Lap Trinh Tren Android 3 4762 Diendandaihoc.vn 04505303112011

8/3/2019 Lap Trinh Tren Android 3 4762 Diendandaihoc.vn 04505303112011

1/6

V d 6. Trnh x l SAX

import staticorg.developerworks.android.BaseFeedParser.*;

public class RssHandler extends DefaultHandler{private List messages;private Message currentMessage;private StringBuilder builder;

public List getMessages(){return this.messages;

}

@Overridepublic void characters(char[] ch, int start, int

length)throws SAXException {

super.characters(ch, start, length);

builder.append(ch, start, length);}

@Overridepublic void endElement(String uri, String

localName, String name)throws SAXException {

super.endElement(uri, localName, name);if (this.currentMessage != null){

if (localName.equalsIgnoreCase(TITLE)){

currentMessage.setTitle(builder.toString());} else if

(localName.equalsIgnoreCase(LINK)){

currentMessage.setLink(builder.toString());} else if


2/6

(localName.equalsIgnoreCase(DESCRIPTION)){

currentMessage.setDescription(builder.toString());} else if

(localName.equalsIgnoreCase(PUB_DATE)){

currentMessage.setDate(builder.toString());} else if

(localName.equalsIgnoreCase(ITEM)){messages.add(currentMessage);

}builder.setLength(0);

}}

@Override

public void startDocument() throws SAXException {super.startDocument();messages = new ArrayList();builder = new StringBuilder();

}

@Overridepublic void startElement(String uri, String

localName, String name,Attributes attributes) throws SAXException

{super.startElement(uri, localName, name,

attributes);if (localName.equalsIgnoreCase(ITEM)){

this.currentMessage = new Message();}

}}

Lp RssHandler m rng lporg.xml.sax.helpers.DefaultHandler. Lp ny cung cp cc thc thimc nh, khng thao tc cho tt c cc phng thc tng t cc s kin c tora bi trnh phn tch SAX. iu ny cho php cc lp con ch ghi chn ln cc


3/6

phng thc khi cn thit. RssHandlerc mt API b sung, getMessages.Ci ny tr v danh sch cc i tng Messagem trnh x l thu thp c khin nhn cc s kin t trnh phn tch SAX. N c hai bin trong khc, mt lcurrentMessagecho th hin Messageang c phn tch, v mt l bin

StringBuildergi l builderlu tr d liu k t t cc nt vn bn. Ccbin ny u c bt u khi phng thc startDocumentc dn ra khitrnh phn tch gi s kin tng ng cho trnh x l.

Hy xem phng thc startElement trong V d 6. Phng thc ny c gimi khi bt gp th m trong ti liu XML. Bn ch cn quan tm khi no th lth ITEM. Trong trng hp , bn to ra mt Messagemi. By gi hy nhnvo phng thc characters. Phng thc ny c gi ra khi bt gp d liuk t t cc nt vn bn. D liu d dng c thm vo bin builder. Cui

cng hy xem phng thc endElement. Phng thc ny c gi ra khi btgp th kt thc. i vi cc th tng ng vi cc c tnh ca mt Message,ging nh TITLE v LINK, c tnh thch hp c thit t trncurrentMessages dng d liu t bin builder. Nu th kt thc l mtITEM, th currentMessagethm vo danh sch Messages. y l s phn tchSAX rt in hnh; y khng c g l duy nht i vi Android. V th nu bn

bit cch vit mt trnh phn tch SAX Java, th bn bit cch vit mt trnh phntch SAX Android. Tuy nhin, Android SDK c b sung thm mt s tnh nngthun tin vo SAX.

Phn tch SAX d dng hn

Android SDK c cha mt lp tin ch c gi l android.util.Xml. V d7trnh by cch ci t mt trnh phn tch SAX vi cng lp tin ch nh th.

