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Displaying and Searching PDF Content.docx

文档编号：11235936
上传时间：2023-02-26
格式：DOCX
页数：9
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Displaying and Searching PDF Content.docx

DisplayingandSearchingPDFContent

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DisplayingandSearchingPDFContentoniPhone

PDFparsingisablackartthatmostprogrammersavoid.“Madnesslurkshere.”Theymumbletothemselvesquietly.ChoosinginsteadtopushtheirPDFsthroughUIWebViewsandcommitothercrimesagainsthumanity.

Itdoesn’thavetobethisway,however.Parsing,displaying,andsearchingPDFsnativelyandatalowlevelisactuallysurprisinglyeasyifyou’renotafraidtogetyourhandsalittledirtywiththeCoreGraphicsPDFfunctions.I’mgoingtoshowyouhow.

Where’sithiding?

Thefirstthingtoknowisthatinordertodothis,youneedtouseCoreGraphicscalls.SoyouneedtoincludetheCoreGraphicsframeworkinyourproject,andinanyfilesyouwanttousethecalls,youhavetoincludetheCoreGraphics.hheader.It’sprobablyalsoworthwhiletoreviewtheCoreFoundationmemorymanagementrules.

Onceyou’vedonethis,it’sverystraightforwardtoreadyourPDFfilesanddisplaytheminacustomview.Let’stakealookathowwedothat.

InitializingaPDFDocument

ToinitializeaPDFdocument,youfirsthavetousethecallCGPDFDocumentCreate,passingintheURLtothedocumentyouwanttoopen.SinceNSURListollfreebridgedtoCFURLRef,youcancreateaCFURLRefjustusingplainoldNSURLlikeso:

NSString*pathToPdfDoc=[[NSBundlemainBundle]

pathForResource:

@"mypdf"ofType:

@"pdf"];

NSURL*pdfUrl=[NSURLfileURLWithPath:

pathToPdfDoc];

Then,tocreatetheCGPDFDocumentRef,callCGPDFDocumentCreateWithURL:

CGPDFDocumentRefdocument=CGPDFDocumentCreateWithURL（（CFURLRef）pdfUrl）;

DisplayingPages

Sonowyouhaveadocument.Todisplaythecontentofthedocument,youhavetogetthecontentintheformofpages.PDFsarealreadyformattedbypages,soallyouneedtodoisgetatthatdata.FortunatelyCoreGraphicshasfunctionsforthattoo.

Togetthetotalcountofthepagesinthedocument,youusethecallCGPDFDocumentGetNumberOfPages,whichtakesasaparameter,thedocumentyoucreatedabove.So,forexample:

size_tpageCount=CGPDFDocumentGetNumberOfPages（document）;

Then,togetanindividualpagetodisplayinyourview,youusethefunctionCGPDFDocumentGetPage,passingthedocumentandthepagenumberyouwant.Likeso:

CGPDFPageRefpage=CGPDFDocumentGetPage（document,currentPage）;

NotethatthecurrentPageparameterhereis1based,not0basedasistheusualcaseinprogramming.ThismeansthatthefirstpageofthePDFdocumentisinfact,page1,andnotpage0.

Onceyouhavethepage,youcandisplayitinyourcustomview.TheonlycomplicatedparthereisthatoniPhone,thecoordinatesystemisflippedcomparedtotheMac.ThiscausesaproblembecausetheCoreGraphicsPDFsystemusesthedesktopcoordinatesystemevenoniPhone.（It’syucky,Iknow.）Thesolutiontothisistoflipthepage（thiscanbedoneinyourdrawRectmethodwhenyougotodrawthecontent）:

CGPDFPageRefpage=CGPDFDocumentGetPage（document,currentPage）;

CGContextRefctx=UIGraphicsGetCurrentContext（）;

CGContextSaveGState（ctx）;

CGContextTranslateCTM（ctx,0.0,[selfbounds].size.height）;

CGContextScaleCTM（ctx,1.0,-1.0）;

CGContextConcatCTM（ctx,

CGPDFPageGetDrawingTransform（page,kCGPDFCropBox,[selfbounds],0,true））;

ThekeyhereisthecalltoCGContextScaleCTM.Whatwedo,iswegetthecurrentdrawingcontext,andthenwescaleit’scoordinatesystemonit’syaxisby-1.0.This,effectively,flipsitupsidedownalongit’shorizontal（x）axis.

Finally,wedrawthepageintothecontextusingtheCGContextDrawPDFPagefunction:

CGContextDrawPDFPage（ctx,page）;

CGContextRestoreGState（ctx）;

p.

Sobasically,afullon@drawRect@methodforacustomviewthatdrawscontentfromaPDFpage,lookssomethinglikethis:

bc..-（void）drawRect:

（CGRect）inRect;

{

if（document）

{

CGPDFPageRefpage=CGPDFDocumentGetPage（document,currentPage）;

CGContextRefctx=UIGraphicsGetCurrentContext（）;

CGContextSaveGState（ctx）;

CGContextTranslateCTM（ctx,0.0,[selfbounds].size.height）;

CGContextScaleCTM（ctx,1.0,-1.0）;

CGContextConcatCTM（ctx,

CGPDFPageGetDrawingTransform（page,kCGPDFCropBox,

[selfbounds],0,true））;

CGContextDrawPDFPage（ctx,page）;

CGContextRestoreGState（ctx）;

}

p.

