1 Prototyping for HCI Spring 2004 (Week 9) Jorge A. Toro

2 The Language File I/O

HCI430 – J.Toro3 File I/O Here, we will deal with text files only. In VB.NET, different classes handle different aspects of text files.  One class deals with reading files  One class deals with writing into files  Etc…

HCI430 – J.Toro4 File I/O IO.StreamReader class  Objects of this class are capable of reading text files IO.StreamWriter class  Objects of this class are capable of writing into text files

HCI430 – J.Toro5 File I/O IO.StreamReader class  Used for reading text files. Dim sr As IO.StreamReader sr = IO.File.OpenText(“hello.txt”) The object sr is created and opened the file “hello.txt” for reading

HCI430 – J.Toro6 File I/O If the file does not exist, you get an exception You need to “trap” the exception so the program does not fail.  There are different exceptions for different errors

HCI430 – J.Toro7 File I/O Reading text from the file  ReadLine method Reads one complete line of text from the file  Read method Reads at least one character from the file

HCI430 – J.Toro8 File I/O How do I know I finished reading a file?  Use the Peek method in the StreamReader  Peek returns -1 it you reached the end of the file

HCI430 – J.Toro9 File I/O Assume that there is a text file with the following format: id1 Last name1 First name1 Address1 City1 State1 Zip1... idN Last nameN First nameN AddressN CityN StateN ZipN

HCI430 – J.Toro10 File I/O Let’s traverse the file and display it into a textbox with multilines

HCI430 – J.Toro11 File I/O Dim sr As IO.StreamReader = IO.File.OpenText("members.txt") While sr.Peek <> -1 s = sr.ReadLine textbox1.text = textbox1.text & s End While sr.Close()

HCI430 – J.Toro12 File I/O IO.StreamWriter class  Used for writing into text files. Dim sr As IO.StreamWriter sr = IO.File.CreateText(“hello.txt”) The object sr creates a new file (“hello.txt”) for writing Dim sr As IO.StreamWriter sr = IO.File.AppendText(“hello.txt”) The object sr opens a file (“hello.txt”) for appending text to it

HCI430 – J.Toro13 File I/O Writing text into the file  WriteLine method Writes one complete line of text in the file and attaches a (character 13) at the end of it  Write method Writes at least one character in the file but does not attach a

HCI430 – J.Toro14 File I/O Important!!  Make sure you call the Close method after you are done using the file. Dim sr As IO.StreamReader = IO.File.OpenText("members.txt") While sr.Peek <> -1 s = sr.ReadLine textbox1.text = textbox1.text & s End While sr.Close() sr now closes the file