Android 图片异步加载

所谓图片异步加载，意思是不用一次把图片全部加载完，你可以叫它延迟加载，缓冲加载都行。

看看你有没有这种需求：某篇文章图片很多，如果在载入文章时就载入所有图片，无疑会延缓载入速度，让用户等更久，所以，我想找这样一种插件，让网页只加载浏览器视野范围内的图片，没出现在范围内的图片就暂不加载，等用户滑动滚动条时再逐步加载。lazyload就是用来实现这种效果。

package com.example.demo1;import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;import EntityBen.GoodsItem;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Environment;
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 MyAdapter extends BaseAdapter {Context context ;ArrayList<GoodsItem> list ;int index ;public MyAdapter(Context con, ArrayList<GoodsItem> list) {super();this.context = con;this.list = list;}@Overridepublic int getCount() {// TODO Auto-generated method stubreturn list.size();}@Overridepublic Object getItem(int position) {// TODO Auto-generated method stubreturn list.get(position);}@Overridepublic long getItemId(int position) {// TODO Auto-generated method stubreturn 0;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {// TODO Auto-generated method stubindex =    position ;View view = convertView ;ViewHolder vH;if(view == null){System.out.println("dddddddddd"+context);LayoutInflater inflater = LayoutInflater.from(context);view = inflater.inflate(R.layout.tuangou_lv, null);vH = new ViewHolder();vH.name = (TextView) view.findViewById(R.id.goods_name);vH.info = (TextView) view.findViewById(R.id.goods_infor);vH.costPrice = (TextView) view.findViewById(R.id.cost_price);vH.oriPrice = (TextView) view.findViewById(R.id.ori_price);vH.moods = (TextView) view.findViewById(R.id.moods);vH.imgtask = (ImageView) view.findViewById(R.id.goods_img);view.setTag(vH);}elsevH = (ViewHolder) view.getTag();vH.name.setText(list.get(position).getName());vH.info.setText(list.get(position).getInfo());vH.costPrice.setText(list.get(position).getCostprice() + "");vH.oriPrice.setText(list.get(position).getOriprice() + "");vH.moods.setText(list.get(position).getMoods() + "人");//当前行的图片路径 例如：http://192.168.0.148:9999/Music/aaa.jpgString fileurl = list.get(position).getImageUrl();//文件操作类实例化FileUtils f = new FileUtils();//通过字符串操作获得当前的图片名称 ( aaa.jpg)String fileName = fileurl.substring(fileurl.lastIndexOf("/") + 1);// /mnt/sdcard/tt/aaa.jpgString filePath = f.GetSDPATH() + "tt/"+fileName;//验证当前图片是否已经存在 /mnt/sdcard/tt/ 中if(f.IsFileExists("tt/"+fileName)){//如果存在vH.imgtask.setImageBitmap(BitmapFactory.decodeFile(filePath));}else{//如果不存在vH.downloadImage=new DownLoadImage(vH.imgtask);vH.downloadImage.execute(list.get(position).getImageUrl());}return view;}public static class ViewHolder{private DownLoadImage downloadImage ;private ImageView  imgtask;private TextView name , info , costPrice ,oriPrice , moods;}private class  DownLoadImage extends AsyncTask<String, Void, Bitmap>{Bitmap drawable;ImageView imageView;DownLoadImage (ImageView img){this.imageView=img;}/*** 此函数相当于 run函数*/@Overrideprotected Bitmap doInBackground(String... params) {DownImg fileDownload=new DownImg();  //调用图片下载函数，将图片下载到本地，并返回此图片的本地路径String TalkPath = fileDownload.DownLoadFile(params[0], "tt");drawable = BitmapFactory.decodeFile(TalkPath);return drawable; //相当于 Message}/*** 当任务执行之前开始调用此方法，可以在这里显示进度对话框*/@Overrideprotected void onPreExecute() {super.onPreExecute();System.out.println("异步加载开始了");}/*** 此方法在主线程执行，任务执行的结果作为此方法的参数返回。*/@Overrideprotected void onPostExecute(Bitmap result) {// TODO Auto-generated method stubsuper.onPostExecute(result);System.out.println("异步执行完毕了，返回");if (result!=null) {imageView.setImageBitmap(drawable);}}}public class DownImg {HttpURLConnection httpconn = null;public String DownLoadFile(String fileurl, String path) {InputStream inputStream = null;OutputStream outputStream = null;File file = null;String fileName = "";String imgPath = "";try {fileName = fileurl.substring(fileurl.lastIndexOf("/") + 1);FileUtils fileUtils = new FileUtils();imgPath =fileUtils.GetSDPATH() +  path + "/" + fileName;System.out.println(fileurl + "   " + imgPath);if (fileUtils.IsFileExists(path + "/" + fileName)) {System.out.println("已存在此图片，无需下载");return imgPath;}URL url = new URL(fileurl);// 获得或者确定下载的路径HttpURLConnection httpconnCon = (HttpURLConnection) url.openConnection();inputStream = httpconnCon.getInputStream();// 获得字节流fileUtils.CreateSDDir(path);// 确定下载路径（创建你需要的文件夹）file = fileUtils.CreateSDFile(path + "/" + fileName);System.out.println("ddddd---" + file);outputStream = new FileOutputStream(file);byte buffer[] = new byte[4 * 1024];int length = 0;while ((length = inputStream.read(buffer)) != -1) {outputStream.write(buffer, 0, length);}outputStream.flush();} catch (Exception e) {return null;} finally {try {// inputStream.close();// outputStream.close();} catch (Exception e2) {e2.printStackTrace();}}return imgPath;}}public class FileUtils {private String SDPATH;public FileUtils() {SDPATH = Environment.getExternalStorageDirectory() + "/";//"/mnt/sdcard/"}/*** 获得当前系统的SDPATH路径字符* */public String GetSDPATH() {return SDPATH;}/*** 在SD卡上创建文件* */public File CreateSDFile(String fileName) throws IOException {File file = new File(SDPATH + fileName);boolean isCreate = file.createNewFile();return file;}/*** 在SD卡上创建文件夹* */public File CreateSDDir(String dirName) {File file = new File(SDPATH + dirName);boolean isCreateDir = file.mkdir();return file;}/*** 判断文件是否存在* */public boolean IsFileExists(String fileName) {//"/mnt/sdcard/hhh/aaa.mp3"File file = new File(SDPATH + fileName);return file.exists();}}}

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