参考文献Word格式.docx
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参考文献Word格式.docx
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ASP.NET
.NETFramework
VisualStudio&
.NET
Summary:
Takeadvantageofinheritanceinthe.NETFrameworktoextendASP.NETclassestomakethemgenerateASP.NETcodethatisfullyaccessibletopeoplewithdisabilities.(13printedpages)
Contents
Introduction
TheWAI,WCAG,andSection508
Microsoft'
sAccessibleASP.NETWebControlsforASP.NET1.x
CreatingAnAdaptive,AccessibleDataGridWebControl
UsingtheAccessibleDataGridColumnClassesinanASP.NETWebPage
AccessibilityinASP.NETWhidbey
RelatedBooks
WhilethemajorityofonlineusersareabletobrowseWebsitesusingWebbrowserswiththetypicalbrowsersettings,userswithdisabilitiescommonlyusealternativemeanstoaccessonlineinformation.Forexample,ablindusermightuseatext-onlybrowserthatconvertsthetextintoBraille,orreadsthetextaloudusingascreenreader.ApersonwithreducedvisionmightstilluseabrowserlikeMicrosoft&
InternetExplorer,butwithascreenmagnifier,orwiththebrowserconfiguredtouseextralargefontsizes.Motordisabilitiesmightprecludeauserfromusingthemouseorkeyboardasaninputdevice.
SincepeoplewithdisabilitiestypicallysurftheWebusingspecialdevicesornon-standardbrowserconfigurations,aWebsite'
soveralldesignandHTMLmarkupgreatlyimpactsthedisabledperson'
suserexperience.Forexample,specifyingfontsizesusingabsolutemeasurements—like10pt—displaysthefontinthatabsolutesize,andnotrelativetothetextsizetheuserhasconfiguredinhisbrowser.SitesthathaveaFlashorShockwaveinterface,anddonotprovideanalternate,textrepresentation,effectivelycutoffuserswithBrailledevicesortext-to-speechsynthesizers.AWebsiteissaidtobeaccessibleifitisdesignedtotransitiongracefullytoalternatedevices.
Atthispoint,youmightbethinking,"
WhyshouldIbotherensuringmyWebsiteisaccessible?
"
TherearetwogoodreasonsIcanthinkof:
1.It'
sGoodBusiness–AccordingtotheU.S.Census2000,49.7millionAmericanshaveadisability;
aJune2000pollbyHarrisInteractiveshowsthat43%ofdisabledAmericansareregularonlineusers,andthatuserswithdisabilitiesspendalmosttwiceasmuchtimeonlinethanuserswithoutdisabilities.Puttheresultsofthesetwosurveystogetherandyou'
llfindthattherearemorethan21millionAmericanswithdisabilitieswhoareregularlyonline.BynottakingthetimetomakeyourWebsiteaccessible,youarecuttingoff21millionpotentialvisitors.
2.
It'
saMandateforGovernmentAgencies–In1998theUnitedStategovernmentpassedSection508oftheRehabilitationAct,requiringFederalagenciestomaketheirelectronicinformationaccessibletoindividualswithdisabilities.ThislawprovidesaccessibilityguidelinesforsoftwareapplicationsandWebapplications,aswellastelecommunicationproductsandvideoproducts.NotonlyareFederalagenciesrequiredtoimplementaccessibilityguidelines,butalsoprivatecompaniesthatarecontractedtoworkfortheFederalgovernment.(AnumberofcountriesoutsidetheU.S.alsohavesimilaraccessibilityrequirementsforgovernmentagencies.)Therefore,creatingaccessibleWebapplicationsisrequiredifyouworkforthegovernmentorforacompanythatprovidesservicestothegovernment.
InthisarticlewewilldiscusswhatstepsyoucantaketoensurethatyourMicrosoft®
ASP.NETWebsiteisaccessible.We'
lltakeabrieflookattheofficialaccessibilityguidelinesavailabletoday,andthenfocusinontheaccessibilityguidelinesusedbytheUnitedStatesgovernment.Thearticlewrapsupwithalookathowtouseinheritancetoturnnon-accessibleASP.NETWebcontrolsintoonesthatmeetaccessibilityguidelines.
ThereareanumberofstepsthatcanbetakentomakeaWebsitemoreaccessible.Butwhat,exactly,arethesesteps,andhowmanyofthemdoesonesiteneedtoemployinordertobeconsideredaccessible?
Theanswerstothesequestionsdifferbasedonwhoyouask,andwhatlevelofaccessibilitytheyneedtoprovide.AnintranetsiteforaFortune500companywouldlikelyrequireahigherdegreeofaccessibilitythananintranetsiteforacompanywithonly25employees.
TheWC3'
sSayonAccessibility
Tohelpformalizethisdiscussion,in1999theWC3officiallyfoundedtheWebAccessibilityInitiative(WAI),agrouptaskedwithimprovingWebsiteusabilityforpeoplewithdisabilities.TheWAI'
sfirstactwastopublishtheWebContentAccessibilityGuidelines,orWCAG.TheWCAGprovidesalistof14guidelinesforaccessibleWebsitedesign.TheguidelinesthemselvesdonotspelloutactionstotaketomakeaWebsitemoreaccessible.Rather,theyarehigh-levelstatementsthatprovidecommentonhowtoensureaccessibility.Forexample,guideline1is"
Provideequivalentalternativestoauditoryandvisualcontent."
