Visual Basic Files | Lesson 1

The first thing to learn about files is how to manipulate directories with Visual Basic.

Type the following at the top of the code page of the form that you have created.

Imports System.IO

By using the Imports statement you will not need to type System.IO for each command that you will perform on files.

Next you could add a button on the form and double click it. You will use this button to test some of the routines in this lesson.

Type the following code into the code designer:

Public Function CheckforDirectory(ByVal DirectoryName As String) As Boolean

   Return Directory.Exists(DirectoryName)

End Function

Functions return a value to the calling procedure and subs just process the code and do not return any value. This function will return a true or false value to the next routine in this lesson. The boolean data type is a true or false value and is used extensively in most programs.

The only statement in this function will check if the directory exists or not and will return the boolean value of true or false to the calling routine.

Next, double click on the Check Directory button and add the following code:

Dim s as string = Me.txbDirectoryName.Text

Try
   If Me.CheckforDirectory(s) Then
MessageBox.Show("Directory already exists.")
   Else
Directory.CreateDirectory(s)
MessageBox.Show("Directory " & s & " was created.")
   End If
Catch ex As Exception
   MessageBox.Show("Cannot check for directory. Reason: " & ex.Message)
End Try

The first line initializes and sets the variable "s" as a string(text) and sets its value as the text entered in the textbox txbDirectoryName.

The Try...Catch...End Try block is an error checking function provided with Visual Basic to check your code for runtime errors. For instance if the variable s is null then it will throw an error. When it throws an error the code will move to the Catch statement and display the messagebox. ex is the variable being declared to use in case an error is caught. This messagebox will show the error message with the part of the statement: "ex.Message"

The If...Then...End If statement after the Try statement will check if the directory exists. If it does the program will display the message "Directory already exists." If the directory does not exist the program will move to the Else statement and create the directory and then display a messagebox that shows that the directory was created. To verify this, open up My Computer from the start button and navigate to the folder that was just created.

Don't be afraid to experiment with this code or any code that is on this site. For example you can change the variable s to MyDirectoryName or your favorite dog's name. You can also change the messages that are displayed in each of the messageboxes to whatever you like. Enjoy and have fun.

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