Visual Basic 1002005 [A Developers Notebook] [Electronic resources] نسخه متنی

6.7. Unleash the Console

.NET 1.0 introduced the
Console class to give programmers a convenient way
to build simple command-line applications. The first version of the
Console was fairly rudimentary, with little more
than basic methods like Write( ),
WriteLine( ), Read( ), and
ReadLine( ). In .NET 2.0, new features have been
added, allowing you to clear the window, change foreground and
background colors, alter the size of the window, and handle special
keys.

Note: At last, a Console class with keyboard-handling and
screen-writing features.

6.7.1. How do I do that?

The best way to learn the new features is to see them in action.
Example 6-7 shows a simple application,
ConsoleTest, which lets the user move a happy
face character around a console window, leaving a trail in its wake.
The application intercepts each key press, checks if an arrow key was
pressed, and ensures that the user doesn't move
outside of the bounds of the window.

Warning: In order for the advanced console features to work, you must disable
the Quick Console window. The Quick Console is a console window that
appears in the design environment, and it's too
lightweight to support features like reading keys, setting colors,
and copying characters. To disable it, select Tools
Options, make sure the
"Show all settings checkbox" is
checked, and select the Debugging
General tab. Then, turn
off the "Redirect all console output to the Quick
Console window."

Example 6-7. Advanced keyboard handling with the console

Module ConsoleTest
Private NewX, NewY, X, Y As Integer
Private BadGuyX, BadGuyY As Integer
Public Sub Main( )
' Create a 50 column x 20 line window.
Console.SetWindowSize(50, 20)
Console.SetBufferSize(50, 20)
' Set up the window.
Console.Title = "Move The Happy Face"
Console.CursorVisible = False
Console.BackgroundColor = ConsoleColor.DarkBlue
Console.Clear( )
' Display the happy face icon.
Console.ForegroundColor = ConsoleColor.Yellow
Console.SetCursorPosition(X, Y)
Console.Write("")
' Read key presses.
Dim KeyPress As ConsoleKey
Do
KeyPress = Console.ReadKey( ).Key
' If it's an arrow key, set the requested position.
Select Case KeyPress
Case ConsoleKey.LeftArrow
NewX -= 1
Case ConsoleKey.RightArrow
NewX += 1
Case ConsoleKey.UpArrow
NewY -= 1
Case ConsoleKey.DownArrow
NewY += 1
End Select
MoveToPosition( )
Loop While KeyPress <> ConsoleKey.Escape
' Return to normal.
Console.ResetColor( )
Console.Clear( )
End Sub
Private Sub MoveToPosition( )
' Check for an attempt to move off the screen.
If NewX = Console.WindowWidth Or NewX < 0 Or _
NewY = Console.WindowHeight Or NewY < 0 Then
' Reset the position.
NewY = Y
NewX = X
Console.Beep( )
Else
' Repaint the happy face in the new position.
Console.MoveBufferArea(X, Y, 1, 1, NewX, NewY)
' Draw the trail.
Console.SetCursorPosition(X, Y)
Console.Write("*")
' Update the position.
X = NewX
Y = NewY
Console.SetCursorPosition(0, 0)
End If
End Sub
End Module

To try this out, run the application and use the arrow keys to move
about. Figure 6-2 shows the output of a typical
ConsoleTest session.

Figure 6-2. A fancy console application

Some of the new Console methods used in
ConsoleTest include the following:

Clear( )

Erases
everything in the console window and positions the cursor in the
top-left corner.

SetCursorPosition( )

Moves the cursor to the designated x- and
y-coordinates (measured from the top-left corner). Once
you've moved to a new position, you can use
Console.Write( ) to display some characters there.

SetWindowSize( ) and SetBufferSize( )

Allow you to change the size of the window
(the visible area of the console) and the buffer (the scrollable area
of the console, which is equal to or greater than the window size).

ResetColor( )

Resets the foreground and background
colors to their defaults.

Beep( )

Plays a simple beep, which is often used to
indicate invalid input.

ReadKey( )

Reads just a single key press
and returns it as a ConsoleKeyInfo object. You can
use this object to easily tell what key was pressed (including
extended key presses like the arrow keys) and what other keys were
held down at the time (like Alt, Ctrl, or Shift).

MoveBufferArea( )

Copies a
portion of the console window to a new position, and erases the
original data. This method offers a high-performance way to move
content around the console.

The new Console properties include:

Title

Sets the window caption.

ForegroundColor

Sets the text color that will be used
the next time you use Console.Write( ) or
Console.WriteLine( ).

BackgroundColor

Sets the background color that will
be used the next time you use Console.Write( ) or
Console.WriteLine( ). To apply this background
color to the whole window at once, call Console.Clear() after you set the background color.

CursorVisible

Hides the blinking cursor when set to
False.

WindowHeight and WindowWidth

Returns or sets the dimensions of the
console window.

CursorLeft and CursorTop

Returns or moves the current cursor
position.

6.7.2. What about...

...reading a character from a specified position of the window?
Sadly, the new Console class provides no way to do this. That means
that if you wanted to extend the happy face example so that the user
must navigate through a maze of other characters, you would need to
store the position of every character in memory (which could get
tedious) in order to check the requested position after each key
press, and prevent the user from moving into a space occupied by
another character.

6.7.3. Where can I learn more?

To learn more about the new Console class and its
new properties and methods, look for the Console
and ConsoleKeyInfo classes in the MSDN help
library reference.