Visual Basic

Re: VC++ "Handle" type causing issues in .NET

14-Apr-06 12:06

Try passing the parameter ByVal instead of ByRef. For handles, the correct datatype should be IntPtr:

Public Declare Function DeviceOpen Lib "PLXAPI.DLL" _
    Alias "PlxPciDeviceOpen" ( _
    ByRef Device As PCIDevice, _
    ByVal PCIDevHandle As IntPtr) As Integer

If not done correctly, you might also have a problem with the PCIDevice type, whatever that is.

Dave Kreskowiak
Microsoft MVP - Visual Basic

REnginear15-Apr-06 12:59

REnginear

15-Apr-06 12:59

Thank you very much. Even with Byval, the System.nullexcepton occurs and infact I do not get a handle value at all. (With ByRef, I do get the correct handle back as an integer along with the system.nullexception.

--this is how the handle type is defined in the PLXAPI.DLL
typedef void *HANDLE; (in winnt.h)

typedef HANDLE PLX_DRIVER_HANDLE;
typedef int PLX_DRIVER_HANDLE;
--

So, I think that Handle is an integer in VB.NET?? However the structure type, as you suggested, has a problem:

The structure is defined as:

(in DLL)

typedef struct _DEVICE_LOCATION
{
U8 BusNumber;
U8 SlotNumber;
U16 DeviceId;
U16 VendorId;
U8 SerialNumber[12];
} DEVICE_LOCATION;

----------------
VB.NET Structure - my equivalent

Structure PCIDevice
Dim BusNumber As Byte
Dim SlotNumber As Byte
Dim DeviceId As Short
Dim VendorId As Short
Dim SerialNumber() As Byte
End Structure
---------

Values sent to DLL (which modifies these values and I think thats where it is crashing!!!!)

dim device as pcidevice
Dim serialno As String = "PCI9030-0"
Device.BusNumber = System.Convert.ToByte(1)
Device.SlotNumber = System.Convert.ToByte(0)
Device.VendorId = System.Convert.ToUInt16(&H10B5)
Device.DeviceId = System.Convert.ToUInt16(&H9030)
ReDim Device.SerialNumber(11)

Device.SerialNumber = serialno.ToCharArray

---------
DLL DEBUG LOG SAYS:

Dev->BusNumber = 01
Dev->SlotNumber = 00
Dev->DeviceId = 9030
Dev->VendorId = 10B5
Dev->SerialNumber =
-------
serial number field goes in blank. so it is nto translated correctly. All the rest of the values are correct. On return, the DLL tries to write to the serial number "PCI-9030-0" back to the structure in the serial number field and I that is where I think it is failing. the serial number is assinged by teh dll in this generic fashion and since there i sonly one PCI-9030 device in our setup, that number never changes.

So, somehow I have to translate the serialNumber field to teh DLL correctly and make it a datatype that the C dll can write to.

Re: VC++ "Handle" type causing issues in .NET

REnginear16-Apr-06 13:58

REnginear

16-Apr-06 13:58

Thanks all,

the serial number field needed to be 'Long'. and handle works as intptr, integer either.

this problem has been resolved!

Dataset bound to combobox

G7236014-Apr-06 9:28

G72360

14-Apr-06 9:28

Hey,

I'm having a little problem.
In my applicaton I have a combobox that is bound to a dataset. The dataset retrieves "Users" from my database. My combobox is bound as follows:

cboIncidentHandler.DataSource = busAllUsersDS.Tables("tbl_IMS_Users")<br />
        cboIncidentHandler.DisplayMember = "UserFullName"<br />
        cboIncidentHandler.ValueMember = "UserId"

Now, I have some textfields I want to be filled up with other data from the dataset (like UserEmail, UserPhone, etc.).

Is there someone who can help me out with this? What is the best way to do this? Confused | :confused:

Thanks in advance!!!

G72360

Re: Dataset bound to combobox

Dave Kreskowiak17-Apr-06 4:24

Advice for tracking a recordset change - Hash Value?

17-Apr-06 4:24

Depending on the functionality you want, this is easy enough.

On the SelectedIndexChanged (? from memory) event, get the ValueMember and do another lookup on the database that returns the fields you want based on that UserId number. You can either directly change the Text properties of your TextBox's from the record that is returned or bind the TextBox's Text properties to each field.

Dave Kreskowiak
Microsoft MVP - Visual Basic

Brad6ft414-Apr-06 7:59

Re: Advice for tracking a recordset change - Hash Value?

