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Hack 21. Let Users Add Custom Items to Predesigned Lists

Hack 21. Let Users Add Custom Items to Predesigned Lists

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Whenauserattemptstoaddanewvaluetothecombobox,

theOnNotInListeventfires.Withinthisevent,acoderoutine

handlesaddingthenewvaluetothelist.



3.4.1.TheCode

Thecodeissimpleandstraightforward.Twoargumentsare

providedtotheroutine:NewDataandResponse.Theeventstub

comespredesignedwiththesearguments,soyoudon'thaveto

createthem:





PrivateSubcmbCustomers_NotInList(NewDataAsString,_

ResponseAsInteger)

DimctlAsControl



Setctl=Me.cmbCustomers



Response=acDataErrAdded



ctl.RowSource=ctl.RowSource&";"&NewData

EndSub



Figure3-11.TheLimitToListpropertysettoYes



TheResponseargumenttellsAccesstooverridethebehaviorof

notallowingavaluetobeadded.Thedeveloperdoesthisby

settingtheResponsetotheadDataErrAddedconstant.Thenewdata

(suppliedbytheNewDataargument)isthenaddedtotheRow

Source.



3.4.2.HackingtheHack

Sofar,thishackworksonthepremisethattheRowSourceTypeis

settoaValueList.IftheRowSourceTypeisTable/Query,youneed

anappendroutinetoplacethenewvalueintheunderlyingdata

store.Inthiscase,theNotInListeventappendsthenewvalue

tothesourcetable.

Hereisanexampleofhowtocodetheroutine.Thisexample

assumesasourcetablenamedtblShippingMethodswithafield

namedShipping-Method:





PrivateSubcmbShippingMethods_NotInList(NewDataAsStr

ResponseAsInteger)



Dimnew_dataAsString

DimconnAsADODB.Connection

Setconn=CurrentProject.Connection

'doubleupanyapostrophesbeforeInsert

new_data=Replace(NewData,"'","''")

Response=acDataErrAdded

conn.Execute"InsertInto"&_

"tblShippingMethods(ShippingMethod)Values('"&_

new_data&"')"

EndSub



Hack22.PopulateandSortListswithFlair



Usethesethreeclevertechniquestopopulateandsort

listboxcontrols.

Listsareintegraltoformdesign.True,notallformsneedalist,

butwhenthey'reapplicable,selectinganitemfromalistis

mucheasierthantypinginthevalue.Thisalsomakesiteasier

toavoidtypos.

Thishackpresentsthreewaystopopulateandsortlistbox

controls.Ineachexample,theunderlyingtablesandstructure

arekeyelements.Theexamplesshowhowtosort

alphabetically,butfromtwosources;howtosortbasedona

keyvalue;howtosortonplacementintheSQLstatement;and

evenhowtosortbytrackingthepopularityofthelistitems

themselves!TheSQLUnionclauseisakeyfactortogetting

muchofthistohappen.



3.5.1.TheForm

Figure3-12showsaformwiththreelists,aptlynamedList1,

List2,andList3.



Figure3-12.Threelistcontrolsonaform



Behindthescenes,twotablespopulatethelistcontrols:

tblFruitsandtblVegetables,showninFigure3-13.Notethat

theysharetwocommonfields:SortNumberandListItem.This

commonstructureisputtogooduse,asyouwillseesoon.



Figure3-13.Twotablesusedtopopulatethelist

controls



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Hack 21. Let Users Add Custom Items to Predesigned Lists

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