Special Edition Using ASP.Net

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:\Test\This\Out\Data.txt:

Dim strFilename as String strFilename = "C:\Test\This\Out\Data.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("VisitorFiles\MessageText.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