V d 7. Trnh phn tch SAX Android

public class AndroidSaxFeedParser extendsBaseFeedParser {

public AndroidSaxFeedParser(String feedUrl) {super(feedUrl);

}


4/6

public List parse() {

RssHandler handler = new RssHandler();try {

Xml.parse(this.getInputStream(),Xml.Encoding.UTF_8, handler);

} catch (Exception e) {throw new RuntimeException(e);

}return handler.getMessages();

}

}

Lu l lp ny vn s dng trnh x l SAX chun, v n gin bn s dngli RssHandlernh trong V d 7 trn. Vic c th s dng li trnh x lSAX rt tt, nhng n vn c i cht phc tp v m trnh. Bn c tng tng,nu bn phi phn tch mt ti liu XML phc tp hn rt nhiu, trnh phn tch cth tr thnh mnh t mu m cho cc li. V d, hy xem li phng thcendElement trong V d 6. Lu cch phng thc ny kim tra nh th nonu currentMessagec gi tr khng trc khi n c ci t cc thuc tnh?By gi hy nhn vo XML mu trong V d 4. Lu rng c cc th TITLEv

LINKnm ngoi cc th

ITEM. l l do ti sao kim tra gi tr khng ca

vo. Nu khng th th TITLE u tin c th gy ra mtNullPointerException. Android bao gm c bin th SAX API ca chnhn (xem V d 8) loi b yu cu bn phi vit trnh x l SAX ca chnh bn.

V d 8. Trnh phn tch SAX Android n gin

public class AndroidSaxFeedParser extendsBaseFeedParser {

public AndroidSaxFeedParser(String feedUrl) {super(feedUrl);

}

public List parse() {final Message currentMessage = new Message();


5/6

RootElement root = new RootElement("rss");final List messages = new

ArrayList();Element channel = root.getChild("channel");

Element item = channel.getChild(ITEM);item.setEndElementListener(new

EndElementListener(){public void end() {

messages.add(currentMessage.copy());}

});

item.getChild(TITLE).setEndTextElementListener(newEndTextElementListener(){

public void end(String body) {currentMessage.setTitle(body);

}});

item.getChild(LINK).setEndTextElementListener(newEndTextElementListener(){

public void end(String body) {

currentMessage.setLink(body);}

});

item.getChild(DESCRIPTION).setEndTextElementListener(new

EndTextElementListener(){public void end(String body) {

currentMessage.setDescription(body);}

});

item.getChild(PUB_DATE).setEndTextElementListener(new

EndTextElementListener(){public void end(String body) {

currentMessage.setDate(body);}

});


6/6

try {Xml.parse(this.getInputStream(),

Xml.Encoding.UTF_8,root.getContentHandler());

} catch (Exception e) {throw new RuntimeException(e);

}return messages;

}}

Nh ha, m phn tch SAX mi khng s dng trnh x l SAX. Thay vo n s dng cc lp t gi android.sax trong SDK. Cc lp ny cho php bn m

hnh ha cu trc ca ti liu XML ca bn v thm mt trnh nghe s kin nucn. Trong m trnh trn,bn khai bo rng ti liu ca bn s c mt phn t gcc tn rssv rng phn t ny s c ba phn t con l channel. Tip n bnni rng channels c ba phn t con c gi l ITEMv bn bt u gn cctrnh nghe. i vi mi trnh nghe, bn s dng mt lp bn trong v danh thc hin giao din bn quan tm (hoc EndElementListner hocEndTextElementListener). Ch khng cn phi theo di d liu k t.Vic ny khng ch n gin hn m thc s cn hiu qu hn. Cui cng, khi bngi dnphng thc tin ch Xml.parse, by gi bn a vo trnh x l c tora t phn t gc.

Ton b m trnh trn trong V d 8thuc loi ty chn. Nu bn thy thoi mivi m trnh phn tch SAX chun trong mi trng Java, th bn c th tch vo. Nu bn mun th cc trnh bao bc tin li do Android SDK cung cp, bncng c th s dng n. Nu bn khng mun s dng SAX th sao y? Vn cnc mt vi la chon khc. La chn u tin bn s thy l DOM.

Documents

Lap Trinh Tren Android 3 4762 Diendandaihoc.vn 04505303112011