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Hack 22. Populate and Sort Lists with Flair

Hack 22. Populate and Sort Lists with Flair

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Behindthescenes,twotablespopulatethelistcontrols:

tblFruitsandtblVegetables,showninFigure3-13.Notethat

theysharetwocommonfields:SortNumberandListItem.This

commonstructureisputtogooduse,asyouwillseesoon.



Figure3-13.Twotablesusedtopopulatethelist

controls



3.5.2.PopulatingaListboxAlphabeticallyfrom

TwoSources

List1displaysthevaluesfromthetwotables,sorted

alphabeticallyasonelargerlist.ThetrickistohavetheList

controlusetherecordsofbothtablesinitsRowSourceproperty.

YoudothisbycombiningtherecordsofbothtablesinaUnion

query.Figure3-14showstheforminDesignmodewiththe

propertysheetsettoList1.



Figure3-14.TheRowSourcepropertyforList1



TheSQLstatementintheRowSourcepropertyreadslikethis:





SelectListItemfromtblFruitsUNIONSelectListItemfr



TheUnionclauseallowsthevaluesfromthetwotablestobe

combined,giventhatthestructureanddatatypearethesame.

Inotherwords,theListItemfieldfromeachtableisaddressed

withtheSQLstatement.Queryingthesamenumberoffieldsin

eachSelectstatementwiththeUnionqueryisarequirement.The

querycan'trunifthenumberoffieldsbeingaccessedfrom

eachtablediffers.

Asaresultthecombinedrecordsaresortedasiftheyreally

comefromonesource(whichtechnicallyistrueviatheUnion

query).Therefore,thedistinctionoffruitsandvegetablesis

purposelylost,andinstead,asparagusfollowsapple,broccoli

followsbanana,andsoon.

Thistechniqueisusefulwhenyouneedtopresentitemsinalist

thatcomefrommorethanonesource.Asdiscussedinthe

followingsection,youcanbringtogetherasmanysourcesas

youneedwithmultipleUnionclauses.



3.5.3.ControllingtheSortinaListboxPopulated

fromMultipleSources

InFigure3-12,List2showstheresultofsortingfruitsina

certainorderandvegetablesinacertainorder.Additionally,the

fruitsandvegetablesaren'tsortedwitheachother.Thelistalso

includesseparatorsandvaluesnotfoundinthesourcetables:

All,AllFruits,andAllVegetables.Howdidalltheseitemsget

intothelist?

AUnionquerypopulatesthelistbox.ThetwosourcestblFruits

andtblVegetablesareused,butinsteadoflettingthelistmix

andsorttheitemsalphabetically,theSortNumberfieldcontrols

thesort.



AkeypointhereisthattherangeofvaluesforSortNumberin

thetblFruitstableisdifferentfromtherangeofvaluesfor

SortNumberinthetblVegetablestable.TheUnionoperation

actuallydoescombinebothsourcesintoonesort,butthe

SortNumberfieldrangeskeepthetwolistsapartinthelistbox.

Figure3-15showstheforminDesignmodewiththeproperty

sheetsettoList2.TheSQLstatementthatservesastheRow

SourcepropertyisdisplayedintheZoombox.

HereistheSQLstatement:



Select"All"asa,-2asSortNumberfromtblFruits

UnionSelect"---"asa,-1asSortNumberfromtblFruits

UnionSelect"AllFruits"asa,0asSortNumberfromtblFru

UnionSelectListItem,SortNumberFromtblFruits

UnionSelect"---"asa,99asSortNumberfromtblVegetable

UnionSelect"AllVegetables"asa,

100asSortNumberfromtblVegetables

UnionSelectListItem,SortNumberFromtblVegetables

OrderBySortNumber



Figure3-15.TheRowSourcepropertyforList2



Quiteabitisgoingonhere.Overall,theSQLcombinesitems

fromthesourcetableswithitemsprovidedrightwithintheSQL.

AllthesetietogetherviatheSortNumberfield.

ThisSQLstatementusestheUnionclauseseveraltimes,tomake

surethatallSelectstatementspointtothesamenumberof

fields.Inthisexample,thatnumberis2.

TheSQLstartsbygettingthewordAlltothetopofthelist.

ThissnippetforcesthewordAllintothelist:

Select"All"asa,-2asSortNumber



ThecodesnippetdoesthisbygivingthewordAllthelowest

valueofSortNumberinthiscase,-2.Tobeclear,neithertheword

Allnorthevalue-2actuallycomesfromanunderlyingtable.

However,theirplacementintheSQLfollowsthestructureofall

theotherSelectstatementsintheSQL,whichallowsthemtobe



combinedwiththeothervaluesbeingaccessedbytheSQL.

TheSQLusesUniontocombinevaluesfromthetableswith

theseon-the-flyvalues.Anumberofthesevaluesareinthe

SQL:



Select"All"asa,-2asSortNumberfromtblFruits

Select"---"asa,-1asSortNumberfromtblFruits

Select"AllFruits"asa,0asSortNumberfromtblFruits

Select"---"asa,99asSortNumberfromtblVegetables

Select"AllVegetables"asa,100asSortNumberfromtblVeg



AllthesepartsoftheSQLforcethelisttopresentavalue:All,

AllFruits,AllVegetables,or---.Noneofthesevaluescomes

fromthetables.However,allofthemarepairedwithasort

number,andthisiswhatplacesthemintheirsequentialplace

inthelistbox.

