Application Configuration File

Sample Code to manage app.config

Dim strConfig As String
strConfig = System.Reflection.Assembly.GetExecutingAssembly().
CodeBase.Replace("file:///", "") + ".config"

Dim doc As XmlDocument = New System.Xml.XmlDocument()
doc.Load(strConfig)

' Get Node value
MessageBox.Show(doc.SelectSingleNode("descendant::
appSettings/add[@key='ConnectionString']").
Attributes("value").Value())

' Update Node value 
doc.SelectSingleNode("descendant::appSettings/
add[@key='ConnectionString']").Attributes("value").Value
= "This is new connection string"

System.Configuration Basics

The System.Configuration namespace provides the functionality for reading configuration files. Microsoft released an XML schema dictating the format for configuration files that can be read using the System.Configuration API, enabling the accessing object to automatically consume the configuration files. This way, you can allow configuration files to be read without having to develop a bunch of plumbing to read the file and find the desired setting. Multiple types of configuration files are relevant to .NET, but this article focuses exclusively on the configuration files containing application-specific settings.

The name and storage location of an application configuration file depends on the application type with which it is being used. A configuration file for an executable (.exe) is located in the same directory as the application. The file is the name of the application with a .config extension. For example, notepad.exe would have a configuration file of notepad.exe.config. A configuration file for an ASP.NET application is called web.config and is located in the root of the application's virtual directory.

appSettings Section

An application configuration file follows a specific XML schema. The appSettings section is a predefined section of the configuration file designed to make it very easy to retrieve a value based on a given name. This is the easiest way to add application-specific settings into an application configuration file. The appSettings section of the configuration file consists of a series of "add" elements with "key" and "value" attributes. While the appSettings section is predefined, it is not included in a configuration file by default and must be manually added. A simple example of a configuration file would be the following:

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VB.Net: Dynamic Usage Of Eventhandlers

VB.Net: Dynamic Usage Of Eventhandlers

WithEvents and Handles clause requires form us to declare the object variable and the event handler as we write our code, so linkage is created upon compilation. On the other hand, with AddHandler and RemoveHandler, linkage is created and removed at runtime, which is more flexible.

Let's assume that we want to load several MDI child forms, allowing each of them to be loaded only once, and of course to know when one of the child forms is closed. Since we have several forms to load we would like to use the AddHandler and RemoveHandler keywords so we can be flexible and write the minimal code we can.

Let's get dirty.

1. In each MDI child form we have to declare a public event.
Public Event FormClosed(ByVal f As Form)

2. In each MDI child form we have to use the Form_Closed method which handles the MyBase.Closed class and raise the FormClosed event.

Private Sub Form1_Closed(ByVal sender As Object, ByVal e As System.EventArgs) _
Handles MyBase.Closed
RaiseEvent FormClosed(Me)
End Sub

3. On our MDI form we need to declare two member variables. The first's of type Form and the second's type is ArrayList.
Private m_f(0) as Form
Private m_sLoadedChildForms As New ArrayList

4. We need to implement a method the will search the MDI child forms that are loaded. We'll also use this method when we unload the MDI child forms.

Private Function SearchChildForm(ByVal strSearchForm As String, _Optional ByVal idxEventHandler As Long = -1) As Long
Dim i As Long = 0
For i = 0 To m_sLoadedForms.Count - 1
If m_sLoadedForms.Item(i) = strSearchForm Then
Dim j As Long = 0
For j = m_f.GetLowerBound(0) To m_f.GetUpperBound(0)
If m_f(j).Name = strSearchForm Then idxEventHandler = j
Next j
Return i
End If
Next
Return -1
End Function

5. We need to implement a method to load the mdi child forms and use the SearchChildForm method in order not to load the same mdi child form second time.

Private Sub LoadChildForms(ByVal f As Form)
If m_f.GetUpperBound(0) > 0 Then
ReDim Preserve m_f(m_f.GetUpperBound(0) + 1)
End If
m_f(m_f.GetUpperBound(0)) = f I
f Not SearchChildForm(m_f(m_f.GetUpperBound(0)).Name()) >= 0 Then
m_f(m_f.GetUpperBound(0)).MdiParent = Me
AddHandler m_f(m_f.GetUpperBound(0)).Closed, _
AddressOf UnloadChildForm
m_f(m_f.GetUpperBound(0)).Show()
m_sLoadedChildForms.Add(m_f(m_f.GetUpperBound(0)).Name)
Else
If m_f.GetUpperBound(0) > 0 Then
ReDim Preserve m_f(m_f.GetUpperBound(0) - 1)
End If
End If
End Sub

6. At last we need to implement a method to take out our mdi child form from the array list so we can load it again if we want.

Private Sub UnloadForm(ByVal sender As System.Object, ByVal e As System.EventArgs)
Dim i As Long
Dim s As String = sender.GetType().Name
Dim IndexForEventHandler = -1
i = SearchChildForm(s, IndexForEventHandler)
If i >= 0 Then m_sLoadedForms.RemoveAt(i)
If IndexForEventHandler >= 0 Then
RemoveHandler m_f(IndexForEventHandler).Closed, AddressOf UnloadForm
m_f(IndexForEventHandler) = Nothing
End If
End Sub

About the Author:

Thomas is an experienced Visual Basic developer, with expertise of 7+ years developing financial applications. His main IT skills are VB, SQL, Crystal Reports - should you need a VB developer for your projects feel free to contact Thomas through his personal website at http://www.Kaloyani.com or through http://www.VBprofs.com

Read more articles by: Thomas Kaloyani

Article Source: www.iSnare.com

Read xml content by XmlDocument

This sample show, How to read xml content by use XmlDocument namespace.

You can see this link for xml sample content.

Sample Code

Dim m_xmld As XmlDocument
Dim m_nodelist As XmlNodeList
Dim m_node As XmlNode

'Create the XML Document
m_xmld = New XmlDocument()

'Load the Xml file
m_xmld.Load("YourPath\test.xml")

'Show all data in your xml
MessageBox.Show(m_xmld.OuterXml)


'Get the list of name nodes
m_nodelist = m_xmld.SelectNodes("/family/name")

'Loop through the nodes
For Each m_node In m_nodelist
'Get the Gender Attribute Value
Dim genderAttribute = m_node.Attributes.GetNamedItem("gender").Value

'Get the firstName Element Value
Dim firstNameValue = m_node.ChildNodes.Item(0).InnerText

'Get the lastName Element Value
Dim lastNameValue = m_node.ChildNodes.Item(1).InnerText

'Write Result to the Console
Console.Write("Gender: " & genderAttribute _
& " FirstName: " & firstNameValue & " LastName: " _
& lastNameValue)
Console.Write(vbCrLf)
Next

Read xml content to DataSet.

This sample show, How to read xml's content to dataset.

Use System.Xml and System.IO namespace.  
Imports System.Xml 
Imports System.IO


Sample XML




Sample Code

Dim ds As New DataSet
'  use filestream class to read xml content.
Dim streamRead As New System.IO.FileStream("C\test.xml",  _
System.IO.FileMode.Open)

'Dataset can read content from FileStream.
ds.ReadXml(streamRead) 

  '  Bind data to your control. 
DataGridView1.DataSource = ds.Tables(0)  

' Close FileStream object
streamRead.Close()


You will see you data in your data control.