The File and StreamWriter Classes

The StreamWriter class implements a TextWriter for writing characters to a stream in a particular encoding. StreamWriter is designed for character output in a particular encoding, whereas subclasses of Stream are designed for byte input and output.

StreamWriter defaults to UTF8Encoding unless specified otherwise. UTF-8 handles Unicode characters correctly and gives consistent results on localized versions of the operating system.

This section creates a sample application that enables users to write a message, and then saves the message to a disk file so that other users can read the message. The code that reads and displays the message file appears in the preceding section.

Creating a Text File

Before any data can be written to the disk, a file must be created. This is done in the example with the File.CreateText() method. The following code shows how to create a file named C:TestThisOutData.txt:

Dim strFilename as String 
strFilename = “C:TestThisOutData.txt” 
File.CreateText( strFilename ) 

Writing Data to a Text File

The File.CreateText() method returns a StreamWriter object. This is then used to write the data to the newly created disk file. The following code uses an already opened StreamReader to write a string to disk:

writer.Write( strTextData ) 

Figure 5.9 shows the sample application in use. Listing 5.10 shows the code that makes it work.

Listing 5.10. Saving the Data That the User Entered into MessageText.txt

Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) 
    Dim writer As StreamWriter 
    Label1.Text = “” 

    Try 
        writer = _ 
           File.CreateText(Request.MapPath(“VisitorFilesMessageText.txt”)) 
        writer.Write(TextBox1.Text) 
        writer.Close() 
        Label1.Text = “File was written successfully” 
        TextBox1.Text = “” 
    Catch ex As Exception 
        Label1.Text = ex.Message 
    End Try 

End Sub