That'sallthereistoit!

SearchingPDFs

OneofthethingsthatseemstobeparticularlyscarytoprogrammersissearchingPDFs.Iagreethatit’scertainlynotpleasantstufftocode,butit’snothardeither.

Now,IwanttoprefacethisbysayingthatIfeelthiscodeisabitofahack,butitdefinitelyworks,andseemstoworkquitewell.Perhapsthere’sabetterwaytodothis,andifyouknowofone,pleaseletmeknow.Thatsaid,however,here’showI’vedoneit.

ThefirstthingtoknowisthatPDFfilesaremadeupofoperatorswhichdelineatethedatawithinthem.So,forexample,alltextinaPDFdocumentisstoredasglyphsandprefixedbyoperatorsoftypeeither“Tj”,inthecaseofastring,or“TJ”inthecaseofanarrayofstrings.Knowingthis,youcanaccessthePDFdataasastreamandcreateascannerwhichwillcallcallbackmethodsyouspecifywhentheseoperatorsareencountered.Youcanthenretrievethedataaftertheoperatoranduseittobuildyoursearchcorpus.

Thatprobablysoundsintimidating,butit’tnot.Youstartoutbycreatingaclassthatwillbeyour“pagesearcher.”Thiswillholdthestateforyoursearchengine.Here’sthelistingfortheinterfaceforthisclass:

#import

@interfacePDFSearcher:

NSObject

{

CGPDFOperatorTableReftable;

NSMutableString*currentData;

}

@property（nonatomic,retain）NSMutableString*currentData;

-（id）init;

-（BOOL）page:

（CGPDFPageRef）inPagecontainsString:

（NSString*）inSearchString;

@end

p.

Prettystraightforwardstuff.WeusethecurrentDatamembertostorethetextofthepagebeingscanned.Thisisamembervariableratherthanalocalvariablebecausewe'regoingtobeusingCfunctionstofillitin.Don'tworry,that'llmakesenseinamoment.

The@init@methodfortheclassactuallycreatesthecallbacktable:

bc..-（id）init

{

if（self=[superinit]）

{

table=CGPDFOperatorTableCreate（）;

CGPDFOperatorTableSetCallback（table,"TJ",arrayCallback）;

CGPDFOperatorTableSetCallback（table,"Tj",stringCallback）;

}

returnself;

}

ThearrayCallbackandthestringCallbackfunctionsareCfunctionsthatwillbecalledbythescanner.They’reshownhere:

voidarrayCallback（CGPDFScannerRefinScanner,void*userInfo）

{

PDFSearcher*searcher=（PDFSearcher*）userInfo;

CGPDFArrayRefarray;

boolsuccess=CGPDFScannerPopArray（inScanner,&array）;

for（size_tn=0;n

{

if（n>=CGPDFArrayGetCount（array））

continue;

CGPDFStringRefstring;

success=CGPDFArrayGetString（array,n,&string）;

if（success）

{

NSString*data=（NSString*）CGPDFStringCopyTextString（string）;

[searcher.currentDataappendFormat:

@"%@",data];

[datarelease];

}

voidstringCallback（CGPDFScannerRefinScanner,void*userInfo）

{

PDFSearcher*searcher=（PDFSearcher*）userInfo;

CGPDFStringRefstring;

boolsuccess=CGPDFScannerPopString（inScanner,&string）;

if（success）

{

NSString*data=（NSString*）CGPDFStringCopyTextString（string）;

[searcher.currentDataappendFormat:

@"%@",data];

[datarelease];

}

p.

Asyoucansee,thesewillbecalledwhentheoperatorsfire.Whentheydo,wepopthedataoffthescanner,andaddittothesearcher'scorpus.Theuserinfopointerisactuallypointingtooursearcherobject（basedonthefactthatwewillpassitasthesecondparameterto@CGPDFScannerCreate@inthenextcode）.SowecantypecastittoaPDFSearcherandthenaccessthatcurrentDatamember（rememberIsaiditwouldmakesenselater?

）.

Theactualsearchmethodlookslikethis:

bc..-（BOOL）page:

（CGPDFPageRef）inPagecontainsString:

（NSString*）inSearchString;

{

[selfsetCurrentData:

[NSMutableStringstring]];

CGPDFContentStreamRefcontentStream=CGPDFContentStreamCreateWithPage（inPage）;

CGPDFScannerRefscanner=CGPDFScannerCreate（contentStream,table,self）;

boolret=CGPDFScannerScan（scanner）;

CGPDFScannerRelease（scanner）;

CGPDFContentStreamRelease（contentStream）;

return（[[currentDatauppercaseString]

rangeOfString:

[inSearchStringuppercaseString]].location!

=NSNotFound）;

}

p.

Basically,wecreateastreamfromthepagedata,thenusethatandourcallbacktabletocreateascanner.Wethenscanthedata.It'satthispointourcurrentDatamemberisbeingfilledwiththedatafromthePDFasstrings.Finally,wejustsearchthatstringforoursearchstring.

Easypeezy.

Note:

muchofthiscodeisonlysightcompiled.IpulleditfromsomecodeIhad,butitwasn'tastraightacrosscopy,soifyoufindanerror,pleaseletmeknow.