ListView优化的模型示意图
实例代码：
业务逻辑代码：
package com.hsj.example.asyncloadxmldatademo08;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import com.hsj.example.asyncloadxmldatademo08.hsj.domain.Person;
import com.hsj.example.asyncloadxmldatademo08.hsj.utils.NetUtils;
import java.io.InputStream;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private ListView listView_persons;
private MyAdapter adapter;
private List<Person> personList;
private ProgressDialog progressDialog;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.progressDialog=new ProgressDialog(this);
this.progressDialog.setMessage("正在加载网络数据,请稍等......");
this.progressDialog.setCancelable(true);
this.listView_persons= (ListView) this.findViewById(R.id.listView_persons);
String path = "http://10.211.55.4:8080/persons.xml";
new LoadNetDataAsyncTask().execute(path);
}
private final class LoadNetDataAsyncTask extends AsyncTask<String,Void,List<Person>> {
@Override
protected void onPreExecute() {
progressDialog.show();
}
@Override
protected List<Person> doInBackground(String... params) {
try {
InputStream inputStream= NetUtils.getInputStreamByPath(params[0]);
if(inputStream!=null){
String json= NetUtils.getStringByInputStream(inputStream);
if(json!=null){
return NetUtils.getPersonsByXmlString(json);
}
}
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(List<Person> persons) {
adapter=new MyAdapter(persons);
listView_persons.setAdapter(adapter);
progressDialog.dismiss();
}
}
private final class MyAdapter extends BaseAdapter {
private List<Person> personList;
private ViewHolder viewHolder;
public MyAdapter(List<Person> personList) {
this.personList=personList;
}
@Override
public int getCount() {
return personList.size();
}
@Override
public Object getItem(int position) {
return personList.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
//1.得到数据
Person person=personList.get(position);
if(convertView==null){
viewHolder=new ViewHolder();
convertView=View.inflate(MainActivity.this,R.layout.person_item,null);
viewHolder.imageView_header= (ImageView) convertView.findViewById(R.id.imageView_header);
viewHolder.textView_name= (TextView) convertView.findViewById(R.id.textView_name);
viewHolder.textView_age= (TextView) convertView.findViewById(R.id.textView_age);
convertView.setTag(viewHolder);
}else{
viewHolder= (ViewHolder) convertView.getTag();
}
//解决图片错位问题
final String cover=person.getHeader();
viewHolder.imageView_header.setTag(cover);
//viewHolder.imageView_header.setImageBitmap(person.getHeader());
class LoadImageAsyncTask extends AsyncTask<String,Void,Bitmap>{
@Override
protected Bitmap doInBackground(String... params) {
try {
InputStream inputStream=NetUtils.getInputStreamByPath(params[0]);
if(inputStream!=null){
return BitmapFactory.decodeStream(inputStream);
}
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
if(bitmap!=null && viewHolder.imageView_header.getTag()!=null && cover.equals(viewHolder.imageView_header.getTag())){
viewHolder.imageView_header.setImageBitmap(bitmap);
}
}
}
new LoadImageAsyncTask().execute(person.getHeader());
viewHolder.textView_name.setText(person.getName());
viewHolder.textView_age.setText(String.valueOf(person.getAge()));
return convertView;
}
}
class ViewHolder{
ImageView imageView_header;
TextView textView_name;
TextView textView_age;
}
}
工具类代码：
package com.hsj.example.asyncloadxmldatademo08.hsj.utils;
import android.util.Xml;
import com.hsj.example.asyncloadxmldatademo08.hsj.domain.Person;
import org.xmlpull.v1.XmlPullParser;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.StringReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
/**
* Created by hsjwcf on 2018/6/1.
*/
public class NetUtils {
/**
* 根据网址得到输入流对象
* @param path
* @return
*/
public static InputStream getInputStreamByPath(String path) throws Exception {
URL url=new URL(path);
HttpURLConnection httpURLConnection= (HttpURLConnection) url.openConnection();
httpURLConnection.setConnectTimeout(3000);
int responseCode=httpURLConnection.getResponseCode();
if(responseCode==HttpURLConnection.HTTP_OK){
return httpURLConnection.getInputStream();
}
return null;
}
/**
* 通过 InputStream 得到字节数组
* @param inputStream
* @return
*/
public static byte[] getByteArrayByInputStream(InputStream inputStream) throws IOException {
ByteArrayOutputStream byteArrayOutputStream=new ByteArrayOutputStream();
byte[] buffer=new byte[1024];
int len=0;
while ((len=inputStream.read(buffer))!=-1){
byteArrayOutputStream.write(buffer,0,len);
}
return byteArrayOutputStream.toByteArray();
}
/**
* 将输入流转换成字符串
* @param inputStream
* @return
* @throws IOException
*/
public static String getStringByInputStream(InputStream inputStream) throws IOException {
return new String(getByteArrayByInputStream(inputStream));
}
/**
* 面试题:市面上常用的解析XML的技术有哪些?
* DOM
* SAX
* JDOM
* DOM4J
* PULL(android 自带的解析Xml的技术)
*
* @param xml
* @return
* @throws Exception
*/
public static List<Person> getPersonsByXmlString(String xml) throws Exception {
List<Person> persons=null;
/*
PULL 基于事件驱动的解析方式
*/
//1.得到Pull解析器对象
XmlPullParser xmlPullParser= Xml.newPullParser();
//2.设置需要解析的Xml 数据
xmlPullParser.setInput(new StringReader(xml));
//3.得到事件对象
int eventType= xmlPullParser.getEventType();
System.out.println("eventType="+eventType);
Person person=null;
//XmlPullParser.END_DOCUMENT=1
while (eventType!=XmlPullParser.END_DOCUMENT){
switch (eventType){
//XmlPullParser.START_DOCUMENT=0:开始解析Xml时执行,而且只执行一次
case XmlPullParser.START_DOCUMENT:
persons=new ArrayList<>();
System.out.println("==START_DOCUMENT===");
break;
//XmlPullParser.START_TAG=2:遇到开始标签时执行
case XmlPullParser.START_TAG:
//xmlPullParser.getName():得到标签名
String startTag=xmlPullParser.getName();
if("person".equals(startTag)){
person=new Person();
//根据索引值得到属性值,索引值从0开始
//String id=xmlPullParser.getAttributeValue(0);
//根据属性名得到属性值
String id=xmlPullParser.getAttributeValue(null,"id");
System.out.println("id="+id);
}else if("name".equals(startTag)){
//得到当前标签后面的文本内容,同时事件值向后推动了一下
String name=xmlPullParser.nextText();
person.setName(name);
System.out.println("name="+name);
}else if("age".equals(startTag)){
String age=xmlPullParser.nextText();
person.setAge(Integer.parseInt(age));
System.out.println("age="+age);
}else if("header".equals(startTag)){
String header=xmlPullParser.nextText();
person.setHeader(header);
persons.add(person);
System.out.println("header="+header);
}
System.out.println("===START_TAG="+startTag+"==");
break;
}
//修改事件值
eventType=xmlPullParser.next();
}
System.out.println("persons="+persons);
return persons;
}
}