Accompanyingeachguidelineisasetofcheckpoints.Thecheckpointsspelloutactionsthatcanbetakentoensurethattheaccessibilityguidelineismet.Eachcheckpointisgivenoneofthefollowingpriorityvalues:
•
Priority1–aWebdevelopermustsatisfythischeckpoint,otherwiseoneormoregroupsofuserswillnotbeabletoaccessthecontent.
Priority2–aWebdevelopershouldsatisfythischeckpoint,otherwiseoneormoregroupsofuserswillfinditdifficulttoaccessthecontent.
Priority3–aWebdevelopermayaddressthischeckpoint,otherwiseoneormoregroupsofusersmighthavedifficultywhenaccessingthecontent.
Inadditiontolistingthe14guidelinesandtheirassociated,prioritizedcheckpoints,theWCAGalsoprovidesathree-levelclassificationscaleforWebsiteaccessibility.SitesthatimplementallPriority1checkpointsareratedatconformancelevelA.ThosethatimplementallPriority1andPriority2checkpointsareratedDouble-A,whilethosethatimplementallofthecheckpointsareratedTriple-A.TheWCAGgivesagoodsetofactionstoperformtoensurevaryinglevelsofaccessibility.
AlthoughathoroughdiscussionoftheWCAGisbeyondthescopeofthisarticle,listedbelowarethe14high-levelguidelinesoftheWCAG.Thecheckpointsforeachguideline,andtheirassociatedpriority,canbefoundattheofficialWebContentAccessibilityGuidelines1.0specification.
15.
Provideequivalentalternativestoauditoryandvisualcontent
16.
Don'
trelyoncoloralone
17.
Usemarkupandstylesheetsanddosoproperly
18.
Clarifynaturallanguageuse
19.
Createtablesthattransformgracefully
20.Ensurethatpagesfeaturingnewtechnologiestransformgracefully
21.Ensureusercontroloftime-sensitivecontentchanges
22.Ensuredirectaccessibilityofembeddeduserinterfaces
23.Designfordevice-independence
24.Useinterimsolutions
25.UseW3Ctechnologiesandguidelines
26.
Providecontextandorientationinformation
27.
Provideclearnavigationmechanisms
28.Ensurethatdocumentsareclearandsimple
sAccessibleASP.NETWebControlsforASP.NET1.x.ManyoftheWCAGcheckpointsandSection508rulesdictatespecificHTMLmarkupthatshouldbeusedtomakeaWebsitemoreaccessible.Forexample,checkpoint5.1intheWCAG(aPriority1checkpoint)andrule(g)inSection508requiresthat<
table>
elementsproperlyidentifyrowandcolumnheaders.Thatis,the<
td>
elementmustbeusedtoidentifydatacells,whereas<
th>
mustbeusedtoidentifyheaders.WhenbuildingASP.NETWebsites,developersrarelyhavetoworryaboutgeneratingHTMLmarkup.Rather,Webcontrolsareusedthatemitthepropermarkup.Unfortunately,manyoftheASP.NETWebcontrolsemitmarkupthatviolatestheaccessibilityrulesoutlinedbytheWCAGandSection508.SinceallWebcontrolsare,fundamentally,classesintheMicrosoft&
.NETFramework,theirfunctionalitycanbeextendedinanumberofwaystoconformtoaccessibilityguidelines.AprimeexampleofenhancinganexistingASP.NETWebcontroltomeetaccessibilityguidelinescanbeseenwiththeDataGridWebcontrol.TheDataGridWebcontrolthatshipswiththe.NETFrameworkdoesnotconformtorule(g)inSection508/checkpoint5.1intheWCAG.Thatis,theheadersarerenderedusing<
elementsinsteadof<
.(ToseewhatImean,checkoutthislivedemo,anddoaView/Sourceinyourbrowser.You'
llseethattheheaderrowuses<
sratherthan<
s.)However,inJune2003MicrosoftreleasedanASP.NETHotfixRollupPackagethat,amongotherthings,includesanimprovedversionoftheDataGrid,onethatconformstorule(g)inSection508.
Note
TheASP.NETHotfixRollupPackageprovidesotheraccessibility-relatedenhancements.Forexample,itaddsanoptionalAssociatedControlIDpropertytotheLabelWebcontroltospecifytheIDoftheWebcontroltheLabelisassociatedwith.Ifthispropertyisprovided,theLabelisrenderedasa<
label>
HTMLelementwiththeforattributereferencingthespecifiedWebcontrol.Formoreinformationconsultthisknowledgebasearticle.
TheWebcontrolsprovidedintheJune2003HotfixbringtheASP.NETWebcontrolsuptoSection508standards.EvenwiththeHotfix,however,therearestillanumberofWCAGPriority1checkpointsnotbeingmet.FortunatelyyoucaneasilyextendthefunctionalityofexistingWebcontrolstoconformtotheaccessibilityguidelinesrequiredbyyourcompany.Thisispossiblethankstothepowerofinheritance.Specifically,wecantakeaWebcontrolthatdoesnotconformtotheaccessibilitystandards,andcreateanextendedWebcontrolthatdoesconformtothestandards.Byusinginheritance,weonlyhavetochan
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