Android学习笔记之网络图片加载

三种方式：

1、new Thread       加载到的图片会出现错位的现象，本来该显示在第二的图片也许会显示到第一，且每次都要加载，耗流量

2、AsyncTask + LruCache     解决了图片显示错位问题，和缓存问题，缺点是代码写起来太繁琐

3、FinalBitmap     代码简洁且图片可正常显示和缓存

1、new Thread方法异步加载图片

package com.example.logintest;import java.io.InputStream;import java.net.URL;import java.util.ArrayList;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ImageView;import android.widget.TextView;public class GuildAdapter extends BaseAdapter {private ArrayList<DefineClass> list;private LayoutInflater inflater;private Bitmap bitmap;GuildAdapter(Context context,ArrayList<DefineClass> list) {this.inflater = LayoutInflater.from(context);this.list = list;}@Overridepublic int getCount() {return list.size();}@Overridepublic Object getItem(int position) {return position;}@Overridepublic long getItemId(int position) {return position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {ViewHolder holder;if(convertView == null) {holder = new ViewHolder();convertView = this.inflater.inflate(R.layout.guild_list, null);holder.picima = (ImageView)convertView.findViewById(R.id.guildima);holder.nametxt = (TextView)convertView.findViewById(R.id.name);holder.numbertxt = (TextView)convertView.findViewById(R.id.number);holder.Notxt = (TextView)convertView.findViewById(R.id.No);holder.introductiontxt = (TextView)convertView.findViewById(R.id.guildintroduction);convertView.setTag(holder);} else {holder = (ViewHolder) convertView.getTag();}final DefineClass bean = list.get(position);String url = bean.getpic();<span style="color:#993399;">holder.picima.setImageBitmap(GetBitmap(url));</span>holder.nametxt.setText(bean.getname());holder.numbertxt.setText(bean.getnumber());holder.Notxt.setText(bean.getNo());holder.introductiontxt.setText(bean.getintroduction());return convertView;}public class ViewHolder {TextView nametxt,introductiontxt,numbertxt,Notxt;ImageView picima;}<span style="color:#993399;">private Bitmap GetBitmap(final String url) {new Thread(new Runnable() {@Overridepublic void run() {try {URL urls = new URL(url);InputStream is = urls.openStream();bitmap = BitmapFactory.decodeStream(is);} catch (Exception e) {e.printStackTrace();}}}).start();return bitmap;}</span>}

2、AsyncTask+LruCache下载缓存图片

package com.example.logintest;import java.io.BufferedInputStream;import java.io.IOException;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;import android.annotation.SuppressLint;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.support.v4.util.LruCache;import android.widget.ImageView;@SuppressLint("NewApi")public class LoadImageThread {private LruCache<String,Bitmap> mcaches;LoadImageThread() {//构造函数    <span style="color:#993399;">此处主要对LruCache缓存进行了初步设置</span>int maxMemory = (int)Runtime.getRuntime().maxMemory();  <span style="color:#993399;">获取最大可用内存</span>int cacheSize = maxMemory / 4;  <span style="color:#993399;">设定缓存大小</span>mcaches = new LruCache<String,Bitmap>(cacheSize) { <span style="color:#993399;">初始化LruCache,每次存入缓存的时候调用，返回bitmap的大小</span>@Overrideprotected int sizeOf(String key, Bitmap value) {return value.getByteCount();}};}//主要方法，在特定的url下下载图片，并给imageview设置图片public void ImageAsyncTask(ImageView iv,String url) {Bitmap bitmap = mcaches.get(url); //从缓存中取出图片if(bitmap == null) {//缓存中没有图片new myAsyncTask(iv,url).execute(url);  //AsyncTask下载图片} else {iv.setImageBitmap(bitmap); //直接将缓存中的图片设置显示}}private class myAsyncTask extends AsyncTask<String,Void,Bitmap> { <span style="color:#993399;"> AsyncTask异步加载</span>private String murl;private ImageView mimg;public myAsyncTask(ImageView iv,String url) {   <span style="color:#993399;">这一部分是为了给控件设置要显示的图片</span>mimg = iv;murl = url;}@Overrideprotected Bitmap <span style="color:#993399;">doInBackground</span>(String... params) { <span style="color:#993399;">此方法必须在这里重写，异步执行后台将要完成的任务。</span>//从网络上获取图片Bitmap bitmap = getImage(params[0]); //调用getImage方法下载图片String url = params[0];if(bitmap != null) {//将获取到的图片加入缓存addBitmaptoCache(url,bitmap);}return bitmap;}@Overrideprotected void onPostExecute(Bitmap result) { //为主线程设置显示的图片super.onPostExecute(result);if(mimg.getTag().equals(murl)) {mimg.setImageBitmap(result);}}}//给缓存中添加数据public void addBitmaptoCache(String url,Bitmap bitmap) {if(mcaches.get(url) == null) {   //判断缓存中是否空mcaches.put(url, bitmap);    //为空，则设置数据}}private Bitmap getImage(String url) { //被调用的下载图片方法HttpURLConnection connection;InputStream in = null;URL urls;Bitmap bitmap = null;try {urls = new URL(url);connection = (HttpURLConnection) urls.openConnection();in = connection.getInputStream();BufferedInputStream buffer = new BufferedInputStream(in);bitmap = BitmapFactory.decodeStream(buffer);connection.disconnect();} catch (MalformedURLException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {try {in.close();} catch (IOException e) {e.printStackTrace();}}return bitmap;}}

