《VB2008从入门到精通(PDF格式英文版)》第139章

The　workbook　and　worksheet　could　be　defined　as　interfaces　or　as　classes。　Which　would　be
better？　Let’s　assume　that　workbook　will　be　defined　as　an　interface　and　then　implemented　by　a
class。　The　approach　is　a　mitment　to　a　ponent　architecture；　allowing　you　to　implement
multiple　types　of　workbooks。　However；　the　likelihood　of　implementing　multiple　workbook
types　is　rather　remote；　so　why　use　interfaces？　Because　interfaces　fit　better　into　a　bigger　context。　
Let’s　say　that　you　have　pleted　your　super…duper　server…side　application　and　want
to　programmatically　share　the　code　with　multiple　machines。　Having　one　puter　call
functionality　on　another　machine　is　almost　trivial；　but　to　attain　the　best　performance　and
resource　usage；　you　should　use　interfaces。　
Defining　the　Server　Spreadsheet　Interfaces　
Defining　the　interfaces　for　the　server　spreadsheets　is　actually　rather　plicated　because　of
the　requirements。　The　requirements　state　performance　and　usability　are　important；　which；　in
this　case；　is　asking　quite　a　bit；　as　you　will　see　as　we　work　through　the　example。　Let’s　start　with　a
bottom…up　development　approach　and　outline　the　interfaces。　
Defining　the　Debug　Interface　
Because　the　spreadsheet　is　from　a　production　coding　example；　included　in　the　discussion　will
be　pieces　of　code　that　demonstrate　good　programming　practices。　The　following　is　the　base
interface　for　all　of　my　interfaces；　which　is　defined　in　the　Devspace。Trader。mon　project。　
Public　Interface　IDebug
Property　Debug（）　As　Boolean　
End　Interface　
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CH　AP　T　E　R 1　1 ■ L　E　A　R　N　IN　G AB　O　U　T 。　N　E　T G　E　N　E　R　I　CS　293　
The　IDebug　interface　has　a　single　Boolean　property　called　Debug；　which　can　be　assigned　and
retrieved。　The　idea　behind　the　IDebug　interface　is　to　enable　a　ponent　to　generate　debug
output。　One　of　the　major　headaches　with　debugging　applications　that　process　large　amounts
of　data　is　finding　where　the　problem　is。　Imagine　processing　several　million　records；　and　the
bug　happens　in　record　900；001。　You　don’t　want　to　debug　900；000　records　before　hitting　the　bug。
Thus；　the　challenge　is　figuring　out　what　went　wrong　without　using　the　debugger。　This　is　where
IDebug　es　into　play。　It　provides　a　mechanism　to　let　the　implementation　say　what　is　going
on；　so　if　a　bug　needs　to　be　deciphered；　you　do　so　by　looking　at　the　output。　
The　following　example　demonstrates　how　to　use　the　Debug　flag。　The　class　that　contains　this
code　implements　the　IDebug　interface　and　sets　the　Debug　flag　at　the　beginning　of　its　execution。　
Dim　baseType　As　String（）　=　_　
typeToInstantiate。Split（New　String（）　｛　〃＇＇〃；　〃＇＇〃　｝；　StringSplitOptions。None）　
If　baseType。Length　=　0　Then　
Throw　New　Exception（〃There　is　no　base　type；　which　is　an　error〃）　
End　If　
If　Debug　Then　
For　Each　str　As　String　In　baseType
GenerateOutput。Write（〃Workbook。Load〃；　〃baseType（〃　&　str　&　〃）〃）　
Next　
End　If　
The　first　line　of　code　is　used　to　split　up　a　buffer　into　individual　pieces；　where　double　square
brackets　delimit　the　buffers。　The　Debug　property　is　used　to　output　the　split…up　buffer　using　the
mand　GenerateOutput。Write（）。
■Tip Although　I　have　defined　my　own　debugging　infrastructure；　there　is　another　infrastructure　that　you　can
use；　called　log4net　（http：//logging。apache。org/log4net/）。　This　is　a　prehensive　infrastructure
that　you　may　want　to　investigate。　
A　Debug　flag　was　used　to　output　some　text；　otherwise；　that　information　is　not　usually　visible。
Without　a　Debug　flag；　the　only　way　to　get　that　information　is　by　setting　a　breakpoint　after　the
Split（）　statement；　and　then　individually　investigating　the　resulting　buffers。　If　you　had　to　do
that　for　900；000　records；　you　would　bee　bored　very　quickly；　and　let’s　not　even　talk　about
how　much　time　you　would　waste。　
The　Debug　flag　serves　two　purposes。　The　first　is　to　generate　output　to　allow　you　to　do　a　post
mortem　analysis　when　trying　to　figure　out　a　bug。　The　second　is　to　generate　output　when　a　bug
occurs　in　a　production　context。　By　giving　the　user　the　ability　to　define　a　Debug　flag；　you　are　no
longer　reliant　on　having　the　user　explain　to　you　step　by　step　how　to　reproduce　the　bug。　All　you
need　to　do　is　tell　the　user　to　activate　the　Debug　flag　（your　program　would　probably　have　a　menu
item　for　this）；　run　the　program　until　the　bug　occurs；　and　then　send　you　the　debug　log　file　output
for　analysis。　
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Defining　the　IWorksheetBase　and　IWorksheet　Interfaces　
The　worksheet　is　implemented　using　worksheet　and　workbook　interfaces。　Remember　that　one
of　the　requirements　is　to　have　a　spreadsheet　implementation　that　is　very　fast。　This　would　mean
if　a　spreadsheet　contained　numbers；　the　best　implementation　would　be　a　spreadsheet　of
Double　types。　However；　if　the　spreadsheet　contained　string　buffers；　the　best　implementation
would　be　a　spreadsheet　of String　types。　Figure　11…2　shows　a　spreadsheet　of　Double　and
String　types。　
Figure　11…2。　Spreadsheet　of　strings　and　doubles　
In　Figure　11…2；　the　workbook　references　a　worksheet　of　type　Worksheet（Of　Double）　and
Worksheet（Of　String）；　and　in　the　general　case；　Worksheet（Of　BaseType）。　You　can　see　how　an
interface　using generics　for　a　worksheet　could　be　potentially　defined：　define　a　general
worksheet　and　define　the　actual　type　using generics。　The　problem　with　th