ViewHolder的使用

使用listView的时候，通过ViewHolder进行缓存可以提升性能

JavaBean,创建了News对象的几个参数title,detail,comment,imageUrl

package com.ldw.newsView.domain;public class News {private String title;private String detail;private String comment;private String iamgeUrl;public String getTitle() {return title;}public void setTitle(String title) {this.title = title;}public String getDetail() {return detail;}public void setDetail(String detail) {this.detail = detail;}public String getComment() {return comment;}public void setComment(String comment) {this.comment = comment;}public String getIamgeUrl() {return iamgeUrl;}public void setIamgeUrl(String iamgeUrl) {this.iamgeUrl = iamgeUrl;}@Overridepublic String toString() {return "News [title=" + title + ", detail=" + detail + ", comment="+ comment + ", iamgeUrl=" + iamgeUrl + "]";}}

布局文件

activity_main.xml主布局，用ListView进行填充

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"android:paddingBottom="@dimen/activity_vertical_margin"android:paddingLeft="@dimen/activity_horizontal_margin"android:paddingRight="@dimen/activity_horizontal_margin"android:paddingTop="@dimen/activity_vertical_margin"tools:context=".MainActivity" ><ListViewandroid:id="@+id/lv"android:layout_width="match_parent"android:layout_height="match_parent"/></RelativeLayout>

ListView的布局文件，每一个的布局

item_listview.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent" ><com.loopj.android.image.SmartImageView android:id="@+id/siv"android:layout_height="90sp"android:layout_width="70sp"android:src="@drawable/ic_launcher"android:layout_centerVertical="true"/><TextViewandroid:id="@+id/tv_title"android:layout_width="match_parent"android:layout_height="wrap_content"android:text="XX"android:layout_toRightOf="@id/siv"android:textSize="22sp"android:singleLine="true"/><TextViewandroid:id="@+id/tv_detail"android:layout_width="match_parent"android:layout_height="wrap_content"android:text="Xomatic Target Mode: using existing emulator 'emulator-5554' running compatible AVD 'ldd'omatic Target Mode: using existing emulator 'emulator-5554' running compatible AVD 'ldd'X"android:layout_toRightOf="@id/siv"android:textSize="14sp"android:textColor="@android:color/darker_gray"android:layout_below="@id/tv_title"android:lines="2"/><TextView android:id="@+id/tv_comment"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="213评论"android:textColor="#ff0000"android:layout_alignParentRight="true"android:layout_below="@id/tv_detail"/></RelativeLayout>

主布局文件，首先调用getNewsInfo利用子线程来请求xml并解析xml文件中的元素，同时把元素放在List<News>对象中，然后在setAdapter中来通过ViewHolder来获取到List中的News对象来解析每一条的元素，并进行显示

package com.ldw.newsView;import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;import org.xmlpull.v1.XmlPullParser;import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.util.Xml;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;import com.ldw.newsView.domain.News;
import com.loopj.android.image.SmartImageView;public class MainActivity extends Activity {List<News> newsList;Handler handler = new Handler(){public void handleMessage(android.os.Message msg){ListView lv = (ListView) findViewById(R.id.lv);lv.setAdapter(new MyAdapter());}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);getNewsInfo();//ListView lv = (ListView) findViewById(R.id.lv);//需保证解析结束以后，再设置适配器//lv.setAdapter(new MyAdapter());}class MyAdapter extends BaseAdapter{//得到元素的数量，确定listView条目的数量@Overridepublic int getCount() {// TODO Auto-generated method stubreturn newsList.size();}@Overridepublic Object getItem(int position) {// TODO Auto-generated method stubreturn null;}@Overridepublic long getItemId(int position) {// TODO Auto-generated method stubreturn 0;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {News news = newsList.get(position);View v = null;ViewHolder mHolder;if(convertView == null){v = View.inflate(MainActivity.this, R.layout.item_listview, null);//布局文件中所有组件的对象封装到ViewHolder对象中mHolder = new ViewHolder();mHolder.tv_title = (TextView) v.findViewById(R.id.tv_title);mHolder.tv_detail = (TextView) v.findViewById(R.id.tv_detail);mHolder.tv_comment = (TextView) v.findViewById(R.id.tv_comment);mHolder.siv = (SmartImageView) v.findViewById(R.id.siv);//把ViewHolder对象封装到View对象中v.setTag(mHolder);}else{v = convertView;mHolder = (ViewHolder) v.getTag();}mHolder.tv_title.setText(news.getTitle());mHolder.tv_detail.setText(news.getDetail());mHolder.tv_comment.setText(news.getComment() + "条评论");mHolder.siv.setImageUrl(news.getIamgeUrl());/*TextView tv_title = (TextView) v.findViewById(R.id.tv_title);tv_title.setText(news.getTitle());TextView tv_detail = (TextView) v.findViewById(R.id.tv_detail);tv_detail.setText(news.getDetail());TextView tv_comment = (TextView) v.findViewById(R.id.tv_comment);tv_comment.setText(news.getComment() + "条评论");SmartImageView siv = (SmartImageView) v.findViewById(R.id.siv); siv.setImageUrl(news.getIamgeUrl());*/return v;}class ViewHolder{//条目的布局文件中有什么组件，这里就定义有什么属性TextView tv_title;TextView tv_comment;TextView tv_detail;SmartImageView siv;}}private void getNewsInfo(){Thread t = new Thread(){@Overridepublic void run(){String path="http://192.168.0.102:8080/news.txt";try {URL url = new URL(path);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setRequestMethod("GET");conn.setConnectTimeout(5000);conn.setReadTimeout(5000);//发送http请求，获取相应的状态吗if(conn.getResponseCode() == 200){InputStream is = conn.getInputStream();//使用pull解析器解析is流parseNewsXml(is);}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}};t.start();}private void parseNewsXml(InputStream is){XmlPullParser xp = Xml.newPullParser();try {xp.setInput(is, "utf-8");//对节点的事件类型进行判断，可以知道当前的节点类型int type = xp.getEventType();News news = null;while(type != XmlPullParser.END_DOCUMENT){switch(type){case XmlPullParser.START_TAG:if("newsList".equals(xp.getName())){newsList = new ArrayList<News>();}else if("news".equals(xp.getName())){news = new News();}else if("title".equals(xp.getName())){String title = xp.nextText();news.setTitle(title);}else if("detail".equals(xp.getName())){String detail = xp.nextText();news.setDetail(detail);}else if("comment".equals(xp.getName())){String comment = xp.nextText();news.setComment(comment);}else if("image".equals(xp.getName())){String image = xp.nextText();news.setIamgeUrl(image);}break;case XmlPullParser.END_TAG:if("news".equals(xp.getName())){newsList.add(news);}break;}//解析玩借点以后，把指针移动到下一个节点，返回他的时间类型type = xp.next();}//发消息让主线程设置listView适配器,因为消息不需要携带数据，发送空消息handler.sendEmptyMessage(1);for(News n : newsList){System.out.println(n.toString());}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}

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