设置图片显示：

package com.example.logintest;import java.util.List;import net.tsz.afinal.FinalBitmap;import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ImageView;import android.widget.TextView;public class GuildAdapter extends BaseAdapter {private List<DefineClass> mlist;private LayoutInflater inflater;private LoadImageThread loadimage;GuildAdapter(Context context,List<DefineClass> list) {this.inflater = LayoutInflater.from(context);this.mlist = list;loadimage = new LoadImageThread();}@Overridepublic int getCount() {return mlist.size();}@Overridepublic Object getItem(int position) {return mlist.get(position);}@Overridepublic long getItemId(int position) {return position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {ViewHolder holder;if(convertView == null) {holder = new ViewHolder();convertView = this.inflater.inflate(R.layout.guild_list, null);<span style="color:#993399;">holder.picimg = (ImageView)convertView.findViewById(R.id.guildima);</span>holder.nametxt = (TextView)convertView.findViewById(R.id.name);holder.numbertxt = (TextView)convertView.findViewById(R.id.number);holder.Notxt = (TextView)convertView.findViewById(R.id.No);holder.introductiontxt = (TextView)convertView.findViewById(R.id.guildintroduction);convertView.setTag(holder);} else {holder = (ViewHolder) convertView.getTag();}DefineClass bean = new DefineClass();  <span style="color:#993399;">一个DefineClass实体，主要利用</span><span style="color: rgb(153, 51, 153); font-family: Arial, Helvetica, sans-serif;">bean.picurl给</span><span style="color: rgb(153, 51, 153); font-family: Arial, Helvetica, sans-serif;">loadimage.ImageAsyncTask(holder.picimg, bean.picurl);传递url图片的网络地址</span><span style="color: rgb(153, 51, 153); font-family: Arial, Helvetica, sans-serif;"></span><span style="color:#993399;"></span>bean = mlist.get(position);holder.picimg.setTag(bean.picurl);loadimage.ImageAsyncTask(holder.picimg, bean.picurl); <span style="color:#993399;">调用上面的类<span style="font-family: Arial, Helvetica, sans-serif;">LoadImageThread 的ImageAsyncTask方法</span></span>holder.nametxt.setText(bean.name);holder.numbertxt.setText(bean.number);holder.Notxt.setText(bean.No);holder.introductiontxt.setText(bean.introduction);return convertView;}public class ViewHolder {TextView nametxt,introductiontxt,numbertxt,Notxt;<span style="color:#993399;">ImageView picimg;</span>}}

3、FinalBitmap

很方便的就可以实现上面两个类合在一起的功能，当然还得需要afinal-master包  （Copyright (c) 2012-2013, Michael Yang 杨福海 (www.yangfuhai.com)）

package com.example.logintest;import java.util.List;import net.tsz.afinal.FinalBitmap;import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ImageView;import android.widget.TextView;public class GuildAdapter extends BaseAdapter {private List<DefineClass> mlist;private LayoutInflater inflater;//private LoadImageThread loadimage;<span style="color:#993399;">private FinalBitmap fb;</span>GuildAdapter(Context context,List<DefineClass> list) {this.inflater = LayoutInflater.from(context);this.mlist = list;//loadimage = new LoadImageThread();<span style="color:#993399;">this.fb = FinalBitmap.create(context);</span>}@Overridepublic int getCount() {return mlist.size();}@Overridepublic Object getItem(int position) {return mlist.get(position);}@Overridepublic long getItemId(int position) {return position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {ViewHolder holder;if(convertView == null) {holder = new ViewHolder();convertView = this.inflater.inflate(R.layout.guild_list, null);holder.picimg = (ImageView)convertView.findViewById(R.id.guildima);holder.nametxt = (TextView)convertView.findViewById(R.id.name);holder.numbertxt = (TextView)convertView.findViewById(R.id.number);holder.Notxt = (TextView)convertView.findViewById(R.id.No);holder.introductiontxt = (TextView)convertView.findViewById(R.id.guildintroduction);convertView.setTag(holder);} else {holder = (ViewHolder) convertView.getTag();}DefineClass bean = new DefineClass();bean = mlist.get(position);holder.picimg.setTag(bean.picurl);//loadimage.ImageAsyncTask(holder.picimg, bean.picurl);<span style="color:#993399;">holder.picimg.setImageResource(R.drawable.def_grid_zz_list);   if(holder.picimg.getTag() != null && holder.picimg.getTag() == bean.picurl) {fb.display(holder.picimg, bean.picurl);}</span>holder.nametxt.setText(bean.name);holder.numbertxt.setText(bean.number);holder.Notxt.setText(bean.No);holder.introductiontxt.setText(bean.introduction);return convertView;}public class ViewHolder {TextView nametxt,introductiontxt,numbertxt,Notxt;ImageView picimg;}}