14-Apr-06 7:59

I am working within a VB.NET [windows forms application] /SQL Server 2000 db. When a user changes the recordset I want to be able to notify the others that reload this recordset that this record has been modified.

A colleague of mine recommended that I add a Hash value to the changed recordset. This way I can compare the hash values to see if the recordset has been modified.

Having never worked with the Hash Algorithm but after reading about it, sounds like the right plan to follow.

However, I cannot find a tutorial on working with hash values with a recordset and wondered if someone had some advice on this subject.

Any help would be greatly appreciated,

Thanks in advice & Happy Easter,

~Brad Confused | :confused:

-- modified at 14:15 Friday 14th April, 2006

Dave Kreskowiak14-Apr-06 8:26

Re: Advice for tracking a recordset change - Hash Value?

14-Apr-06 8:26

There's a problem with this. Your clients would have to have a central server to accept change notifications and relay them to the other clients.

You might want to look at SQL Server's Notification Services[^] first.

Dave Kreskowiak
Microsoft MVP - Visual Basic

Brad6ft414-Apr-06 8:47

Re: Advice for tracking a recordset change - Hash Value?

14-Apr-06 8:47

Dave,

Currently this Application is running on a server. It has 10 or more client machines that all use the same log in to the Application using the same Username found within Active Directory / roles.

Scenerio:

Inside my App. I have a datagrid that I populate using an SQL StoredProc to display records to the user. The problem is because the Application has only 1 log in, I cannot verify which user has changed the recordset. When 1 or more users opens a record to modify it, I allow the first user to have control over the record and display a message to the other users that try to open it. I perform this by setting a different value to the tables record being modified. The problem arise when the user that has modified the recordset and saves the record to the Db. The other users are now seeing the old recordsets in their datagrid because I have no way to automatically REFRESH their screens with the new datagrid recordset information.

A colleague of mine suggested that I add a Hash value to the record uponLOAD of the datagrid then when the user changes the state of the record I can see if the value has been changed. If I know it has been changed then I can notify the users to REFRESH their screens for their datagrid.

I do not have an Audit trail table that I can access to see if a particular user is working on a particualr table. In addition, I think that b/c I am using Active directory with only 1 Log In Username, I really cannot follow what each Client machine is doing to the records in my DB.

Any advice would be greatly appreciated as I am stumped as to how I can fix this issue within my Application.

Thanks in advance,

~Brad Confused | :confused:

Dave Kreskowiak14-Apr-06 9:28

Re: Advice for tracking a recordset change - Hash Value?

14-Apr-06 9:28

None of this has any bearing on the problem if you use Notification Services. Clients register for notifications of changes to the underlying database. If a record is changed and there are clients registered for notifications, then each client will get a change event they can handle to refresh their datasets.

You really don't need a hash table for anything. The only other way to do this is to write a server component that manages access to the database for the clients. The clients communicate with the server component and "check out" blocks of records in the database. Frankly, you'd be writing an alternative to Notification Services.

Dave Kreskowiak
Microsoft MVP - Visual Basic

Brad6ft417-Apr-06 4:42

Re: Advice for tracking a recordset change - Hash Value?

17-Apr-06 4:42

Dave,

SQL Notification is something very cool and something I will definitlly look into it in order to increase my arsenal of design techniques. However for this particular functionanlity it is quite innapropriate (over kill to say the least). From what i read/understand, the notification makes sense when you have data driven behavior, this is not the case with the functionality of my Application.

For my App. I simply want to check if a row has changed or not. Not act when a row has changed. I am not sure if you see the nuance.

All this to say, SQL Notification is nice, however, not for my application. With the research I now know from your help/advice I may apply it when it fits the model or a behaviour that lends itself to it, keyword is "data driven behaviour" and this is not my Application, though I thank you for your advice.

I found an approach that I will implement for my particular situation, called the hash signature <a href="http://en.wikipedia.org/wiki/Hash_function" rel="nofollow">http://en.wikipedia.org/wiki/Hash_function</a>[<a href="http://en.wikipedia.org/wiki/Hash_function" target="_blank" rel="nofollow" title="New Window">^</a>]

Thanks again,

~Brad
Smile | :)

Dave Kreskowiak17-Apr-06 12:29

Re: Advice for tracking a recordset change - Hash Value?

17-Apr-06 12:29

Brad6ft4 wrote:
quite innapropriate (over kill to say the least).

Yeah? Wait till you get done implementing this in your own code. You'll sit back, look at this code, and think, "Hey, maybe it wasn't overkill after all..."

Brad6ft4 wrote:
I simply want to check if a row has changed or not.

