StreamReader handles text files. We read a text file in VB.NET by Using StreamReader. This will correctly dispose of system resources and make code simpler.
The best way to use StreamReader requires some special syntax. The Using-keyword allows you to automate disposal of the system resources, which is critical for performance and stability.
Example. The example reads the first line from file.txt in the local directory. You need to add a text file called "file.txt" and include it in the build directory ("Copy if newer").
Start Look at how the Using-statement is formed to create the StreamReader. This is the most common usage pattern for StreamReader.
Also We include the System.IO namespace at the top, with the line "Imports System.IO". This is important to compile the program.
Imports System.IO
Module Module1
Sub Main()
' Store the line in this String.
Dim line As String
' Create new StreamReader instance with Using block.Using reader As StreamReader = New StreamReader("file.txt")
' Read one line from file
line = reader.ReadLine
End Using
' Write the line we read from "file.txt"
Console.WriteLine(line)
End Sub
End Module(Contents of file.)
Example 2. This example starts off by declaring a new List(Of String). This instance is a generic List. The Using-statement is used next, and it opens the "file.txt" file.
Also There is a local line variable declared, which will store each line as it is read.
Info Before the loop begins, we read the first line. Then we enter a Do While loop, which continues until the last line read is Nothing.
Detail At the end of the program, I inserted a debugger breakpoint to show the contents of the List.
And I found that there were two string elements, containing Line 1 and Line 2 of the text file we read.
Imports System.IO
Module Module1
Sub Main()
' We need to read into this List.
Dim list As New List(Of String)
' Open file.txt with the Using statement.Using r As StreamReader = New StreamReader("file.txt")
' Store contents in this String.
Dim line As String
' Read first line.
line = r.ReadLine
' Loop over each line in file, While list is Not Nothing.Do While (Not line Is Nothing)
' Add this line to list.
list.Add(line)
' Display to console.
Console.WriteLine(line)
' Read in the next line.
line = r.ReadLine
Loop
End Using
End Sub
End Module
ReadToEnd. The StreamReader type can do more than just read lines. It can read an entire file into a string at once. Consider using the ReadToEnd Function.
Summary. Here we saw how to use the Using-statement in VB.NET, along with StreamReader to read in lines from text files. My experience is that StreamReader is well-performing.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Mar 21, 2023 (edit).