ENGR/CS 101 CS Session
Lecture 13



Log into Windows/ACENET (reboot if in
Linux)
Start Microsoft Visual Studio 2012 and open
the Substitution Cipher Project
Has everyone finished the program from last
class so that it can encipher and decipher
using the Vigenere cipher?
Lecture 13
ENGR/CS 101 Computer Science Session
1
Outline

Problem: Loading messages from and saving
messages to files


Lecture 13
File streams
Open/Save Dialogs
ENGR/CS 101 Computer Science Session
2
Problem: Loading & Saving
Messages



Typing in long messages is tedious and error
prone. Also, message often come in textfiles.
Keeping a record of the resulting messages
would require writing down the messages on
a piece of paper, also tedious and error
prone.
We would like to enhance our project to be
able to read messages from a file and write
the results to a textfile.
Lecture 13
ENGR/CS 101 Computer Science Session
3
GUI Interface

Add four buttons to the GUI to be clicked to
do the following actions. Set their Name
properties as indicated





Load Plaintext - loadPlainBtn
Save Plaintext - savePlainBtn
Load Ciphertext - loadCipherBtn
Save Ciphertext - saveCipherBtn
Style them however you like.
Lecture 13
ENGR/CS 101 Computer Science Session
4
Reading from a File



Double-click on the Load Plaintext button.
The handler for this button must read a
plaintext message from a file and load it into
the plaintext box.
A file stream is a program object that is
opened (i.e., attached to a physical file) when
it is created. StreamReader objects are
used to read data from a file.
Lecture 13
ENGR/CS 101 Computer Science Session
5
OpenFileDialog


An OpenFileDialog is
the window that pops
up when a user wants
to open a file.
It is used to connect a
file stream to a
physical file.
Lecture 13
ENGR/CS 101 Computer Science Session
6
OpenFileDialog

An OpenFileDialog is declared and initialized
as follows:
OpenFileDialog fileChooser = new OpenFileDialog();

To make the dialog pop up and get the file
name from the user, call the ShowDialog
method and save the result in a DialogResult
variable
DialogResult result = fileChooser.ShowDialog();
Lecture 13
ENGR/CS 101 Computer Science Session
7
OpenFileDialog

If a user clicks on the Cancel button, our
application must go back to waiting, so we
test the DialogResult.
// Check if user clicked Cancel
if (result == DialogResult.Cancel)
{
return; // Go back to waiting
}
Lecture 13
ENGR/CS 101 Computer Science Session
8
StreamReader

Now we create a StreamReader object using
the chosen file name, then read the entire file
into the plaintext box.
// Open (attach) the file chosen in the dialog
StreamReader fileInput =
new StreamReader (fileChooser.FileName);
// Read entire file contents into plaintext box
plaintextBox.Text = fileInput.ReadToEnd();
Lecture 13
ENGR/CS 101 Computer Science Session
9
StreamReader

The squiggly red lines under
"StreamReader", means that the program
needs to import the library that defines
StreamReader. Do this by right-clicking on
"StreamReader", selecting "Resolve", then
"using System.IO".
Lecture 13
ENGR/CS 101 Computer Science Session
10
StreamReader

All file streams should be closed (i.e.
detached from the physical file).
fileInput.Close(); // Detach the physical file

Finally, the ciphertext box should be cleared,
since whatever was in it is no longer related
to what is now in the plaintext box
ciphertextBox.Text = ""; // Clear ciphertext box
Lecture 13
ENGR/CS 101 Computer Science Session
11
In-class Exercise, Part 1


Test the program. Create a message file by
using FILE->New, select Text File. Then use
FILE->Save As to give it a name like
"message.txt" and put it in the project folder.
Click on the Load Plaintext button. An
OpenFileDialog should pop up. Browse to
your message file and click Open. The text in
the file should appear in the plaintext box.
Lecture 13
ENGR/CS 101 Computer Science Session
12
In-class Exercise, Part 1



Double-click on the Load Ciphertext button
Write the click handler code for this button. It
is almost exactly the same as the code for
the Load Plaintext button. The only
difference is that the file contents are put into
the ciphertext box (instead of the plaintext
box) and the plaintext box is cleared.
Test you program again.
Lecture 13
ENGR/CS 101 Computer Science Session
13
Writing to a File



Double-click on the Save Ciphertext button
This handler must write a ciphertext
message to a file.
StreamWriter objects are used to write data
to a file.
Lecture 13
ENGR/CS 101 Computer Science Session
14
SaveFileDialog

Getting a file name for saving a file is done
with a SaveFileDialog. It works exactly the
same way as the OpenFileDialog for getting a
file name from the user. (I.e., it is the same
code with SaveFileDialog instead of
OpenFileDialog.)
Lecture 13
ENGR/CS 101 Computer Science Session
15
StreamWriter

Now we create a StreamWriter object using
the chosen file name, then write the Text of
the ciphertext box to the file:
// Open (attach) the file chosen in the dialog
StreamWriter fileOutput =
new StreamWriter (fileChooser.FileName);
// Write ciphertext to file
fileOutput.WriteLine (ciphertextBox.Text);
fileOutput.Close();
// Detach the physical file
Lecture 13
ENGR/CS 101 Computer Science Session
16
In-class Exercise, Part 2


Test the program. After loading a plaintext
message and enciphering it, click on the Save
Ciphertext button. A SaveFileDialog should pop
up. Type in a file name like "secret.txt", make
sure it will be saved into the project folder, and
click Save.
You can look at the saved file by using FILE >Open->File.
Lecture 13
ENGR/CS 101 Computer Science Session
17
In-class Exercise, Part 2


Double-click on the Save Plaintext button
and write the click handler for it.
It is almost exactly the same as the code
for the Save Ciphertext button. The only
difference is that plaintextBox.Text is
saved to the file instead.
Lecture 13
ENGR/CS 101 Computer Science Session
18