Precisely when do you want to do this? Theres a couple of ways of doing this, but what works depends on your requirements. You have a concurrency problem.

You can lock the records so that only one client gets a Read/Write copy of the data, but if all your clients on working on the same set of records, this won't work. The first client to lock the records is the ONLY client that gets to ever attempt to write any changes back.

If that doesn't work for you, you'll have to implement some kind of "checkout" scheme in your SQL. Since each client has to check to see if the record they have is different from the one it has already, you have to read the values from the database BEFORE you can write the changed data back. The record can change between the time any one client reads it to check for a change and when that same client attempts to write the change back out to the database. You'll have to implement some kind of locking mechanism so that when you read a record to check for a change, you're actually "checking it out" like a book from the library. This part MUST be done in a stored procedure in the database.

From a logic point of view, the stored proc has to attempt to check the record out before it checks to see if the record changed, THEN read and pass it to the client. You'll have to implement a "check out" scheme in SQL. pass some kind of ReadOnly flag in the dataset to go with it. The database has to tell any client that attempts to check to see if it can write data back to the database that the record is already checked out.

Now, using Notification Services, if a record changes, it can automatically notify each client to do something very simple. Re-query the database for this one record.

It's your call...

Dave Kreskowiak
Microsoft MVP - Visual Basic

Brad6ft422-Apr-06 6:33

objectdatasource has no values to insert

22-Apr-06 6:33

Dave,

I found an easier solution [Quick & Dirty] but works well to resolve my issue. Instead of using the Hash function and /or your Smile | :)

suggestion of using SQL Server Notification which for this particular case would have been over kill.

I simply used a check on the tables field name DateModified datetime.

Once the user selects a particular record, upon retrieval of that record, I set a field within my table, to the status of EDIT_MODE [EDIT_MODE = 1]. After which I take the datetime inside the recordset and use it as a marker for later use. If that record is changed, upon the Save() of that record, I set the DateModified date = datetime.Now().

With this approach, I can notify the user making he/she aware that the record they are trying to view has been changed by another user and that they should REFRESH their initial Search criteria to obtain the new recordset of that particular record.

Thanks for all your help,

~Brad
Wink | ;)

dr S.A.f.14-Apr-06 2:43

dr S.A.f.

14-Apr-06 2:43

Hi,
I used the example from http://blog.binaryocean.com/PermaLink,guid,a1ff6cab-dc2d-441c-8557-7dce920d4075.aspx
to create an insertable gridview, My code is identical, apart from the language being C# in the example and VB.NET in my project.

Everything works, except the inserting, when I insert data and press the save button I get an InvalidOperationException in the method

Protected Sub gvAgendaPunten_RowCommand(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewCommandEventArgs) ' Handles gvAgendaPunten.RowCommand
        If e.CommandName = "Save" Then
            Dim agendaPunt As String = CType(gvAgendaPunten.FooterRow.FindControl("txtAgendaPunt"), TextBox).Text
            Dim vergaderingId As Integer = ddlVergaderingen.SelectedValue
            odsAgendaPunten.InsertParameters.Add("agendaPunt", agendaPunt)
            odsAgendaPunten.InsertParameters.Add("vergaderingId", vergaderingId)
            odsAgendaPunten.Insert()
           
        End If
    End Sub

saying that the ObjectDataSource 'odsAgendaPunten' has no values to insert. Check that the 'values' dictionary contains values.
But the funny thing is dat my odsAgendaPunten.insertparameters has count 2 and items 0 and 1 have the values from agendaPunt and vergaderingId.

I also tried with setting the parameters before, in the source code and via the objectdatasource properties window, nothing seems to work.

If anyone could help me out here, or tell me in what direction to look. I'd appreciate it very much.

I don't think it's necessary to post the rest of the code, since the error must be located in this method (I think), but If it would clear things up, just let me know, and I'll post the rest of it too.

thx
davy.

Re: objectdatasource has no values to insert

Steve Pullan14-Apr-06 3:50

Steve Pullan

14-Apr-06 3:50

I have not used this before, but looking at the code, the author of the sample has separated out the Inserting() event and it is here that the calls to InsertParameters are made.

I think you'll find that the call to Insert() in the RowCommand event raises the Inserting() event on the object which you have not provided hence the error.

...Steve

1. quod erat demonstrandum
2. "Give a man a fish and you've fed him for a day. Teach him how to fish and you've fed him for life." I read that somewhere once Smile | :)

Re: objectdatasource has no values to insert

dr S.A.f.14-Apr-06 8:20

dr S.A.f.

