Visual Basic Q&A

Symptoms
The Pinnacle-BPS Graph control shipping with Visual Basic gives usersthe ability to create pie charts. The Pinnacle-BPS is a relatively largecontrol and uses a large amount of disk space on distribution disks.Therefore, the custom effects available are limited to the features of thecontrol. The Circle method in the VBA language provides functionality todraw arcs and segments. By drawing segments, you can easily create a piechart and add custom features as you require. Below is a code sampledemonstrating how to do this.
Resolution
Start a new Visual Basic project. Form1 is created by default.Place a Command button on the form.Place a 200×200 pixel Picture box on the form.Add the following code to the Form1 code window:

Option ExplicitPublic Sub DrawPiePiece(lColor As Long, fStart As Double, fEnd AsDouble)Const PI As Double = 3.14159265359Const CircleEnd As Double = -2 * PIDim dStart As DoubleDim dEnd As DoublePicture1.FillColor = lColorPicture1.FillStyle = 0dStart = fStart * (CircleEnd / 100)dEnd = fEnd * (CircleEnd / 100)Picture1.Circle (100, 100), 60, , dStart, dEndEnd SubPrivate Sub Command1_Click()Picture1.ScaleMode = vbPixelsCall DrawPiePiece(QBColor(1), 0.001, 36)Call DrawPiePiece(QBColor(2), 36, 55)Call DrawPiePiece(QBColor(3), 55, 75)Call DrawPiePiece(QBColor(4), 75, 99.999)End Sub Press the F5 key to run the project. You should see a pie chart beingdrawn with four sections mirroring the four times that the DrawPieceroutine was called in the Command1_Click event.

Symptoms
The Stream object introduced in ActiveX Data Objects (ADO) 2.5 can be used to greatly simplify the code that needs to be written to access and modify Binary Large Object (BLOB) data in a SQL Server Database. The previous versions of ADO [ 2.0, 2.1, and 2.1 SP2 ] required careful usage of the GetChunk and AppendChunk methods of the Field Object to read and write BLOB data in fixed-size chunks from and to a BLOB column. An alternative to this method now exists with the advent of ADO 2.5. This article includes code samples that demonstrate how the Stream object can be used to program the following common tasks: Save the data stored in a SQL Server Image column to a file on the hard disk.Move the contents of a .gif file to an Image column in a SQL Server table.
Resolution
The following code samples are based on the data stored in the pub_info table in the SQL Server 7.0 pubs sample database. You need to modify the ADO connection string to point to your SQL Server installation. Example 1 : Saving the Data in a SQL Server Image Column to a File on the Hard Disk The code in this example opens a recordset on the pub_info table in the pubs database and saves the binary image data stored in the logo column of the first record to a file on the hard disk, as follows: Open a new Standard EXE Visual Basic project.On the Project menu, click to select References, and then set a reference to the Microsoft ActiveX Data Objects 2.5 Object Library.Place a CommandButton control on Form1.Make the following declarations in the form’s General declarations section:

Dim cn As ADODB.ConnectionDim rs As ADODB.RecordsetDim mstream As ADODB.Stream Cut and paste the following code into the Click event of the CommandButton that you added to the form:

Set cn = New ADODB.Connectioncn.Open “Provider=SQLOLEDB;data Source=<name of your SQL Server>;Initial Catalog=pubs;User Id=<Your Userid>;Password=<Your Password>”Set rs = New ADODB.Recordsetrs.Open “Select * from pub_info”, cn, adOpenKeyset, adLockOptimisticSet mstream = New ADODB.Streammstream.Type = adTypeBinarymstream.Openmstream.Write rs.Fields(“logo”).Valuemstream.SaveToFile “c:\publogo.gif”, adSaveCreateOverWriters.Closecn.Close Save and run the Visual Basic project.Click the CommandButton to save the binary data in the logo column of the first record to the file c:\publogo.gid. Look for this file in Windows Explorer and open it to view the saved image.
The code in this example declares an ADODB Stream object and sets its Type property to adTypeBinary to reflect that this object will be used to work with Binary data. Following this, the binary data stored in the logo column of the first record in the pub_info table is written out to the Stream object by calling its Write method. The Stream object now contains the binary data that is saved to the file by calling its SaveToFile method and passing in the path to the file. The adSaveCreateOverWrite constant passed in as the second parameter causes the SaveToFile method to overwrite the specified file if it already exists.Example 2 : Transfer the Image Stored in a .gif File to an Image Column in a SQL Server Table The code in this example saves an image stored in a .gif file to the logo column in the first record of the pub_info table by overwriting its current contents, as follows: Open a new Standard EXE Visual Basic project.On the Project menu, click to select References, and then set a reference to the Microsoft ActiveX Data Objects 2.5 Object Library.Place a CommandButton on Form1. Make the following declarations in the form’s General declarations section:

Dim cn As ADODB.ConnectionDim rs As ADODB.RecordsetDim mstream As ADODB.Stream Cut and paste the following code in the Click event of the CommandButton that you added to the form:

