从网络获取图片，并缓存到SD卡

效果图：



图片存在bmob(http://www.bmob.com )后台，所以下载Demo运行的话要到官网申请 Application ID。
先点击上传图片，再点击缓存图片，不然没数据。


代码：

1. paths=new String[5];
   
2. for(int i=0;i<5;i++){
   
3.         //图片路径
   
4.         paths[i]=Environment.getExternalStorageDirectory()+"/"+i+".jpg";        
   
5.   }

复制代码

上面的代码要改为自己的图片路径。

主要代码：

IndexActivity

public class IndexActivity extends Activity {

        private String[] paths;
        private int j;
        private File cache;
        private String appid="";  //你的Application ID

        protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                Bmob.initialize(this, appid);
                setContentView(R.layout.activity_index);

                ///创建缓存目录
                cache=new File(Environment.getExternalStorageDirectory(),"cache");   
                if(!cache.exists()){
                        cache.mkdirs();
                }
        }

        public void skip(View v){
                Intent intent=new Intent(this,MainActivity.class);
                startActivity(intent);
        }

        public void upload(View v){
                paths=new String[5];
                for(int i=0;i<5;i++){
                        //图片路径
                        paths[i]=Environment.getExternalStorageDirectory()+"/"+i+".jpg";        
                }

                //批量上传图片
                Bmob.uploadBatch(this, paths, new UploadBatchListener() {

                        @Override
                        public void onSuccess(List<BmobFile> arg0, List<String> arg1) {
                                // TODO Auto-generated method stub
                                String strurl="";
                                for(String url:arg1){
                                        strurl=url;
                                }
                                Person p=new Person();
                                p.setIcPath(strurl);
                                p.setStr("s"+j);
                                p.save(IndexActivity.this);
                                j++;
                                toast("第"+j+"个上传成功！");
                        }

                        @Override
                        public void onProgress(int curIndex, int curPercent, int total, int totalPercent) {
                                // TODO Auto-generated method stub

                                //1、curIndex--表示当前第几个文件正在上传
                                //2、curPercent--表示当前上传文件的进度值（百分比）
                                //3、total--表示总的上传文件数
                                //4、totalPercent--表示总的上传进度（百分比）
                                MyUtil.logI(curIndex+" "+curPercent+" "+total+" "+totalPercent);
                                
                        }

                        @Override
                        public void onError(int arg0, String arg1) {
                                // TODO Auto-generated method stub
                                toast("error "+arg1);
                                MyUtil.logI("errer "+arg1);
                        }
                });
        }
        
        // 清理缓存
        public void clear(View v){
                if(cache.length()!=0){
                        File[] files=cache.listFiles();
                        for(File file:files){
                                file.delete();
                        }
                        cache.delete();
                        toast("缓存清理成功");
                }else{
                        toast("暂无缓存");
                }
        }

        public void toast(String msg){
                Toast.makeText(this, msg, Toast.LENGTH_SHORT).show();
        }

}

MainActivity

1. public class MainActivity extends Activity {
   
           private ListView lv;
           private MyAdapter adapter;
           private File cache;
           private List<Person> list;
           protected void onCreate(Bundle savedInstanceState) {
                   super.onCreate(savedInstanceState);
                   setContentView(R.layout.activity_main);
                   initView();
           }
   
           private void initView() {
                   // TODO Auto-generated method stub
                   lv=(ListView)findViewById(R.id.listView1);
                   list=new ArrayList<Person>();
                   
                   cache=new File(Environment.getExternalStorageDirectory(),"cache");
                   if(!cache.exists()){
                           cache.mkdirs();
                   }
                   
                   getData();
           }
   
           private void getData() {
                   // TODO Auto-generated method stub
                   //查询数据
                   BmobQuery<Person> bq=new BmobQuery<Person>();
                   bq.setCachePolicy(CachePolicy.CACHE_ELSE_NETWORK);        //缓存查询
                   bq.findObjects(this, new FindListener<Person>() {
                           