14-Apr-06 8:20

Imports System.data
Partial Class VergaderingWijzigen
    Inherits System.Web.UI.Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not Page.IsPostBack() Then
            fillDropDownList()
            Dim key() As String = {"agendaPuntId"}
            gvAgendaPunten.DataKeyNames = key
            gvAgendaPunten.Visible = False
        Else
            gvLeden.DataBind()
        End If
    End Sub
    Private Property loadDataEmpty()
        Get
            Return CType(ViewState("loadDataEmpty"), Boolean)
        End Get
        Set(ByVal value)
            ViewState("loadDataEmpty") = value
        End Set
    End Property
    Protected Sub fillDropDownList()
        Dim collectionVergaderingen As IDataReader = DatabaseAgent.selectUsersVergaderingen("ST")
        ddlVergaderingen.DataSource = collectionVergaderingen
        ddlVergaderingen.DataTextField = "titel"
        ddlVergaderingen.DataValueField = "vergaderingid"
        ddlVergaderingen.DataBind()
        collectionVergaderingen.Close()
        If ddlVergaderingen.Items.Count = 0 Then
            ddlVergaderingen.Visible = False
            lblError.Visible = True
            lblError.Text = "Er zijn geen vergaderingen gepland die u kunt wijzigen"
        Else
            lblError.Visible = True
            ddlVergaderingen.Visible = True
            ddlVergaderingen.Items.Add(New ListItem("Selecteer vergadering", -1))
            ddlVergaderingen.SelectedValue = -1
        End If


    End Sub

    Protected Sub DropDownList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlVergaderingen.SelectedIndexChanged
        gvAgendaPunten.Visible = True
    End Sub

    Protected Sub odsAgendaPunten_Inserting(ByVal sender As Object, ByVal e As ObjectDataSourceMethodEventArgs) Handles odsAgendaPunten.Inserting
        e.InputParameters("agendaPunt") = CType(gvAgendaPunten.FooterRow.FindControl("txtAgendaPunt"), TextBox).Text
        e.InputParameters("vergaderingId") = ddlVergaderingen.SelectedValue
    End Sub

    Protected Sub odsAgendaPunten_Selected(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.ObjectDataSourceStatusEventArgs) Handles odsAgendaPunten.Selected
        If Not e.Exception Is Nothing Then
            Throw e.Exception
        End If
        Dim d As DataTable = CType(e.ReturnValue, DataSet).Tables.Item(0)
        If d.Rows.Count = 0 Then
            d.Rows.Add(d.NewRow())
            loadDataEmpty = True
        Else
            loadDataEmpty = False
        End If
    End Sub

    Protected Sub odsAgendaPunten_Selecting(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.ObjectDataSourceSelectingEventArgs) Handles odsAgendaPunten.Selecting
        Console.Write("hallo")
    End Sub

    Protected Sub gvAgendaPunten_RowCommand(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewCommandEventArgs) Handles gvAgendaPunten.RowCommand
        If e.CommandName = "Save" Then
            odsAgendaPunten.Insert()
        End If
    End Sub

    Protected Sub gvAgendaPunten_RowCreated(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles gvAgendaPunten.RowCreated
        If (loadDataEmpty) And e.Row.RowType = DataControlRowType.DataRow Then
            e.Row.Visible = False
            e.Row.Controls.Clear()
        End If
    End Sub

    Protected Sub gvAgendaPunten_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles gvAgendaPunten.SelectedIndexChanged

    End Sub
  
    Protected Sub btnAddAgendaPunt_Click1(ByVal sender As Object, ByVal e As System.EventArgs)
        DatabaseAgent.insertAgendaPunt(New DAgendaPunt(ddlVergaderingen.SelectedValue, CType(gvAgendaPunten.FindControl("txtAgendaPunt"), TextBox).Text))
    End Sub
End Class

This is the complete codebehind. (the way it looked before I started to try out several things to get it to work.)
I do have code for the inserting event, offcourse I forgot to mention that in my first post Smile | :)

Or do I have to raise that event somewhere manually?