Considerthesortnumbersassociatedwiththeseon-the-fly

items,whileconsideringthesortnumbersoftheitemsinthe

tables(seeFigure3-13).Sortnumbersforthevegetablesstart

at101.Therefore,theAllVegetablesitemhasbeenassociated

withthenumber100.Thisforcesittoappearinthelistdirectly

abovetheactualvegetables.

Keepinmindthatalistboxsuchasthis,withseveralpossible

itemsausercanselect,alsorequiresarelatedlevelof

functionalitytohandletheuser'sselection.Ifauserselectsa

singlefruitorvegetable,chancesaretheapplicationwill

continueprocessing.However,whatifauserselectsAllFruits?

YourprocessingwillneedtohandleallthevaluesinthetblFruits

table.

Alsonotethatyouentertheseparatorcharacters(---)intothe

listforthesakeofsegregatingpartsofthelengthylistofitems.

Thisisratherpleasingforsomeonescrollingthroughalonglist;



however,ausercanselecttheseparators!Therefore,youneed

toensurethatuservalidationandfeedbackareinplaceincase

thishappens.Typically,ifauserselectstheseparator

characters,amessageshouldappearalertinghimtomake

anotherselection.



3.5.4.SortingListItemsbyPopularity

It'snotalwayseasytoknowaheadoftimewhichitemsusers

willselectmostoftenfromalist.YoucanuseaSortNumber

fieldtoarrangelistitemsinawaythatseemsbest,butthereis

anevenbetterwaytodothis.

Whynotletuseractionsdrivethewaythelistissorted?

Keepinginmindthatitiseasytosortalistbyanumericalfield,

logicdictatesthatthevaluesinthenumericalfieldshould

reflectthepopularityofthelistitems.

Thisiseasytodobyupdatingalist'sSortfieldeachtimeitis

selected.Figure3-16showstheforminDesignmodewiththe

propertysheetsettoList3.

Here'stheRowSourceSQLstatementforList3:



SELECTOccurrence,ListItemFROMtblFruitsORDERBYOccurr



ThislistboxusesthetblFruitstableexclusively.Thistablehas

theadditionalOccurrencefield,whichdrivesthewayitemsare

sortedinthelistbox.NotefromtheRowSourcepropertythat

itemsarelistedbasedontheOccurrencefieldvaluesbeingin

descendingorder.



Figure3-16.TheRowSourcepropertyforList3



Tomakesenseofthis,itisnecessarytosomehowupdatethe

valuesintheOccurrencefield.Thisupdateoccurswhenyou

processtheselectedlistvalueinwhateverwayyourprocessing

works.Forthepurposeofthisdemonstration,abuttonhas

beenplacedontheform.Here'stheClickeventforthebutton:





PrivateSubcmdUpdateCount_Click()

'getthecurrentcountforthisitem



Dimselected_item_countAsInteger



IfNotIsNull(Me.List3)Then

selected_item_count=_

DLookup("Occurrence","tblFruits","ListItem='"&Me





'increasethecountandupdatethetable





selected_item_count=selected_item_count+1





DoCmd.SetWarningsFalse





DoCmd.RunSQL("UpdatetblFruitsSetOccurrence=





selected_item_count&"WhereListItem='"&





Me.List3.Requery



EndIf







EndSub



Inanutshell,theDLookupfunctionfindsthecurrentvalueofthe

Occurrencefieldfortheselecteditemandstoresitinthe

selected_item_countvariable.Thevalueisincrementedby1,anda

SQLUpdatestatementwritesthevaluebackintothetable,for

thegivenitem.Finally,thelistisrefreshedsothatontheform

thelistwillresort.

Asaresult,whenitemsinthelistareselectedandprocessed,

theyfloattothetopofthelist.Youcanseethisbycomparing

theplacementofitemsinList3inFigure3-12withthevalues

oftheOccurrencefieldinthetblFruitstableinFigure3-13.For

example,raspberryisthefirstiteminList3becauseithasthe

highestvalueintheOccurrencefield.



Hack23.UseCustomControlsonYourForms



MovepaststandardAccesscontrols,anddiscovernew

designpossibilities.

IfyoudevelopenoughAccessapplications,youbegintotake

theToolboxforgranted.Youknowallthecontrolsandwhento

usethem.ButdidyouevernoticetheToolboxhasabuttonthat

leadstomorecontrols?Figure3-17showswherethisbuttonis

located.



Figure3-17.Findingadditionalcontrols



ClickingtheMoreControlsbuttonopensalistofnewcontrols

fromwhichtoselect.Idon'tsuggesttestingallofthembecause

Ithinkthatsomearen'tusefulinAccess.However,ifyouscroll

totheMicrosoftcontrols,youmightfindsomeinterestingones

totryonaform.Let'sseehowwecanuseafewofthese

customcontrols.



3.6.1.AddingaCustomControltoaForm

Thelistofcontrolswillprobablydifferbetweencomputer

systems,butit'sasafebetthatyouhavetheMicrosoftForms

controlsloadedonyourcomputerbecausetheyareinstalled

withMicrosoftOffice.

Asanexample,IplacedaMicrosoftForms2.0spinbutton

controlonaform,asshowninFigure3-18.Ididthisbysimply

selectingitfromthelongcontrollistandthendrawingonthe

formusingthemouse.



Figure3-18.Aspinbuttoncontrolonaform



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