As Object, ByVal e As
System.EventArg s) Handles Access.DataLoad ed
If Me.InvokeRequir ed Then
'-- Marshall to the UI thread...
Dim dlg As New GetDataArgsDele gate(AddressOf EndGetData)
Dim args() As Object = {e}
Me.BeginInvoke( dlg, args)
Else
Me.EndGetData(E ventArgs.Empty)
End If
End Sub

Private Sub Button1_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button1.Click
If Me.IsDataLoaded Then
cmParent.Positi on += 1
End If
End Sub

Private Sub Button2_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button2.Click
If Me.IsDataLoaded Then
cmChild.AddNew( )
End If
End Sub

Private Sub Button3_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button3.Click
If Me.IsDataLoaded Then
cmParent.Remove At(cmParent.Pos ition)
End If
End Sub

Public Overridable Sub ShowDiffData()
'-- View the diffgram in the web browser
Try
If Not (myDataSet Is Nothing) Then

Dim cFileName As String =
Environment.Get FolderPath(Envi ronment.Special Folder.LocalApp licationData) + "\Diff"
Dim dsDiffgram As DataSet

If myDataSet.HasCh anges Then
dsDiffgram = myDataSet.GetCh anges()
dsDiffgram.Writ eXml(cFileName + myDataSet.DataS etName + ".xml",
XmlWriteMode.Di ffGram)
System.Diagnost ics.Process.Sta rt("file://" + cFileName +
myDataSet.DataS etName + ".xml")
Else
MessageBox.Show ("Please make changes first.", "Show Changes",
MessageBoxButto ns.OK, MessageBoxIcon. Information)
End If
End If
Catch exp As Exception
End Try
End Sub

Private Sub Button4_Click(B yVal sender As System.Object, ByVal e As
System.EventArg s) Handles Button4.Click
If Me.IsDataLoaded Then
Me.ShowDiffData ()
End If
End Sub

Private Sub CheckBox1_Check edChanged(ByVal sender As System.Object, ByVal e As System.EventArg s) Handles CheckBox1.Check edChanged
Me.LoadAsync = Me.CheckBox1.Ch ecked
End Sub
End Class

"Doug Bell" <du*@bigpond.co m> wrote in message
news:e9******** ******@TK2MSFTN GP12.phx.gbl...

Hi,
I have an application that has a "Data Access Class" and "User Interface
Class".

It is for receiving Purchase Order data from one system and pushing
processed transactions to another system.

The system generally works quite well.
Currently the User interface calls for a refresh of data every 15 minutes (selectable) and the Data Access Class connects to the DB and retrieves
the
data structured to suit the application. During the retrieval it displays messages informing the User of the various downloads. Each application has its own Data Access Class. It takes between 30 seconds and 5 minutes to
refresh the data dependant on where the User is located

I have been asked to make the refresh transparent so that the User does
not
have to wait for the Data Access Layer to get its data as some site have a very slow connections to the network.

I am not sure how to achieve this new requirement.
I thought that I could make the Data Access Class a separate application
that loads with the User interface and then periodically retrieves the
data
and saves it into a local database file (mdb ?) rather than into the
current
Data Set and then have the User Interface asynchronously connect to the
local database and update its records.

I would appreciate any oppinions.

Regards

Doug

[Doug Bell]

Thanks Cor,
I understand it is difficult to see what I am trying to achieve.

I would rather keep it as a dataset in memory. And possibly I can do
something like using a different thread as Beth has suggested.

I did not mention but the data has to be available even when the AS400
Server is busy doing End Of Day and End Of Month stuff.
That is currently handled by writing the local Data Set to an XML when ever
it is refreshed but I think generating and distributing XML from the AS400
is out of the question.

Doug

"Cor Ligthert" <no************ @planet.nl> wrote in message
news:ut******** ******@TK2MSFTN GP14.phx.gbl...

Doug,

I absolute don't see from your message what you are doing. I think that an
newsgroup message is not able to show that. You can try it however than it
becomes probably so long that nobody reads it, so it has no sense to explain it more in my opinion.

However you asked an opinion. I surely would not go the direction in
duplicating your data in an access database. I have seen a lot of people
trying that in these newsgroups. It is difficult managable and cost as well probably a lot of time.

To give you my first idea, that was creating XML files dataset on the server and than distribute those on that 15 minute base by instance with a
webservice. (Where you than would have to decide if you create on your
server the xmlfiles on a time base or on demand).

However that last is just an idea that I got reading your message and never did.

I hope this helps somehow

Cor

[Cor Ligthert]

Doug,

Thanks Cor,
I understand it is difficult to see what I am trying to achieve.

I would rather keep it as a dataset in memory.
This does not change when you use the XML file as Intermidiate, only there
is not needed any action from the server, and probably will that save time.
(You can even think on zipping and dezipping it). (See my part about the
AS400 later).
And possibly I can do something like using a different thread as Beth has
suggested.
What do you than achieve with that. Or don't you have updates? That makes it
even more to try the solution I told.

I did not mention but the data has to be available even when the AS400
Server is busy doing End Of Day and End Of Month stuff.
That is currently handled by writing the local Data Set to an XML when
ever
it is refreshed but I think generating and distributing XML from the AS400
is out of the question.

Than I would probalby try directly to integrate an extra server in my
domain, that only gets that data, set it on a XMLfile dataset and is the
server for the clients to get that dataset.

However as I said I never tried.

Cor

[Cor Ligthert]

Dough,

I have looked better at the solution from Beth, there is nothing that
conflicts with my idea of a solution. You can integrate both.

Cor

[Cor Ligthert]

doh,

I have looked better at the solution from Beth, there is nothing that
conflicts with my idea of a solution. You can integrate both.
Assuming again that there are no updates needed. Cor

[Doug Bell]

Cor,
There are no updates.
Processed transactions go through a different system.

But I don't see how I can get AS400 to generate (and optionally zip) an XML
file?

I can see benefits if I could.

Doug

"Cor Ligthert" <no************ @planet.nl> wrote in message
news:ul******** ******@TK2MSFTN GP12.phx.gbl...

doh,

I have looked better at the solution from Beth, there is nothing that
conflicts with my idea of a solution. You can integrate both.

Assuming again that there are no updates needed.

Cor

[Cor Ligthert]

Doug,

But I don't see how I can get AS400 to generate (and optionally zip) an
XML
file?

Only with that extra server as I wrote.

That server collects the data from the AS400 in the same way as now the
clients do.

When ready write a zipped serialized dataset as a blob (bytearray).

With a Webservice you make it the client possible to get that blob.

The client do on seperated times (what can be even in a extra thread) the
collections of that blob using that webservice, unzip it and read (or
deserialize it) it in the proper place when it is arrived.

However again just an idea with what I see directly not much problems to
realise when you have somewhere a server which you can use for that. (It
needs IIS and ASPNET).

Cor