Vb 6 and access 2000 in LAN

arunendra14-Apr-06 2:11

14-Apr-06 2:11

Hi!
I have developed an application using visual basic 6. I have used access 2000 database and crystal report( for reporting). Now, i want the database to stay in one machine of the workgroup so that other machines can connect (can insert/update and view reports), simply i want it to be a client server application. My questions are :
1.How to configure the machine ( where the database will stay) so that others can use the databse?
2.I have used file dsn for crystal report as i want other machines to use the reports, so is it necesary for the reports to stay with each client application and also how do i find the file dsn of the machine where the database stays?
3.what will be the ado conect string for the clients to connect to the database in the lan?
Regads
Arunendra

Dave Kreskowiak14-Apr-06 3:34

14-Apr-06 3:34

arunendra wrote:
1.How to configure the machine

Access is NOT a good shareable database. It was meant to be a Desktop database. It'll work, but you have to maintain (compact and repair) that database religously! Also, maintenance on the database will take it offline until the maintenance is complete. This means that your application cannot run until your done!

This depends on your machine environment. I highly recommend reading up on Windows networking and security first. But, the basic thing is to setup a Share on the server and put your database files on that share. Then, each workstation has to map a drive to that Share. Excatly how this is done depends on if your machines are in a workgroup or domain. How you setup the Share and NTFS security also depends on this configuration.

arunendra wrote:
2.I have used file dsn for crystal report

I don't use Crystal Reports, so I couldn't tell you...

arunendra wrote:
3.what will be the ado conect string for the clients to connect to the database in the lan?

The same as what your using now. Only you'll have to specify the network drive letter you mapped setting up Windows networking, and specify the full path to the .MDB file.

Dave Kreskowiak
Microsoft MVP - Visual Basic

arunendra14-Apr-06 5:15

14-Apr-06 5:15

Thanks Dave for your reply.
I know Access is not for sharing but the requirement is such that i have to use access. I have a code , therefore, in my application which will automatically run the compact database service everyday at a specific time.
I actually need the code to perform what I need. for eg, if the folder in which the database resides is called "x', and the name of the mdb file is "data.mdb", then, how do I make sure that users can open from other locations,
i have set read & execute,list folder contents,read, write permission for everyone and also have set the same permission for the mdb file. have i done something wrong?

also i have tried the following code for connecting from the client :

Connect_String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=\\machine_name\x\data.mdb;Persist Security Info=False;Jet OLEDB:Database Password=bill1234"
con.open connect_string

but when run from another machine i get the following error msg :
( not exact!!) "the \\machine_name\x\data.mdb can not be opened as this may be not permitted or exclusively locked"

Regarding the crystal report problem, i think i need to know only one thing, i.e. how to share the file dsn that i have used for the crystal report. to be specific, how should i configure the file dsn that i already have in the machine where i have the database, i think that will make the reports available in the client machines. so, can you help me for sharing the file dsn in proper manner.

Regadrs
Arunendra

N.B. I will soon want to learn how to connect to a sql server database in a workgroup and also in a domain, i think you can help me out in that also, but currently please get me out of this.

-- modified at 11:16 Friday 14th April, 2006

Dave Kreskowiak14-Apr-06 6:43

14-Apr-06 6:43

arunendra wrote:
if the folder in which the database resides is called "x', and the name of the mdb file is "data.mdb", then, how do I make sure that users can open from other locations,

Have you setup a share on folder X?? A UNC path takes the format \\machineName\shareName\folder\filename. In your case, if you create a Share on folder X and called that share "Data", then the UNC path would be \\machine_name\Data\mydata.mdb.

As for the FileDSN, the default location for the file is C:\Program Files\Common Files\ODBC\Data Sources. I would suggest copying the FileDSN to that folder on each client machine.

Dave Kreskowiak
Microsoft MVP - Visual Basic

arunendra14-Apr-06 7:10

14-Apr-06 7:10

Thanks again for such a quick reply.
First of all what is UNC? I have given permission a set of permission to that folder (x) and the mbd (data) which i have given in the earlier letter.
Mostly i have given all the permissions except for the full control. do u think it will be sufficient?

second, regarding file dsn, will this problem solve, if i just copy the actual dsn (say mydsn.dsn) file and paste them in each location ( the location you have given)? Or may I try using the odbc manager in each pc and just add the dsn from the remote pc? what should i do?

Regards
arunendra

Dave Kreskowiak14-Apr-06 7:14

14-Apr-06 7:14

arunendra wrote:
First of all what is UNC?

UNC stands for Universal Naming Convention. If you sis not create a SHARE, which you have never mentioned you did, then the security setup won't make a difference. You MUST MUMST MUST MUST create a SHARE on the X folder. Right click the X folder, click on "Sharing...", then click on "Share this folder". Give the share a name...

Yes, you can copy the FileDSN file over to the client workstations and it'll work.

Dave Kreskowiak
Microsoft MVP - Visual Basic

arunendra14-Apr-06 23:35