This tutorial will show you how to develop a voting/polling system in a Windows Form with the use of XML and LINQ, using VB.
Polling systems can be extremely useful for capturing opinions or current trends. In this tutorial, we will look at how we can create a Windows Form to build a voting system where users can vote who is their favorite Presidentail Candidate, and then see the current results. We will be using an XML file to store the data. We will start by creating the structure of the XML file:
<?xml version="1.0" encoding="utf-8"?>
<Poll>
<Vote>
<Choice>Obama</Choice> </Vote> <Vote>
<Choice>McCain</Choice> </Vote> |
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Next, we can design our Form; we will have a label citing the question, and then the two options as Radio Buttons, and then a button to submit the vote. All of these controls can be grouped together. And then underneath, we can put another button to show current results of the poll, and a label to output the results.
Once we have designed our form, we can double-click on the Submit button to create a handler for it in the code-behind:
Private Sub butSubmit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles butSubmit.Click
If radMcCain.Checked = True Then
submitVote("McCain") ElseIf radObama.Checked = True Then
submitVote("Obama") End If |
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On button click, we check to see which option has been chosen, and then we call a method to commit the vote to the XML file. The submitVote method looks something like this:
Private Sub submitVote(ByVal theVote As String)
Try
Dim xmlDoc As XDocument = XDocument.Load("Poll.xml")
xmlDoc.Element("Poll").Add(New XElement("Vote", New XElement("Choice", theVote)))
xmlDoc.Save("Poll.xml")
lblResults.Text = "Thank you for your vote."
readXML() Catch
lblResults.Text = "Sorry, unable to process request. Please try again." End Try |
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Here, we are making use of a Try..Catch to try and reduce errors shown to the user. We are then opening the XML document and using LINQ to add a new element to it, saving the newly-cast vote into the document. Finally, we call the readXML method to output current results to the form:
Private Sub readXML()
Dim xmlDoc As XDocument = XDocument.Load("Poll.xml") Dim votes = From vote In xmlDoc.Descendants("Vote") _
Select Vote = vote.Element("Choice").Value Dim mCount As Integer Dim oCount As Integer mCount = 0 oCount = 0 For Each vote In votes
If vote = "McCain" Then
mCount += 1 ElseIf vote = "Obama" Then
oCount += 1 End If Next vote Dim theTotal As Double theTotal = mCount + oCount Dim mPercent As Double Dim oPercent As Double mPercent = (mCount / theTotal) * 100 oPercent = (oCount / theTotal) * 100 lblResults.Text = "McCain: " & mCount & " votes (" & mPercent & "%)." & Constants.vbLf lblResults.Text = lblResults.Text & "Obama: " & oCount & " votes (" & oPercent & "%)." & Constants.vbLf + Constants.vbLf |
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This method also makes use of LINQ to select all data from the XML file and then loop through it to count all votes for each candidate. Then we perform a simple calculation to determine the percentage of votes for each. Finally, we output the results to the form.
The entire code-behind will look something like this:
Public Class Form1
Private Sub butSubmit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles butSubmit.Click
If radMcCain.Checked = True Then
submitVote("McCain") ElseIf radObama.Checked = True Then
submitVote("Obama") End If End Sub Private Sub submitVote(ByVal theVote As String)
Try
Dim xmlDoc As XDocument = XDocument.Load("Poll.xml")
xmlDoc.Element("Poll").Add(New XElement("Vote", New XElement("Choice", theVote)))
xmlDoc.Save("Poll.xml")
lblResults.Text = "Thank you for your vote."
readXML() Catch
lblResults.Text = "Sorry, unable to process request. Please try again." End Try End Sub Private Sub readXML()
Dim xmlDoc As XDocument = XDocument.Load("Poll.xml") Dim votes = From vote In xmlDoc.Descendants("Vote") _
Select Vote = vote.Element("Choice").Value Dim mCount As Integer Dim oCount As Integer mCount = 0 oCount = 0 For Each vote In votes
If vote = "McCain" Then
mCount += 1 ElseIf vote = "Obama" Then
oCount += 1 End If Next vote Dim theTotal As Double theTotal = mCount + oCount Dim mPercent As Double Dim oPercent As Double mPercent = (mCount / theTotal) * 100 oPercent = (oCount / theTotal) * 100 lblResults.Text = "McCain: " & mCount & " votes (" & mPercent & "%)." & Constants.vbLf lblResults.Text = lblResults.Text & "Obama: " & oCount & " votes (" & oPercent & "%)." & Constants.vbLf + Constants.vbLf End Sub Private Sub butResults_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles butResults.Click
readXML() End Sub |
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