在下面的程序中，我不了解NodeList的流程和使用。为什么在这里使用NodeList以及它在程序中使用的目的是什么？如果它很重要，请帮助我从NodeList的行中了解它。
package net.learn2develop.Networking;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class MainActivity extends Activity {
ImageView img;
private class BackgroundTask extends AsyncTask<String, Void, Bitmap> {
protected Bitmap doInBackground(String... url) {
//---download an image---
Bitmap bitmap = DownloadImage(url[0]);
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return bitmap;
}
protected void onPostExecute(Bitmap bitmap) {
ImageView img = (ImageView) findViewById(R.id.img);
img.setImageBitmap(bitmap);
}
}
private InputStream OpenHttpConnection(String urlString)
throws IOException
{
InputStream in = null;
int response = -1;
URL url = new URL(urlString);
URLConnection conn = url.openConnection();
if (!(conn instanceof HttpURLConnection))
throw new IOException("Not an HTTP connection");
try{
HttpURLConnection httpConn = (HttpURLConnection) conn;
httpConn.setAllowUserInteraction(false);
httpConn.setInstanceFollowRedirects(true);
httpConn.setRequestMethod("GET");
httpConn.connect();
response = httpConn.getResponseCode();
if (response == HttpURLConnection.HTTP_OK) {
in = httpConn.getInputStream();
}
}
catch (Exception ex)
{
throw new IOException("Error connecting");
}
return in;
}
private Bitmap DownloadImage(String URL)
{
Bitmap bitmap = null;
InputStream in = null;
try {
in = OpenHttpConnection(URL);
bitmap = BitmapFactory.decodeStream(in);
in.close();
} catch (IOException e1) {
Toast.makeText(this, e1.getLocalizedMessage(),
Toast.LENGTH_LONG).show();
e1.printStackTrace();
}
return bitmap;
}
private String DownloadText(String URL)
{
int BUFFER_SIZE = 2000;
InputStream in = null;
try {
in = OpenHttpConnection(URL);
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
return "";
}
InputStreamReader isr = new InputStreamReader(in);
int charRead;
String str = "";
char[] inputBuffer = new char[BUFFER_SIZE];
try {
while ((charRead = isr.read(inputBuffer))>0)
{
//---convert the chars to a String---
String readString =
String.copyValueOf(inputBuffer, 0, charRead);
str += readString;
inputBuffer = new char[BUFFER_SIZE];
}
in.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
return "";
}
return str;
}
private void WordDefinition(String word) {
InputStream in = null;
try {
in = OpenHttpConnection("http://services.aonaware.com/DictService/DictService.asmx/Define?word=" + word);
Document doc = null;
DocumentBuilderFactory dbf =
DocumentBuilderFactory.newInstance();
DocumentBuilder db;
try {
db = dbf.newDocumentBuilder();
doc = db.parse(in);
} catch (ParserConfigurationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
doc.getDocumentElement().normalize();
//---retrieve all the <Definition> nodes---
NodeList definitionElements =
doc.getElementsByTagName("Definition");
String strDefinition = "";
for (int i = 0; i < definitionElements.getLength(); i++) {
Node itemNode = definitionElements.item(i);
if (itemNode.getNodeType() == Node.ELEMENT_NODE)
{
//---convert the Node into an Element---
Element definitionElement = (Element) itemNode;
//---get all the <WordDefinition> elements under
// the <Definition> element---
NodeList wordDefinitionElements =
(definitionElement).getElementsByTagName(
"WordDefinition");
strDefinition = "";
for (int j = 0; j < wordDefinitionElements.getLength(); j++) {
//---convert a <WordDefinition> Node into an Element---
Element wordDefinitionElement =
(Element) wordDefinitionElements.item(j);
//---get all the child nodes under the
// <WordDefinition> element---
NodeList textNodes =
((Node) wordDefinitionElement).getChildNodes();
//---get the first node, which contains the text---
strDefinition +=
((Node) textNodes.item(0)).getNodeValue() + ". ";
}
//---display the title---
Toast.makeText(getBaseContext(),strDefinition,
Toast.LENGTH_SHORT).show();
}
}
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
如果有人能详细解释，请帮助我们。
答案 0 :(得分：1)
OpenHttpConnection(
"http://services.aonaware.com/DictService/DictService.asmx/Define?word=" + word);
在这里，您实际上打开了一个 HTTP 连接到 Web服务，它通常以XML中编码的服务输出进行响应。其余的代码只是尝试解析这个XML响应数据。
doc = db.parse(in);
在这里，您使用Document将服务输出解析为DOM DocumentBuilder对象。文档对象用于遍历XML中存在的不同节点（您可以将它们视为<xmlTags>）。
因为，节点通常会重复以表示您通常将其作为NodeList检索的数据列表。
//---retrieve all the <Definition> nodes---
NodeList definitionElements =
doc.getElementsByTagName("Definition");
在这里，您只是检索XML响应中编码为<Definition>个节点的所有单词定义。 NodeList#getLength()为您提供了以后用于循环和处理它们的定义数。 NodeList#item(i)只是将指定索引处的定义作为Node对象返回。
同样，其余的处理只反映了您尝试解析的文档结构。它会因服务而异，或者只要服务更改其输出XML格式，您就需要更新它。查看org.w3c.dom的JavaDocs，了解代码用于解析此XML的所有不同类。
答案 1 :(得分：0)
首先，看看你实际在分析什么。您调用Web服务来定义单词，并返回该单词可用的所有定义。如果您查看服务的返回，是否为XML格式。在XML中，项目使用开始和结束标记定义。这显示在下面的代码段中，该代码片段来自于使用定义为cow的单词调用该Web服务。
<Definition>
<Word>cow</Word>
<Dictionary>
<Id>easton</Id>
<Name>Easton's 1897 Bible Dictionary</Name>
</Dictionary>
<WordDefinition>
Cow A cow and her calf were not to be killed on the same day (Lev. 22:28; Ex. 23:19; Deut. 22:6, 7). The reason for this enactment is not given. A state of great poverty is described in the words of Isa. 7:21-25, where, instead of possessing great resources, a man shall depend for the subsistence of himself and his family on what a single cow and two sheep could yield.
</WordDefinition>
</Definition>
<Definition>是开始标记，</Definition>是结束标记。您可以将开始和结束标记之间的任何内容视为节点。在这种情况下，代码将根据此XML中的数据构建节点列表。