                           @Override
                           public void onSuccess(List<Person> arg0) {
                                   // TODO Auto-generated method stub
                                   list=arg0;
                                   adapter=new MyAdapter(MainActivity.this, list, cache);
                                   lv.setAdapter(adapter);
                           }
                           
                           @Override
                           public void onError(int arg0, String arg1) {
                                   // TODO Auto-generated method stub
                                   MyUtil.logI("errer "+arg1);
                           }
                   });
           }

   
   
   

MyAdapter

1. public class MyAdapter extends BaseAdapter {
           private Context context;
           private List<Person> list;
           private File cache;
           public MyAdapter(Context context, List<Person> list, File cache) {
                   this.context = context;
                   this.list = list;
                   this.cache = cache;
           }
   
           @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 position;
           }
   
           @Override
           public View getView(int position, View convertView, ViewGroup parent) {
                   // TODO Auto-generated method stub
                   ViewHolder vh;
                   if(convertView==null){
                           convertView=LayoutInflater.from(context).inflate(R.layout.item, null);
                           vh=new ViewHolder();
                           vh.tv=(TextView)convertView.findViewById(R.id.tv);
                           vh.iv=(ImageView)convertView.findViewById(R.id.iv);
                           convertView.setTag(vh);
                   }else{
                           vh=(ViewHolder)convertView.getTag();
                   }
                   
                   final Person p=list.get(position);
                   vh.tv.setText(p.getStr());
                   
                   // 异步的加载图片
                   MyUtil mu=new MyUtil();
                   AsyncImageTask as=new AsyncImageTask(mu,vh.iv,cache);
                   if(p.getIcPath()!=null){
                           as.execute(p.getIcPath());
                   }else{
                           vh.iv.setImageResource(R.drawable.ic_launcher);
                   }
                   
                   return convertView;
           }
   
           class ViewHolder{
                   TextView tv;
                   ImageView iv;
           }
           
   }

   
   
   

MyUtil

1. public class MyUtil {
           /**
            * 从网络上获取图片，如果图片在本地存在的话就直接拿，如果不存在再去服务器上下载图片
            * */
           public Uri getImageURI(String path,File cache) throws Exception{
                   String name=MD5.getMD5(path)+path.substring(path.lastIndexOf("."));
                   logI("name"+name);
                   File file=new File(cache, name);
                   // 如果图片存在本地缓存目录，则不去服务器下载
                   if(file.exists()){
                           logI("cache");
                           return Uri.fromFile(file);
                   }else{
                           URL url=new URL(path);
                           HttpURLConnection conn=(HttpURLConnection)url.openConnection();
                           conn.setConnectTimeout(5000);
                           conn.setRequestMethod("GET");
                           conn.setDoInput(true);
                           if(conn.getResponseCode()==200){
                                   InputStream is=conn.getInputStream();
                                   FileOutputStream fos=new FileOutputStream(file);
                                   byte[] b=new byte[2*1024];
                                   int len=0;
                                   while((len=is.read(b))!=-1){
                                           fos.write(b,0,len);
                                   }
                                   is.close();
                                   fos.close();
                                   return Uri.fromFile(file);
                           }
                   }
                   return null;
           }
           
           
           public static void logI(String msg){
                   Log.i("-------", msg);
           }
   }

   
   
   

AsyncImageTask 

public class AsyncImageTask extends AsyncTask<String, Integer, Uri> {

        private ImageView ivIcon;
        private MyUtil mu;
        private File cache;
        public AsyncImageTask(MyUtil mu,ImageView ivIcon,File cache) {
                this.mu=mu;
                this.ivIcon = ivIcon;
                this.cache=cache;
        }

        @Override
        protected Uri doInBackground(String... arg0) {
                // TODO Auto-generated method stub
                try {
                        return mu.getImageURI(arg0[0], cache);
                } catch (Exception e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                }
                return null;
        }

        @Override
        protected void onPostExecute(Uri result) {
                // TODO Auto-generated method stub
                super.onPostExecute(result);
                if(ivIcon!=null && result!=null){
                        ivIcon.setImageURI(result);
                }
        }
}