Note that xmlpullparser. nexttext () of Android ()

Source: Internet
Author: User

 

Watch out for xmlpullparser. nexttext () posted by Tim Bray on 19 December 2011 at 10: 55 am

[This post is by Jesse Wilson from the Dalvik team.-Tim Bray]

Using
Xmlpullparser is an efficient and maintainable way to parse XML on Android. Historically android has had two implementations of this interface:

  • Kxmlparser,
    Xmlpullparserfactory. newpullparser ().

  • Expatpullparser,
    XML. newpullparser ().

The implementation fromXml.newPullParser()Had a bug where calltonextText()Didn't always advance to
END_TAGAs the documentation promised it wocould. As a consequence, some apps may be working around the bug with extra calltonext()Or
nextTag():

    public void parseXml(Reader reader)            throws XmlPullParserException, IOException {        XmlPullParser parser = Xml.newPullParser();        parser.setInput(reader);        parser.nextTag();        parser.require(XmlPullParser.START_TAG, null, "menu");        while (parser.nextTag() == XmlPullParser.START_TAG) {            parser.require(XmlPullParser.START_TAG, null, "item");            String itemText = parser.nextText();            parser.nextTag(); // this call shouldn’t be necessary!            parser.require(XmlPullParser.END_TAG, null, "item");            System.out.println("menu option: " + itemText);        }        parser.require(XmlPullParser.END_TAG, null, "menu");    }    public static void main(String[] args) throws Exception {        new Menu().parseXml(new StringReader("<?xml version='1.0'?>"                + "<menu>"                + "  <item>Waffles</item>"                + "  <item>Coffee</item>"                + "</menu>"));    }

In ice cream sandwich we changedXml.newPullParser()To return a kxmlparser and deleted our expatpullparser class. This fixesnextTag()Bug. Unfortunately, apps that currently work around the bug may crash under ice cream sandwich:

org.xmlpull.v1.XmlPullParserException: expected: END_TAG {null}item (position:START_TAG <item>@1:37 in java.io.StringReader@40442fa8)      at org.kxml2.io.KXmlParser.require(KXmlParser.java:2046)     at com.publicobject.waffles.Menu.parseXml(Menu.java:25) at com.publicobject.waffles.Menu.main(Menu.java:32)

The fix is to callnextTag()After a callnextText()Only if the current position is notEND_TAG:

  while (parser.nextTag() == XmlPullParser.START_TAG) {      parser.require(XmlPullParser.START_TAG, null, "item");      String itemText = parser.nextText();      if (parser.getEventType() != XmlPullParser.END_TAG) {          parser.nextTag();      }      parser.require(XmlPullParser.END_TAG, null, "item");      System.out.println("menu option: " + itemText);  }

The code above will parse XML correctly on all releases. If your application usesnextText()Extensively, use this helper method in place of callto
nextText():

  private String safeNextText(XmlPullParser parser)          throws XmlPullParserException, IOException {      String result = parser.nextText();      if (parser.getEventType() != XmlPullParser.END_TAG) {          parser.nextTag();      }      return result;  }

Moving to a single xmlpullparser simplifies maintenance and allows us to spend more energy on improving system performance.

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