VB2008从入门到精通(PDF格式英文版)-第77部分
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Dim newDate As String = _
dateSplit（0） & 〃。〃 & dateSplit（1） & 〃。〃 & dateSplit（2）
If _dates。Contains（newDate） Then
Continue Do
End If
_dates。Add（newDate）
retval。Append（newDate）
For c1 As Integer = 0 To 7
retval。Append（〃 〃 & splitUpText（c1））
Next
Else
_dates。Add（splitUpText（0））
retval。Append（lineOfText）
End If
Of all the problems we needed to solve； this is the trickiest； because it required multiple
pieces of code in multiple places。 The code processes the data stream and keeps a list of dates。
A date is added to the list only if the date does not exist in the list； which is checked using the
Contains（） method。 The lists expose this method to verify if the object being passed to it
equals one of the list members。 The way that most lists implement the method is to iterate each
method and call the Equals（） method。 The catch is that if you declare a custom type； the Equals（）
method defaults to verifying if one reference value equals another。 You would need to imple
ment a custom Equals（） method。
■Note When you encounter situations where you need to write multiple pieces of code in multiple places；
that is a sign that you are about to create code that is hard to maintain。 You should take a close look at the
code； and If possible； rewrite it。 Of course； this depends on a lot of factors。 So sometimes； you will need to
just write the code； test it； and hope that it works。
With the final solution； the console application TextProcessor is plete。 You could
process lotto。txt and get a correctly formatted data stream。
Piping Binary Data
When working with the console； for the most part； you will be transferring text data from one
process to another or from one file to another file。 However； when developing in ； working
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with text is not always the best choice。 A more efficient approach might be to store the data in
a binary format。
The easiest way to understand the difference between text data and binary data is to open
a binary file using a text editor； as shown in Figure 10…8。
Figure 10…8。 A binary file in a text editor
In Figure 10…8； you see just a bunch of funny characters with some text scattered throughout。
A binary file is different from a text file in that the format of a binary file is whatever the program
that reads and writes the binary data decides。 The advantage of using a binary file is that you
can create plex structures。 The disadvantage is that only the developer of the reader/writer
program knows what the file contains。
Binary files are not always smaller； but they are more efficient because you do not need to
parse and process the data。 For example； in the text…based lottery data stream reader； we needed
to parse every single line and then split the line of text into individual fields； which were then
parsed as integers and assigned to a variable。 Using a binary file； you only need to create a
binary type； and read or write that type。
In this section； we will continue with the example of the lottery…prediction application； but
this time； create it as a console application that converts a text data stream into a binary data
stream and then back to a text stream。 You’ll see how you can pipe the data from one stream to
another by sending it from one application to another application。 When we are finished
building this application； the following mand line will be valid。
type lotto。txt ｜ TextProcessor。exe ｜ Text2Binary。exe ｜ Binary2Text。exe
The mand line starts with generating a text data stream using the type mand。
The mand TextProcessor。exe generates a clean data stream that is then piped into
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270 CH AP T E R 1 0 ■ L E A R N I N G A B OU T P E R S IS TE N CE
Text2Binary。exe； which generates a binary data stream。 Finally； the binary data stream is
converted back into a text stream using Binary2Text。exe； which displays the data on the console。
The architecture of TextProcessor with its implementation of the IProcessor interface
and a general architecture of grabbing a file or console input/output stream worked。 However；
IProcessor is not usable for binary streams； so we need to implement a new interface and
architecture。
■Note The examples that follow illustrate a very mon situation where an architecture worked and the
ideas of the architecture could be applied in the new context。 What does not work is the actual implementa
tion of the original architecture。 You may be tempted to modify the working architecture so that it will work
with the new context。 As much as you would like to do that； don’t。 Often； the abstractions you create will
plicate the architecture and make the resulting code more plex。 Your challenge is to know when to
generalize an architecture and when to keep the ideas of an architecture but create a new implementation；
and you’ll learn this with experience。
Defining the Interfaces and Implementing the Shell
In ； the data streams are split into two types of streams： binary and text。 The TextWriter
and TextReader types are used to read text…based data streams。 As was demonstrated with the
StringReader type； when dealing with text…based streams； certain assumptions can be made；
such as being able to find new lines in the stream。 With binary data streams； no such assump
tions can be made。 Binary streams have their own format； which is known by only the program
doing the reading or writing。
The binary stream…based types can be used to process text data streams； but doing so would
require knowing the details of the data stream。 Remember that gives you a text…handling
system that understands the different Unicode code pages。 A Unicode code page is a specific
translation map。 If you decide to manipulate the text streams using binary stream types； you
are telling that you will manage the details of the Unicode code pages。 Of course； you
don’t want to do that； and thus should never mix data streams。 So； for our sample application；
we need to design two different interfaces： one to stream from text to binary and one to stream
from binary to text。
■Note For more information about Unicode and other text…related issues； see the MSDN “International Text
Display” section （http：//msdn2。microsoft。/en…us/library/ms776131。aspx）。
The following is the binary…to…text data stream interface； Binary2Text。IBinary2TextProcessor。
Imports System。IO
Public Interface IBinary2TextProcessor
Sub Process（ByVal input As Stream； ByVal output As TextWriter）
End Interface
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The IBinary2TextProcessor interface has a single method； Process（）； which has two param
eters： the binary stream and the text stream。 The implementation of IBinary2TextProcessor
would be responsible for reading the data from the binary stream and saving data to the
text stream。
The text…to…binary interface； IText2BinaryProcessor； follows a similar interface design；
except that the input and output stream types are reversed。
Imports System。IO
Public Interface IText2BinaryProcessor
Sub Process（ByVal input As TextReader； ByVal output As Stream）
End Interface
The idea of both interface declarations is to focus on transferring data from one stream
to another。
The shell for both data stream interfaces is very similar to the shell of the text…processing
stream； except that binary and text streams are involved。 The TextProcessor shell was respon
sible for knowing if the data stream was from the console or from a file。 When manipulating
binary streams； the source still needs to be ascertained； but instead of creating text streams；
binary streams are created。 If you understand the mechanics of using a text stream； you will
understand the mechanics of using a binary stream。
The following is the plete implementation of the text…to…binary bootstrap class。
Imports System。IO
Public Module Text2BinaryBootstrap
Public Sub DisplayHelp（）
Console。WriteLine（〃You need help？ Right now？〃）
End Sub
Public Sub Start（ByVal args As String（）； _
ByVal processor As IText2BinaryProcessor）
#If DEBUG_OUTPUT Then
Console。WriteLine（〃Argument count（〃 & args。Length & 〃）〃）
For Each argument As String In args
Console。WriteLine（〃Argument （〃 & argument & 〃）〃）
Next
#End If
Dim reader As TextReader = Nothing
