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Implementing a Factory Pattern in ASP.NET

factory pattern diagram

A question posed by @Ramsharma1234 on Twitter this morning asked how to implement Factory Patterns in ASP.NET.

(definition of Factory Pattern)

Below is what would be considered a very basic form of Factory Pattern.  This method will essentially instantiate a generic Object, which is the parent of all types of Objects, and later be treated as if it were the type of child object that is used as a parameter in calling the method.  On a Web site where I needed to build Web controls dynamically, based on values from a database query, I created a method called “AddControl” that would add a generic Object to a Placeholder on my Web form:

Private Sub AddControl(ByVal oControl As Object)
   Placeholder1.Controls.Add(oControl)
End Sub

To call this method, I would instantiate a Web control such as a Button and add it to the Placeholder with the method:

Dim btnPrint As New Button
btnPrint.Attributes.Add("onclick", "javascript:window.print();")
btnPrint.Visible = False
AddControl(btnPrint)

Any type of Web control (TextBox, Label, Literal, etc.) could be instantiated and then added using this method.  For instance, if the table value for a particular field indicated the creation of a TextBox, this would be how that could be accomplished:

Dim oControl As New Object
'...
oControl = New TextBox
With oControl
.ID = strFieldName & "_mltxt"
.TextMode = TextBoxMode.MultiLine
.MaxLength = 2000
.Style("overflow") = "hidden"
.Height = 300
.Width = 500
.BorderStyle = BorderStyle.None
.Enabled = True
.ReadOnly = True
End With
AddControl(oControl)
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Setting the Connection String Programmatically on a Crystal Reports ReportDocument

logos for Visual Studio and Crystal Reports

Programmatically setting the connection string for a Crystal Reports ReportDocument will allow you to have the report automatically use the active connection string for the rest of the application (as in previous posts). In this case, the report is created using a method that is triggered by clicking a button on a form. The log on information must be applied to each table in the ReportDocument.

        Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
            Dim crReportDocument As ReportDocument
            crReportDocument = New ReportDocument
            crReportDocument.Load(<<name of reportdocument>>)

            Dim sConn As SqlConnectionStringBuilder = New SqlConnectionStringBuilder(<<connection string>>)

            Dim tables As CrystalDecisions.CrystalReports.Engine.Tables = crReportDocument.Database.Tables

            For Each table As CrystalDecisions.CrystalReports.Engine.Table In tables
                Dim tableLogOnInfo As CrystalDecisions.Shared.TableLogOnInfo = table.LogOnInfo
                tableLogOnInfo.ConnectionInfo.ServerName = sConn.DataSource
                tableLogOnInfo.ConnectionInfo.DatabaseName = sConn.InitialCatalog
                tableLogOnInfo.ConnectionInfo.IntegratedSecurity = True
                table.ApplyLogOnInfo(tableLogOnInfo)
            Next

            ' ...

       End Sub
Posted on

Classics of Software Engineering

software engineering books

Even though I have been writing programs for most of my life, that does not mean that my programs have always been written well. Only following the standard prohibitions on spaghetti code and documenting well does not a good program make.

The best advice I ever got about writing programs was to read two books:

1. The Pragmatic Programmer, by Andy Hunt and Dave Thomas
2. Code Complete, 2nd Edition, by Steve McConnell

After applying the techniques from these books, your programs will be much easier to maintain, and much more efficient.

A third book that is also quite helpful is Design Patterns: Elements of Reusable Object-Oriented Software by Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides (aka the Gang of Four).

These books are all available at Amazon.com in paper or Kindle format.