Variable 'details' is used before it has been assigned a value. - vb.net

Question

Variable details is used before it has been assigned a value. What is the problem with details?
Option Explicit On
Imports System.Text
Imports System.IO
Public Class Main
Private SelectedItem As ListViewItem
Dim data As String
Dim strpriority As String
Dim task As String
Dim createdate As String
Dim duedate As String
Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
AddTask.Show()
Me.Hide()
End Sub
Private Sub HistoryToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles HistoryToolStripMenuItem.Click
History.Show()
Me.Hide()
End Sub
Private Sub Main_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim fpath As String
Dim splitdata
fpath = AppDomain.CurrentDomain.BaseDirectory
Dim filepath As String
filepath = fpath & "task.txt"
Dim details As String
details = My.Computer.FileSystem.ReadAllText(filepath)
splitdata = Split(details, vbCrLf)
Dim i As Integer
For i = 0 To UBound(splitdata)
lblTaskName.Items.Add(splitdata(i))
Next
lblTime.Enabled = True
Timer1.Interval = 10
Timer1.Enabled = True
lblDate.Text = DateTime.Now.ToString("dd MMMM yyyy")
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
lblTime.Text = TimeOfDay
End Sub
Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
End
End Sub
Private Sub btnRemove_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRemove.Click
If lblTaskName.SelectedItem = "" Then
MsgBox("Please select a record")
Else
If lblTaskName.Items.Count > 0 Then
If MessageBox.Show("Do you really want to delete this record?", "Delete", MessageBoxButtons.YesNo) = MsgBoxResult.Yes Then
lblTaskName.Items.Remove(lblTaskName.SelectedItem.ToString())
Else
MessageBox.Show("Operation Cancelled")
End If
End If
End If
Try
Dim fpath As String
fpath = AppDomain.CurrentDomain.BaseDirectory
Dim filepath As String
filepath = fpath & "task.txt"
Dim details As String
If lblTaskName.Items.Count > 0 Then
details = lblTaskName.Items(0)
Dim i As Integer
For i = 1 To lblTaskName.Items.Count - 1
details = details & vbCrLf & lblTaskName.Items(i)
Next
End If
My.Computer.FileSystem.WriteAllText(filepath, details, False)
Catch ex As Exception
MsgBox("Values Can't be inserted this time")
End Try
End Sub
Private Function filepaths() As String
Throw New NotImplementedException
End Function
End Class

Answer 1

The problem is in the btnRemove_Click method in this part:
Dim details As String
If lblTaskName.Items.Count > 0 Then
details = lblTaskName.Items(0)
If the condition evaluates to false, the details variable is used before it is initialized, because it is only set in the if block up to now.
I suppose you want to move the following line into the if block to solve the problem:
My.Computer.FileSystem.WriteAllText(filepath, details, False)
Alternatively, you can come up with a default value for details so that it is set in any case. For performance reasons, you can set the default value (e.g. a text or String.Empty) in an else branch:
Dim details As String
If lblTaskName.Items.Count > 0 Then
' ...
Else
details = "Default Value"
End If

Answer 2

You need to think through the flow of your program. Consider this code:
Dim details As String
If lblTaskName.Items.Count > 0 Then
details = lblTaskName.Items(0)
Dim i As Integer
For i = 1 To lblTaskName.Items.Count - 1
details = details & vbCrLf & lblTaskName.Items(i)
Next
End If
My.Computer.FileSystem.WriteAllText(filepath, details, False)
You declare the details variable at the top. Then you check that there is at least 1 item in the lblTaskName control. If that test passes, then you assign the first item to details. But what if that test doesn't pass? What if there are 0 items in the lblTaskName control? In that case, the interior of the If block never runs, and nothing ever gets stored in details. Then in the final line, you try to use the value of the details variable *outside of the If block. This is illegal because it may not have been assigned a value.
Perhaps you meant for that WriteAllText line to be inside of If block? Otherwise, you'll need to add an Else clause to your If statement to handle the case where there are 0 items in lblTaskName.
Aside from that, stylistically speaking, you should prefer to initialize variables at the time of declaration whenever possible. So for example, instead of writing:
Dim fpath As String
Dim splitdata
fpath = AppDomain.CurrentDomain.BaseDirectory
Dim filepath As String
filepath = fpath & "task.txt"
Dim details As String
details = My.Computer.FileSystem.ReadAllText(filepath)
splitdata = Split(details, vbCrLf)
write it as:
Dim fpath As String = AppDomain.CurrentDomain.BaseDirectory
Dim filepath As String = fpath & "task.txt"
Dim details As String = My.Computer.FileSystem.ReadAllText(filepath)
Dim splitdata() As String = Split(details, vbCrLf)
(I'm OCD, so I line up my equals signs. That part is totally optional.)
It doesn't make the code run any faster, but it does make it easier to read! More importantly, it decreases the potential for bugs.