How to pass ListBox selected item into file? - vb.net

Question

What I have:
Private Sub ChooseProgram_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ChooseProgram.SelectedIndexChanged
Dim curItem As String = ChooseProgram.SelectedItem.ToString()
End Sub
Private Sub Install_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Install.Click
Dim jhin As System.IO.StreamWriter
jhin = My.Computer.FileSystem.OpenTextFileWriter("C:\Temp\jhin.bat", True)
jhin.WriteLine("$program = " & curitem.string")
jhin.Close()
End Sub
I just want to write the string into the file.
How is that possible?
Thx for ur help!
Hannir
UPDATE:
' Ensure an item is selected
If ChooseProgram.SelectedItem Is Not Nothing Then
curItem = ChooseProgram.SelectedItem.ToString()
End If
I get an error here.
"The Is operator does not accept operands of type " integer " . The operands must be reference types, or permit types , NULL values ​​."
Really thx for ur quick help! #Pro Grammer
If you just click Install, and nothing is selected, it ends in an error. So is it possible to say "You need to select an item before" or the Install button is just clickable when selected an item?

Answer 1

For starters you have to move the declaration of the curItem variable out of the SelectedIndexChanged method, to what's called Class level.
As it stands your variable is accessible within your SelectedIndexChanged method only, whereas if you move it to class level it will be accessible by everything within that class (the class in this case is your Form). You then just modify the variable from your SelectedIndexChanged method.
Dim curItem As String = "" 'We'll start with an empty string.
Private Sub ChooseProgram_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ChooseProgram.SelectedIndexChanged
curItem = ChooseProgram.SelectedItem.ToString()
End Sub
Now you will be able to access the variable from your button and write it to a file.
The last thing you have to do is to close the StreamWriter that you create so that it will release the lock on the file. The easiest and best way to do so is wrapping it in an Using/End Using block.
Private Sub Install_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Install.Click
Using jhin As System.IO.StreamWriter = My.Computer.FileSystem.OpenTextFileWriter("C:\Temp\jhin.bat", True)
jhin.WriteLine("$program = " & curItem)
End Using
End Sub
EDIT:
To make your button clickable only when an item is selected, first set the button's Enabled property to False via the Property Window in the designer, then use this code in the SelectedIndexChanged event:
Install.Enabled = ChooseProgram.SelectedIndex >= 0
If ChooseProgram.SelectedIndex < 0 Then Return
curItem = ChooseProgram.SelectedItem.ToString()

Answer 2

This is one option:
Private Sub Install_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Install.Click
Dim curItem as String = ""
' Ensure an item is selected
If ChooseProgram.SelectedItem IsNot Nothing
curItem = ChooseProgram.SelectedItem.ToString()
End If
' Double checking valid input
If String.IsNullOrWhiteSpace(curItem) Then
' Handle empty input - Display message, etc
' Exit Sub (unless bat handles empty)
End If
Dim jhin As System.IO.StreamWriter
jhin = My.Computer.FileSystem.OpenTextFileWriter("C:\Temp\jhin.bat", True)
jhin.WriteLine("$program = " & curItem)
jhin.Close()
End Sub
Instead of using the ChooseProgram_SelectedIndexChanged event, you can deal with it from here, since you aren't performing any other actions in that method. If you wanted to still use that event, you would assign the string value into a field which could be accessed across the class. Check out Visual Vincent's answer for this example, and also of a Using block, which removes the need to call jhin.Close() manually and also provides a much clearer format