VB2008从入门到精通(PDF格式英文版)-第74部分
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mand to read piped data。 The only thing missing is the file that contains the data；
lotto。txt。 For the example； create a file called lotto。txt and add text such as the following；
where each line represents the date of the lottery draw； then the six lottery numbers； and then
the bonus number （you could also use the lotto。txt file included with this book’s download
able code）。
1970。01。10 7 8 12 17 32 40 24
1970。01。17 7 12 22 24 29 40 36
1970。01。24 16 22 25 27 30 35 24
1970。01。31 3 11 21 22 24 39 8
1970。02。07 2 5 11 16 18 38 37
Now run the following piping mand （open a mand prompt and navigate to
TextProcessorTextProcessorbinRelease from the Visual Basic Express base directory）：
type lotto。txt ｜ TextProcessor。exe
You should see the contents of lotto。txt。 If that is what you get； you have a successful
round…trip and have created all of the puzzle pieces。
REMEMBERING TO IMPLEMENT ALL THE PIECES
Some readers may argue that having an echo implemented in LottoTicketProcessor is the wrong
approach because there might be a munication failure among team members； leading to buggy code。
Also； you might miss implementing some code； creating bugs when there should not have been any。 Although
those risks are involved； this approach has important benefits； and there are ways to mitigate the risks。
One of the challenges for Visual Basic developers is knowing not only the language； but also the API。
This book will not talk about the API because you could die of old age before you read everything there is to
know about the API。
The API is vast； but you will not need to use all of the API all the time。 What you need to be aware
of are the general classes of the API。 What part of the API is used to read and write streams？ What part of the
API is used to create GUI elements？ This means you are not ever going to be an expert on all parts of the API；
although you might be an expert Visual Basic programmer and understand the general concepts。
When I understand a domain quite well； I develop using a bottom…up approach。 This works because I
know which interface and implementation need to talk to which other interface and implementation。 When I
don’t understand a domain fully； I develop using a top…down approach。 Using a top…down approach； I can figure
out what the pieces are in a simplified manner。 I create my echo program； which gives a plete round…trip
without getting bogged down in the details of the API。
Think of a bunch of guys putting together a barbecue grill。 They might look at the instructions； but more
likely； they will look at the parts and try to mentally fit the pieces together。 They might even put a couple of
pieces together to get an idea of what each piece does and how the overall grill should appear。 Once they
bee confident of their prototype； they build the real thing； which hopefully resembles a barbecue grill。
When you use this approach； what you are doing is building a mockup； proof of concept； or prototype。
Maybe two or three team members might help develop this prototype； but the fact that your code needs to be
declared as a prototype is extremely important。
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CH A PT E R 1 0 ■ L E A R N I N G A B O U T P E R S IS T E N CE 257
Visual Basic Express and the Visual Studio products help you in that they allow you to embed task markers。 Go
back to the source code example where LottoTicketProcessor was illustrated and look at the ment：
' TODO： Finish implementing the class
Notice TODO is in all capital letters。 That type of ment is special。 It is called a task and is tracked by
Visual Basic Express in the Task List window。 To open ments in the Task List window； select View Other
Windows Task List； and then select ments from the drop…down list at the top of the window。
This allows a team of developers to add markers throughout the entire code base； indicating what is done
and not done。 That way； you will not forget to do certain tasks。
Some other identifiers that you can use are HACK to identify some code that is not correct； but hacked in so
that it works； and UNDONE。 If you happen to be using a Visual Studio edition other than Express； you can define
your own ment identifiers。 For more information； see the MSDN article “Visual Studio How to： Create Custom
ment Tokens” （http：//msdn2。microsoft。/en…US/library/ekwz6akh（VS。80）。aspx）。
Implementing Stream Reading and Writing
Finishing the stream reading and writing means looking at the possible arguments that can be
given； and then implementing the code to process the arguments。 Here is the plete source
code for ReaderWriter。Bootstrap：
#Const DEBUG_OUTPUT = True
Imports System。IO
Public Module Bootstrap
Public Sub DisplayHelp（）
Console。WriteLine（〃You need help？ Right now？〃）
End Sub
Public Sub Start（ByVal args As String（）； ByVal processor As IProcessor）
#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
Dim writer As TextWriter = Nothing
If args。Length = 0 Then
reader = Console。In
writer = Console。Out
ElseIf args。Length = 1 Then
If args（0） = 〃…help〃 Then
Bootstrap。DisplayHelp（）
Return
End If
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258 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
reader = File。OpenText（args（0））
writer = Console。Out
ElseIf args。Length = 2 Then
If args（0） 〃…out〃 Then
Bootstrap。DisplayHelp（）
Return
End If
reader = Console。In
writer = File。CreateText（args（1））
ElseIf args。Length = 3 Then
If args（0） 〃…out〃 Then
Bootstrap。DisplayHelp（）
Return
End If
reader = File。OpenText（args（2））
writer = File。CreateText（args（1））
Else
Bootstrap。DisplayHelp（）
Return
End If
writer。Write（processor。Process（reader。ReadToEnd））
End Sub
End Module
In the code； before the first If block； the variables reader and writer are assigned to the
value Nothing； indicating that there is a reader and there is writer； but we don’t know whether
they will reference streams or files。 Then the If blocks go through the different binations
and variations of the mand…line arguments （see Table 10…1）。
The code follows a truth table approach； which could be considered following a set of
conditions and then acting on the conditions。 For example； a state could be defined as If A = X；
and B ！= Y then do C。 To process the mand…line arguments； we define all of the possible
states and then all of the possible resulting actions。
■Note By going through each and every variation of the mand…line arguments in a sequential manner；
I am ensuring that I am testing for each situation。 When running various tests and then acting on the tests；
you need to be explicit and redundant； because the code is easier to follow。 All too often； programmers take
shortcuts and miss a particular test； causing a bug that is extremely hard to track down。
The first If block tests if the argument count is zero； then the second tests if there is a
single argument； and so on。 Let’s look at the first test：
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CH A PT E R 1 0 ■ L E A R N I N G A B O U T P E R S IS T E N CE 259
If args。Length = 0 Then
reader = Console。In
writer = Console。Out
。。。
End If
Here； the source and destination of the lottery number data stream are the console input
and output streams。 The code assigns the reader and writer variables。
If the mand line had no arguments or if one of the mand…line argument tests has
been verified； the IProcessor implementation is called：
writer。Write（processor。Process（reader。ReadToEnd（）））
The code directly executes writer。Write（）； processor。Process（）； and
reader。ReadToEnd（）。 There is no verification of whether writer； processor； or reader point to
actual object instances。 There could be a case for adding code that verifies if processor references
an actual object instance；
