How to generate log file with Delegate and Event VB.NET

A delegate declaration defines a reference type that can be used to encapsulate a method with a specific signature. A delegate instance encapsulates a static or an instance method. Delegates are roughly similar to function pointers in C++; however, delegates are type-safe and secure.

This example demonstrates how to generate log file with Delegate and Event technique.

A delegate declaration defines a reference type that can be used to encapsulate a method with a specific signature. A delegate instance encapsulates a static or an instance method. Delegates are roughly similar to function pointers in C++; however, delegates are type-safe and secure.

Event represents the state of an event, such as the element in which the event occurred, the state of the keyboard keys, the location of the mouse, and the state of the mouse buttons.

First, you will need to import the System.IO namespace.

The System.IO namespace contains the StreamWriter and File Classes.

Imports System.IO

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The System.IO namespace contains types that allow reading and writing to files and data streams, and types that provide basic file and directory support.

We use the button1_Click event to do the work.
Click the button Generate Log File ,System will generate a log file in folder log which locates in root directory. The code as follows.

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnGeneratelog.Click Client.Run(txtKey.Text.Trim(), Server.MapPath("log")) End Sub

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Add two custom class Client and UserInputMoniter in the project. The code as follows.

Imports System Imports System.IO Public Class Client Private Shared path As String = "" Public Shared Sub Run(ByVal key As String, ByVal strpath As String) path = strpath Dim monitor As New UserInputMoniter() Dim a As New Client(monitor) monitor.Run(key) End Sub Private Sub GenerateLog(ByVal sender As Object, ByVal e As EventArgs) Dim writer As StreamWriter = Nothing Dim strPath As String = path + "\log.ini" Try If File.Exists(strPath) Then File.Delete(strPath) End If Try writer = File.AppendText(strPath) writer.WriteLine("Test log.") Finally writer.Dispose() End Try Catch ex As Exception Throw New Exception(ex.Message) Finally writer.Close() writer.Dispose() End Try End Sub Sub New(ByVal m As UserInputMoniter) AddHandler m.OnUserRequest, AddressOf Me.GenerateLog End Sub End Class Imports System '/ <summary> '/ UserInputMoniter '/ </summary> Public Class UserInputMoniter Delegate Sub UserRequest(ByVal sender As Object, ByVal e As EventArgs) Public Event OnUserRequest As UserRequest Public Sub Run(ByVal key As String) If key.Trim() = "h" Then RaiseEvent OnUserRequest(Me, New EventArgs()) End If End Sub End Class

The front end DelegateEventVB.aspx page looks something like this:

<table> <tr> <td colspan="2" style="text-align: left"> Information: <span style="color: #ff3333">If the KeyValue is 'h' ,click the follow button will generate log file in the folder log which locate in root directory.</span></td> </tr> <tr> <td style="width: 100px; text-align: right;"> <asp:Label ID="lblKeyValue" runat="server" Text="KeyValue:"></asp:Label></td> <td style="width: 100px"> <asp:TextBox ID="txtKey" runat="server"></asp:TextBox></td> </tr> <tr> <td colspan="2"> <asp:Button ID="btnGeneratelog" runat="server" OnClick="Button1_Click" Text="Generate Log File" /></td> </tr> </table>

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The flow for the code behind page is as follows.

Partial Class _Default Inherits System.Web.UI.Page Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnGeneratelog.Click Client.Run(txtKey.Text.Trim(), Server.MapPath("log")) End Sub Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load End Sub End Class

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