MDBitz Development Resources

A common task when creating a form based windows application is to allow a user to save their information and to also load saved information. In this short tutorial I will show you the basic steps to save a form’s information to a file and then load up the contents of the saved file.

Saving a Form’s Data to a File

The process for saving data to a file is pretty straightforward in Visual Basic. They include opening up a writer to a specified file, writing the contents, and then closing the writer when completed.

1. Define and open your File Writer
   In this case we will utilize the StreamWriter class of the System.IO package. I will assume for these instructions that you have imported the System.IO library.

   Dim FileWriter As StreamWriter ' define the stream writer
   
   ' Open the File for writing
   FileWriter = New StreamWriter("c:\temp\sampleFile.txt", False)

2. Write the desired data to the file
   To write data to the file you can utilize the WriteLine function. In the case of forms you may want to write different data. For a text field saving the Text is appropriate while when using a check box or radio button you will want to save the Checked property.

    ' Save Component values
   FileWriter.WriteLine(textBox.Name & "|" & textBox.Text)
   FileWriter.WriteLine(comboBox.Name & "|" & comboBox.SelectedIndex.ToString())
   FileWriter.WriteLine(radioBtn.Name & "|" & radioBtn.Checked.ToString())

3. Close and Save your data to the File
   To complete your write you simply need to call Close on your writer. However if you want you can first call Flush to have the data written out. This step is optional however as the Close function will call Flush if needed.

    ' Save and Close File
   FileWriter.Flush() ' optional as close will flush
   FileWriter.Close()

Reading Data from a File

The process for reading information out of a File is similar to the writing process. First you want to open up the file, then you want to read a line of data, single character, or etc depending on how you are going to process the data until you reach the end. After you have read all the data you would lastly close the File.

1. Define and open your File Reader
   In this case we will utilize the StreamReader class of the System.IO package.

    Dim FileReader As StreamReader   ' define the File Reader
   FileReader = New StreamReader("c:\temp\sampleFile.txt", False)

2. Iterate until the End of File is reached

   Do Until FileReader.EndOfStream
       ' Processing Code goes here
   Loop

3. Read in and Process the File’s data
   In the below example we will read in the file’s contents 1 line at a time. To see the full example of how the data is processed please view the full source code below.

   'Read the next line
   prop = FileReader.ReadLine()

4. Close the File Reader
   After the loop close the FileReader as all the data has been read.

   FileReader.Close()

A complete sample Save and Write Class

For those that learn better by example below is a Simple Class that holds a complete example of saving data to a File from a Form in addition to loading the saved data from the form and setting the components to the correct state. The example contains basic error checking including validating that the saved file exists, however it does not validate the data in the file is of the correct format and not corrupted.

Imports System.IO
 
Public Class Form1
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        loadSavedData()
    End Sub
 
    Private Sub CloseButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CloseButton.Click
        Close() 'Close Application
    End Sub
 
    Private Sub LoadButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles LoadButton.Click
        loadSavedData()
    End Sub
 
    Private Sub loadSavedData()
 
        Dim FileReader As StreamReader   ' define the File Reader
        Dim prop(2) As String            ' define array of length 2

        ' Test if the Saved File exists
        If File.Exists("c:\temp\sampleFile.txt") Then
 
            'Open the File for reading
            FileReader = New StreamReader("c:\temp\sampleFile.txt", False)
 
            ' Continue until EOF reached
            Do Until FileReader.EndOfStream
 
                'Read the next line and split its value based on the | character
                prop = FileReader.ReadLine().Split("|")
 
                ' If TextBox Component set it's property
                If String.Equals(prop(0), textBox.Name) Then
 
                    textBox.Text = prop(1)
 
                    ' If ComboBox Component set it's property
                ElseIf String.Equals(prop(0), comboBox.Name) Then
 
                    comboBox.SelectedIndex = Integer.Parse(prop(1))
 
                    ' If RadioButton set if checked
                ElseIf String.Equals(prop(0), radioBtn.Name) Then
 
                    radioBtn.Checked = Boolean.Parse(prop(1))
 
                ElseIf String.Equals(prop(0), RadioButton1.Name) Then
 
                    RadioButton1.Checked = Boolean.Parse(prop(1))
 
                ElseIf String.Equals(prop(0), RadioButton2.Name) Then
 
                    RadioButton2.Checked = Boolean.Parse(prop(1))
 
                End If
 
            Loop
 
            ' close the file
            FileReader.Close()
 
        End If
 
    End Sub
 
    Private Sub SaveButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SaveButton.Click
 
        Dim FileWriter As StreamWriter ' define the stream writer

        ' Open the File for writing
        FileWriter = New StreamWriter("c:\temp\sampleFile.txt", False)
 
        ' Save Component values
        FileWriter.WriteLine(textBox.Name & "|" & textBox.Text)
        FileWriter.WriteLine(comboBox.Name & "|" & comboBox.SelectedIndex.ToString())
        FileWriter.WriteLine(radioBtn.Name & "|" & radioBtn.Checked.ToString())
        FileWriter.WriteLine(RadioButton1.Name & "|" & RadioButton1.Checked.ToString())
        FileWriter.WriteLine(RadioButton2.Name & "|" & RadioButton2.Checked.ToString())
 
        ' Save and Close File
        FileWriter.Flush() ' optional as close will flush
        FileWriter.Close()
    End Sub
End Class