《VB2008从入门到精通(PDF格式英文版)》第121章

pieces　in　place；　and　when　called　will　seem　like　it　functions。　The　echo　part　es　in　when　the
end　piece　of　functionality　is　called　and　it　returns　the　data　that　was　sent　to　it。　In　essence；　the　end
piece　is　acting　like　an　echo。　The　cleverness　behind　the　echo　is　that　it　requires　no　implementa
tion；　yet　it　demonstrates　the　plete　flow　of　data　and　whether　that　data　flow　is　workable。　
The　echo　program　is　not　a　final　program。　The　echo　program　is　a　temporary　solution　for　an
intermediate　goal。　When　building　an　application　with　intermediate　goals；　you　are　using　an
iterative　development　technique。　The　iterations　are　not　visible　to　your　other　team　members
and　are　pletely　private。　However；　the　iterations　will　keep　you　focused　on　solving　a　problem；
rather　than　trying　to　implement　a　large　piece　of　code　that　you　will　not　be　able　to　fully　test　for
a　while。　
Test…driven　development；　for　the　most　part；　is　a　bottom…up　development　approach。　You
develop　a　core　piece　of　functionality；　test　it；　and　then　write　code　that　uses　the　tested　piece　of
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functionality。　But　sometimes　you　need　to　develop　in　a　top…down　fashion。　I　typically　develop
code　top…down　when　I　am　trying　to　nail　down　an　overall　architecture。　The　problem　with　devel
oping　top…down　is　that　you　don’t　yet　have　the　bottom　code。　In　other　words；　you　are　writing
code　with　no　working　code。　So　that　your　code　does　have　some　meaning；　you　develop　an　echo。
The　echo　solves　the　problem　of　working　code　and　allows　you　to　focus　on　getting　the　individual
pieces　to　fit　together。　Once　the　pieces　are　working；　and　the　echo　was　successful；　you　can　start
filling　in　the　implementations。　Some　developers　call　the　echo　a mock　implementation。　
Here；　I’ll　explain　developing　the　sample　application　by　assembling　individual　pieces　in　a
top…down　manner；　focusing　on　getting　a　single　echo　implemented。　Then　once　the　overall　flow
is　plete；　the　individual　pieces　will　be　implemented　pletely。　Figure　10…2　illustrates
a　plete　architecture　for　the　lottery…prediction　program；　including　the　pipeline　for　the
TextProcessor　console　application。　
Figure　10…2。　Architecture　of　a　reader/writer　application　using　a　general　assembly　
Reading　and　Writing　to　a　Stream　
For　developing　the　lottery…prediction　application；　we’ll　use　a　piece　of　bootstrap　code　to　initiate
the　reading　and　writing　library；　which　then　calls　the　specific　implementation。　Bootstrap　code　is
code　that　does　not　actually　perform　the　processing；　but　is　responsible　for　setting　up　and　initi
ating　another　piece　of　source　code　that　will　do　the　processing。
This　is　the　same　sort　of　architecture　as　we　set　up　in　Chapter　8’s　example；　for　the　applica
tion　to　control　the　lights　of　a　building。　In　that　case；　the　controller　was　a　generic　piece　of　software
that　called　an　interface；　but　did　not　know　about　the　individual　implementations。　The　focus
there　was　on　developing　the　room　implementations；　and　the　lighting　controller　was　left　as　a
nebulous　to…do　task。　Here；　we’ll　go　through　the　creation　of　a　plete　working　application；
including　the　controller　and　implementation。　Note　this　chapter　is　light　on　testing　routines；
both　for　brevity　and　because　one　of　the　exercises　at　the　end　of　the　chapter　is　for　you　to　e　up
with　a　testing　plan。　
We　want　to　be　able　to　process　the　following　mand　line。
type　lotto。txt　｜　TextProcessor。exe　
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254 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　
If　TextProcessor。exe　cannot　read　the　data　from　the　pipe；　an　exception　will　be　thrown　at
the　console　level；　indicating　that　the　piped　data　was　not　read。　
■Note For　the　application　to　work；　the　lotto。txt　and　TextProcessor。exe　files　must　be　in　the　same
directory。　By　default；　TextProcessor。exe　is　in　the ＇Visual　Studio　project＇bindebug　directory。
Copy　TextProcessor。exe　into　the　lotto。txt　directory；　or　vice　versa；　or　you　could　even　copy　them　both
into　another　directory。　
In　the　architecture　of　TextProcessor；　the　bootstrap　code　is　in　the　ReaderWriter　project。
The　TextProcessor　console　application　must　call　the　bootstrap　code　and　instantiate　a　local
type　that　has　implemented　the　IProcessor　interface。　The　Main（）　method　of　TextProcessor　is
implemented　as　follows　（this　is　the　best　time　to　add　a　reference　to　the　ReaderWriter　project　by
right…clicking　TextProcessor　and　choosing　Add　Reference Projects ReaderWriter）：　
Imports　ReaderWriter　
Public　Module　Module1　
Sub　Main（ByVal　args　As　String（））　
Bootstrap。Start（args；　New　LottoTicketProcessor（））　
End　Sub　
End　Module　
TextProcessor。Main（）　passes　all　of　the　given　arguments　（contained　in　the args　array）　to
the　actual　processing　routine　（Bootstrap。Start（））。　The LottoTicketProcessor　class　imple
ments　the　IProcessor　interface　and　will　serve　for　the　temporary　purpose　of　echoing　data。　The
IProcessor　interface　is　defined　in　the ReaderWriter　project　as　follows：　
Public　Interface　IProcessor　
Function　Process（ByVal　input　As　String）　As　String　
End　Interface　
The　IProcessor　interface　has　a　single　method Process（）；　which　accepts　a　string　to　be
processed；　and　the　return　value　is　the　processed　string。　
The　implementation　of LottoLibrary。LottoTicketProcessor　is　as　follows　（remember　to
add　a　referenc