Android 圖片異步加載

所謂圖片異步加載，意思是不用一次把圖片全部加載完，你可以叫它延遲加載，緩沖加載都行。

看看你有沒有這種需求：某篇文章圖片很多，如果在載入文章時就載入所有圖片，無疑會延緩載入速度，讓用戶等更久，所以，我想找這樣一種插件，讓網頁只加載瀏覽器視野范圍內的圖片，沒出現在范圍內的圖片就暫不加載，等用戶滑動滾動條時再逐步加載。lazyload就是用來實現這種效果。

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;
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
      index =   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);

        }else
            vH = (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");



        //當前行的圖片路徑 例如：http://192.168.0.148:9999/Music/aaa.jpg
                String fileurl = list.get(position).getImageUrl();
                //文件操作類實例化
                FileUtils f = new FileUtils();
                //通過字符串操作獲得當前的圖片名稱 ( aaa.jpg)
                String fileName = fileurl.substring(fileurl.lastIndexOf("/") + 1);
                // /mnt/sdcard/tt/aaa.jpg
                String filePath = f.GetSDPATH() + "tt/"+fileName;
                //驗證當前圖片是否已經存在 /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;
        }
        /**
         * 此函數相當于 run函數
         */
        @Override
        protected Bitmap doInBackground(String... params) {
            DownImg fileDownload=new DownImg(); 
            //調用圖片下載函數，將圖片下載到本地，并返回此圖片的本地路徑
             String TalkPath = fileDownload.DownLoadFile(params[0], "tt");

             drawable = BitmapFactory.decodeFile(TalkPath);
            return drawable; //相當于 Message
        }

        /**
         * 當任務執行之前開始調用此方法，可以在這里顯示進度對話框
         */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            System.out.println("異步加載開始了");
        }



        /**
         * 此方法在主線程執行，任務執行的結果作為此方法的參數返回。
         */
        @Override
        protected void onPostExecute(Bitmap result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            System.out.println("異步執行完畢了，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("已存在此圖片，無需下載");
                    return imgPath;
                }
                URL url = new URL(fileurl);// 獲得或者確定下載的路徑
                HttpURLConnection httpconnCon = (HttpURLConnection) url
                        .openConnection();
                inputStream = httpconnCon.getInputStream();// 獲得字節流
                fileUtils.CreateSDDir(path);// 確定下載路徑（創建你需要的文件夾）
                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/"
        }

        /**
         * 獲得當前系統的SDPATH路徑字符
         * */
        public String GetSDPATH() {
            return SDPATH;
        }

        /**
         * 在SD卡上創建文件
         * */
        public File CreateSDFile(String fileName) throws IOException {
            File file = new File(SDPATH + fileName);
            boolean isCreate = file.createNewFile();
            return file;
        }

        /**
         * 在SD卡上創建文件夾
         * */
        public File CreateSDDir(String dirName) {
            File file = new File(SDPATH + dirName);
            boolean isCreateDir = file.mkdir();
            return file;
        }

        /**
         * 判斷文件是否存在
         * */
        public boolean IsFileExists(String fileName) {
            //"/mnt/sdcard/hhh/aaa.mp3"
            File file = new File(SDPATH + fileName);
            return file.exists();
        }


    }

}