File Input/Output (I/O)

Tonga Institute of Higher Education

Working with Files and Directories

Programs often work with filesChanging files or directoriesGetting information about file or directoryGetting data form a file or directorySaving data in a file or directory

System.IO Namespace

The System.IO namespace contains many classes we can use to work with files and directoriesDirectoryInfoFileInfoStreamReaderStreamWriter

DirectoryInfo Contains methods for working with directories.

DirectoryInfo Properties

Exists - Gets a value indicating whether the directory exists.

FullName - Gets the full path of the directory or file.

Name - Gets the name of this DirectoryInfo instance.

Parent - Gets the parent directory of a specified subdirectory.

Root - Gets the root portion of a path.

DirectoryInfo Methods Create - Creates a directory CreateSubdirectory - Creates a subdirectory or

subdirectories on the specified path. Delete - Deletes a DirectoryInfo and its contents from a

path. GetDirectories - Returns the subdirectories of the current

directory. GetFiles - Retrieves an array of FileInfo objects. MoveTo - Moves a DirectoryInfo instance and its

contents to a new path. Refresh - Refreshes the state of the object. ToString - Returns the original path that was passed by

the user.

Demonstration

DirectoryInfo

FileInfo Contains methods for working with files.

FileInfo Properties Attributes - Gets or sets the FileAttributes of the

current FileSystemInfo. Directory - Gets an instance of the parent

directory DirectoryName - Gets a string representing the

directory's full path. Exists - Gets a value indicating whether a file

exists. Extension - Gets the string representing the

extension part of the file. FullName - Gets the full path of the directory or file Length - Gets the size of the current file. Name - Gets the name of the file.

FileInfo Methods AppendText - Creates a StreamWriter that appends text to

the file represented by this instance of the FileInfo. CopyTo - Copies an existing file to a new file. Create - Creates a file. CreateText - Creates a StreamWriter that writes a new text

file. Delete - Permanently deletes a file. MoveTo - Moves a specified file to a new location, providing

the option to specify a new file name. Open - Opens a file with various read/write and sharing

privileges. OpenText - Creates a StreamReader with UTF8 encoding

that reads from an existing text file. Refresh - Refreshes the state of the object. ToString - Returns the fully qualified path as a string.

FileInfo Collections

Demonstration

FileInfo

What is a Stream? A stream is a sequence of data Streams are used to move data from one place to another In our computer:

You can read from streams. Reading is the transfer of data from a stream into a data structure, such as a variable.

You can write to streams. Writing is the transfer of data from a data structure, such as a variable, into a stream.

Data SourceDestinationStream

Writing and Reading Streams

StreamReader – Object allows program to read data from a file using a stream.

StreamWriter – Object allows program to write data to a file using a stream.

StreamReader Allows a program to read characters from a file

Name of the filethat will be read

Loads 1 line

Always close the file. Close releases any resources used by the system

StreamReader 2

The end of the file is reachedwhen line is nothing

Demonstration

StreamReader

StreamWriter Allows a program to write characters to a file

WriteLine includesa carriage return

Name of the filethat will be written

Close releases any resourcesused by the system

Demonstration

StreamWriter

Handles situationwhen file not found

File I/O Exceptions Often, errors occur when file I/O statements are used.

The name of the file is changed A directory is deleted The location of a file is incorrect

File I/O exceptions allow the program to handle certain errors.

Causesan error

Handles othersituations

Common File I/O Exceptions DirectoryNotFoundException - The exception that is

thrown when part of a file or directory cannot be found. FileNotFoundException The exception that is thrown

when an attempt to access a file that does not exist on disk fails.

EndOfStreamException - The exception that is thrown when reading is attempted past the end of a stream.

PathTooLongException The exception that is thrown when a pathname or filename is longer than the system-defined maximum length.

SecurityException - The caller does not have the required permission.

Demonstration

File I/O Exceptions

File Dialog Boxes

Often, a user needs a GUI to select a file to open or enter the name and location of a file to save

OpenDialogBox - Provides GUI for selecting a file to open

SaveDialogBox - Provides GUI for inputting the name and location of a file to save

Open Dialog Box

Provides GUI for selecting a file to open

Open Dialog Box GUI

The properties can be set using the GUI

There are manyproperties

Open Dialog Box GUI Code But code must be used to display it and handle

what the user does with it.

Demonstration

OpenFileDialog with GUI and Code

Using OpenFileDialog with Only Code Many developers prefer to create source code when

using the OpenFileDialog box This allows the developer to see everything they have

done

Demonstration

OpenFileDialog with Only Code

Save Dialog Box

Provides GUI for inputting the name and location of a file to save

Save Dialog Box GUI

The properties can be set using the GUI

There are manyproperties

Save Dialog Box GUI Code But code must be used to display it and handle

what the user does with it.

Demonstration

SaveFileDialog with GUI and Code

Using SaveFileDialog with Only Code Many developers prefer to create source code when

using the OpenFileDialog box This allows the developer to see everything they have

done

Demonstration

SaveFileDialog with Only Code