Set cn = New ADODB.Connectioncn.Open “Provider=SQLOLEDB;data Source=<name of your SQL Server>;Initial Catalog=pubs;User Id=<Your Userid>;Password=<Your Password>”Set rs = New ADODB.Recordsetrs.Open “Select * from pub_info”, cn, adOpenKeyset, adLockOptimisticSet mstream = New ADODB.Streammstream.Type = adTypeBinarymstream.Openmstream.LoadFromFile “<path to .gif file>”rs.Fields(“logo”).Value = mstream.Readrs.Updaters.Closecn.Close Save and run the Visual Basic project.Click on the CommandButton to run the code to stream the contents of the .gif file to the ADO Stream object, and save the data in the Stream to the logo column in the first record of the recordset.Verify that the image in the logo column has been modified by using the code in Example 1.

Symptoms
If you run commands or call methods of the SqlCommand or OleDbCommand object, you receive the following error message if a connection is not open:

An unhandled exception of type ‘System.InvalidOperationException’ occurred in system.data.dll
Additional information: ExecuteReader requires an open and available Connection (state=Closed).
Resolution
The DataAdapter object does not require that you explicitly open a connection to run some of its methods. Therefore, you can call the Update or Fill method of the DataAdapter object when the connection is closed. The Connection object that is associated with the SELECT statement must be valid, but it does not need to be open. If you close the connection before you call Fill, the connection is opened to retrieve the data and then closed. If the connection is open before you call Fill, it remains open.
Steps to Reproduce the BehaviorStart Microsoft Visual Studio .NET.Create a new Windows Application project in Visual Basic .NET. Form1 is added to the project by default.Make sure that your project contains a reference to the System.Data namespace, and add a reference to this namespace if it does not.Place two Button controls and one DataGrid control on Form1. Button1, Button2, and DataGrid1 are created by default.Change the Name property of Button1 to btnDataAdapter and the Text property to DataAdapter.
Change the Name property of Button2 to btnCommand and the Text property to Command.Use the Imports statement on the System and System.Data namespaces so that you are not required to qualify declarations in those namespaces later in your code. Add the following code to the “General Declarations” section of Form1:

Imports SystemImports System.Data.OleDbImports System.Data.SqlClient In the Code window, copy and paste the following code after the “Windows Form Designer generated code” region:

Private Sub btnDataAdapter(ByVal sender As System.Object, _ByVal e As System.EventArgs) Handles btnDataAdapter.ClickDim myConnString As String = _”User ID=sa;password=sa;Initial Catalog=Northwind;Data Source=myServer”Dim mySelectQuery As String = _”Select * From Customers Where CustomerID Like ‘A%’”Dim con As New SqlConnection(myConnString)’The code works fine even if you comment out the next line (to open the connection).con.Open()Dim daCust As New SqlDataAdapter(mySelectQuery, con)Dim ds As New DataSet()daCust.Fill(ds, “Cust”)DataGrid1.DataSource = dsDataGrid1.DataMember = “Cust”End SubPrivate Sub btnCommand(ByVal sender As System.Object, _ByVal e As System.EventArgs) Handles btnCommand.ClickDim myConnString As String = _”User ID=sa;password=sa;Initial Catalog=Northwind;Data Source=myServer”Dim mySelectQuery As String = _”Select * From Customers Where CustomerID Like ‘A%’”Dim con As New SqlConnection(myConnString)Dim myCommand As New SqlCommand(mySelectQuery, con)’An exception is thrown if you comment out the next line (to open the connection).con.Open()Dim myReader As SqlDataReader = myCommand.ExecuteReader()While myReader.Read()’Process data.End WhilemyReader.Close()con.Close()End Sub Modify the connection string (myConnString) as appropriate for your environment.Save your project. On the Debug menu, click Start to run your project.Comment out the line of code that opens the connection. Notice that DataAdapter.Fill works as expected, but Command.ExecuteReader fails with the above-mentioned exception.

Symptoms
A project compiled in native code shows poor performance. This behavioroccurs because the project contains calls to subroutines using the GoSubstatement.
Resolution
The GoSub statement has not been optimized in Visual Basic.

Symptoms
An MDIFORM does not show the child form in the WindowList menu if the childform is a Data Report. If the Data Report is minimized and then returned toa normal state, it will show up in the WindowList.
Resolution
To work around this problem, add code to your program that minimizes thereport prior to opening the report in normal mode. Refer to the Steps toReproduce Behavior section of this article for sample code on thisworkaround.

Symptoms
When you are debugging a Microsoft Visual Studio 2005 application and you try to set the next statement, you may receive an error message that resembles the following error message:

Unable to set the next statement to this location. There is no executable code at this location in the source code.
Resolution
The Debugger Engine is picking the statements in sequence. As long as the caret is at the end of the line, the Debugger Engine will set the next statement on the next line. If there is no executable code from the next line, an error message will occur.