1. Sequential Input and Output using Text Files
Text File I/O

2. Open and Save File Dialogs
Using pre-built standard dialogs to select files to be opened and saved

3. Caveat
These dialogs were designed to use in Windows GUI applications rather than console apps
To make them work with console applications:
You must add a reference to System.Windows.Forms (see next slide)
Add a using statement for the System.Windows.Forms namespace
Add the compiler attribute [STAThread] to the Main method in your console application

4. Adding a Reference

5. OpenFileDialog
Multiform Applications
November 10, 2018

6. OpenFileDialog Example
Create dialog instance
Caption for the dialog
Filter: limits which files show in the dialog
If the user clicked OK in the dialog, process the selected file
When dialog first opens, initial directory is folder where app’s .exe is found
Filter contains sequences of “description|*.ext” where “description” is a phrase that will be shown describing what is being shown and “*.ext” specifies which file extensions are to be shown
Multiform Applications
November 10, 2018

7. OpenFileDialog Example
Caption
Initial Directory
Filter
Only .txt files shown
Dropdown filter ComboBox Expanded
Multiform Applications
November 10, 2018

8. SaveFileDialog
Multiform Applications
November 10, 2018

9. SaveFileDialog Example
Create instance
Set initial directory, caption, and filters
Display dialog, and, if not cancelled by user, process the selected file
Multiform Applications
November 10, 2018

10. Designate a Relative Path to file

11. Folder Structure

12. SaveFileDialog Example
Caption
Initial Directory
Only *.txt files shown
Filter
Multiform Applications
November 10, 2018

13. Simple Text File I/O Simple reading and writing from/to a Text File
Multiform Applications
November 10, 2018

14. Text File I/O
The StreamReader and StreamWriter classes are provided by .NET for simple text file I/O
They must be opened before the first I/O operation and closed after the last I/O operation
Failure to close a file may result in loss of data so it is important to close a file after its last I/O operation
The OpenFileDialog and SaveFileDialog may be used to help to associate actual files with StreamReader and StreamWriter objects in a C# program
Multiform Applications
November 10, 2018

15. Opening the StreamReader
StreamReader constructor takes a string FileName
This shows opening a StreamReader object associated with an existing file selected with an OpenFileDialog.
Note: this operation could fail for a variety of reasons, so it should be in a try/catch.
Multiform Applications
November 10, 2018

16. Closing the StreamReader
Close the StreamReader – if we successfully opened it
Note that this code is in the Finally block since we want to close the file even if an exception occurred in reading data from the file
Multiform Applications
November 10, 2018

17. Reading From a StreamReader
Read one line of data from the StreamReader
The rest of the while loop processes the data but is unrelated to reading from the StreamReader
This file is comma-delimited, but that does not always apply in other cases
While there is more data …
Multiform Applications
November 10, 2018

18. Putting it all together …
Array of String
Multiform Applications
November 10, 2018

19. Opening a StreamWriter for Output
File is an output only file
File Mode – see next slide
File name from the dialog
In a try block
FileMode.Create says if the file does not already exist, create it.
If the file does exist, it will be erased and replaced by the new file.
Multiform Applications
November 10, 2018

20. FileMode Member name Description CreateNew Create Open OpenOrCreate
Create a new file. This requires Write access. If the file already exists, an IOException is thrown.
Create
Create a new file. If the file already exists, it will be overwritten. Requires Write access.
Open
Open an existing file. A FileNotFoundException is thrown if the file does not exist.
OpenOrCreate
Specifies that the operating system should open a file if it exists; otherwise, a new file should be created.
Truncate
Specifies that the operating system should open an existing file. Once opened, the file should be truncated so that its size is zero bytes. Attempts to read from a file opened with Truncate cause an exception.
Append
Opens the file if it exists and seeks to the end of the file, or creates a new file.

21. FileAccess Member name Description Read Write ReadWrite
Read access to the file. Data can be read from the file. Combine with Write for read/write access.
Write
Write access to the file. Data can be written to the file. Combine with Read for read/write access.
ReadWrite
Read and write access to the file. Data can be written to and read from the file.

22. Writing data to a StreamWriter
Write one line of data to the output file; note that fields in the data are “comma-delimited” as a result of this WriteLine
Multiform Applications
November 10, 2018

23. Closing the File after Writing
If the file was opened successfully, close it even if an I/O exception was thrown during the output operations
Multiform Applications
November 10, 2018

24. Putting it all together for output
Multiform Applications
November 10, 2018

25. Reading an Entire Text File
Verify that the file with this name exists
Attempt to open the file
Read the entire file into a single string variable
The above code should be in a try block since many exceptions are possible