How to Open a Text File in VB .NET

The ability to open up a text file and read its contents can be very useful
to you in your programming life. You might have a text file containing quiz
questions and answers, for example. You could read the questions and answers
from a text file and create your own “Who wants to be a Millionaire”
game. Or you might want to save some data associated with your programme, and
then open it up again when the programme starts. Well see how to open up a text
file in VB .NET right now. In a later section, you’ll learn how to save data
to a text file.

Cretae a StreamReader

To open up a text file, you need to create something called a “StreamReader“.
This, as its name suggests, reads streams of text. The StreamReader is an object
available to System.IO. (Visual Studio 2015 users can miss out the System
part. This applies for all the code in this text files section.) You create
a StreamReader like this:

Dim FILE_NAME As String = “C:UsersOwnerDocumentstest.txt”

Dim objReader As New System.IO.StreamReader(
FILE_NAME )

The first line just sets up a string variable called FILE_NAME. We store the
path and name of our text file inside of the string variable:

= “C:UsersOwnerDocumentstest.txt”

We’re saying that there is a text file called test which is at the location
(path) “C:”.

You set up the StreamReader to be a variable, just like a String or
Integer variable. But we’re setting up this variable differently:

Dim objReader As New System.IO.StreamReader(
FILE_NAME )

We’ve called the variable objReader. Then, after the “As”
word comes “New“. This means “Create a New Object”.
The type of object we want to create is a StreamReader object:

System.IO.StreamReader

Sysytem is the main object. IO is an object within System. And
StreamReader is an object within IO.

StreamReader needs the name of a file to Read. This goes between a pair of
round brackets:

System.IO.StreamReader( FILE_NAME )

VB will then assign all of this to the variable called objReader. So
instead of assigning say 10 to an Integer variable, you are assigning
a StreamReader to a variable.

Read To End

But this won’t do you any good. We haven’t actually opened the text file yet.
We’ve just told VB where the text file is and what object to open it with. You
do the opening like this:

TextBox1.Text = objReader.ReadToEnd

Now that objReader is an object variable, it has its own properties and methods
available for use (in the same way that the textbox has a Text property).

One of the Methods available to our new StreamReader variable is the ReadToEnd
method. This will read the whole of your text, right to the end. We’re then
popping this in a textbox.

Let’s test all this theory out. Do the following:

• Start a new project
• Add a textbox to your new form, and just leave it on the default Name of
  Textbox1
• Set its MultiLine property to True
• Add a Button to your form
• Double click the button and add the following code for it:

Dim FILE_NAME As String = “C:UsersOwnerDocumentstest.txt”

Dim objReader As New System.IO.StreamReader(
FILE_NAME )

TextBox1.Text = objReader.ReadToEnd

objReader.Close()

The last line closes the StreamReader we set up. You have to close your stream
objects after you’ve used them, otherwise you’ll get errors messages.

When you’re done, run your programme and click your Button.

Unless you already have a file called test.txt at the location specified you’ll
get this error message popping up like this one: (You may see this error message
in a different format, depending on which version of Visual Studio you have.)

The last line spells it out clearly: Could not find file “C:UsersOwnerDocumentstest.txt”.
So we were trying to read a text file that doesn’t exist.

Does the File Exist?

You can, though, test to see if the file exists. If it does, you can open it;
if not, you can display an error message. Amend your code to this (the new lines
are in bold):

Dim FILE_NAME As String = “C:UsersOwnerDocumentstest.txt”

If System.IO.File.Exists(FILE_NAME) = True Then

Dim objReader As New System.IO.StreamReader(FILE_NAME)
TextBox1.Text = objReader.ReadToEnd
objReader.Close()

Else

MessageBox.Show(“File Does Not Exist”)

End If>

We’ve now wrapped up our code in an If Statement. The first line of the If
Statement is this:

If System.IO.File.Exists( FILE_NAME
) = True Then

This tests to see whether or not a file exists. Again, you start with System.IO.
Then you access another object of System.IO – the File object. This has
a method called Exists. In between the round brackets, you type the name
(or variable) of the file you want to check. The value returned will either
be True (if it does exists), or False (if it doesn’t).

If the file exist then we can go ahead and create our StreamReader; If it doesn’t,
we can display a error message for the user.

So that your programme will work, there is a file below called “test.txt”.
Download this to your computer and save it to your Documents folder. (Right
click the file and select Save Target As (IE), or Save Link As (Firefox):

When you have done that, run your programme again. Click the button once more,
and you should see the text from your file appear in the textbox. (If you get
the error message again, it means you haven’t copied the file to the right place.)

In the next part, we’ll see how to read the contents line by line, instead
of all in one go.

Learn how to read a text file line by line — >