Android关于listview中显示网络图片的问题

List<Map<String, Object>> data = new ArrayList<Map<String, Object>>();//初始化，simpleAdapter 需要绑定的数据是List<Map<String,Object>>类型的
                        for (int i = 0; i < bitmap.length; i++) {
                            final Map<String, Object> item = new HashMap<String, Object>();
                            c.setvalue(i);　　　　//因为需要将i变量传递到线程中，就通过一个类的变量进行获取
                            Thread t_ = new Thread(new Runnable() {
                                @Override
                                public void run() {
                                    String url="http://"+StaticValue.add_ip+":8089/images/"+image_url[ c.getvalue()];　　//网络URL
                                    bitmap[c.getvalue()] = getHttpBitmap(url);　　//或获取URL转bitmap的方法
                                    savePicture(bitmap[c.getvalue()],image_url[ c.getvalue()]);//下载到本地
                                }
                            });
                            t_.start();
                            try {
                                t_.join();　　　　//等待线程执行结束
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }

                            FileInputStream fis = null;
                            try {
                                fis = new FileInputStream(Environment.getExternalStorageDirectory().getAbsolutePath()
                                        + "/M2_test/download/" + image_url[i]);　　//获取刚刚子线程中存在本机的图片
                            } catch (FileNotFoundException e) {
                                e.printStackTrace();
                            }
                            BitmapFactory.Options op = new BitmapFactory.Options();
                            op.inPreferredConfig = Bitmap.Config.RGB_565;
                            op.inDither = true;
                            op.inSampleSize = 10;
                            op.inJustDecodeBounds = false;
                            Bitmap bitmap  = BitmapFactory.decodeStream(fis,null,op);

                            item.put("pic", bitmap);
                            item.put("mono", mono[c.getvalue()]);
                            data.add(item);

                        }
　　　　　　　　　　　　　　
　　　　　　　　　　　　　　//simpleAdapter 默认不支持图片的接受，所以需要重写方法
                        SimpleAdapter adapter = new SimpleAdapter(getContext(), data ,R.layout.vlist, new String[]{"pic","mono"}, new int[]{R.id.im ,R.id.tv_mono});
                        adapter.setViewBinder(new SimpleAdapter.ViewBinder() {
                            public boolean setViewValue(View view, Object attentionList, String textRepresentation) {
                                if(view instanceof ImageView && attentionList instanceof Bitmap){
                                    ImageView iv=(ImageView)view;
                                    iv.setImageBitmap((Bitmap) attentionList);
                                    return true;
                                }else{
                                    return false;
                                }
                            }
                        });
                        lv.setAdapter(adapter);

public  Bitmap getHttpBitmap(String url)
    {
        Bitmap bitmap = null;
        try
        {
            URL pictureUrl = new URL(url);
            InputStream in = pictureUrl.openStream();
            bitmap = BitmapFactory.decodeStream(in);
            in.close();

        } catch (MalformedURLException e)
        {
            e.printStackTrace();
        } catch (IOException e)
        {
            e.printStackTrace();
        }

        return bitmap;
    }

    public void savePicture(Bitmap bitmap,String pic_name)
    {
        String pictureName = Environment.getExternalStorageDirectory().getAbsolutePath()
                + "/M2_test/download/" + pic_name;
        File file = new File(pictureName);
        FileOutputStream out;
        try
        {
            out = new FileOutputStream(file);
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, out);
            out.flush();
            out.close();
        } catch (FileNotFoundException e)
        {
            e.printStackTrace();
        } catch (IOException e)
        {
            e.printStackTrace();
        }
    }