android加载本地目录下的所有图片，使用listview展示

/**文件夹下所有图片的bitmap*/
    private List<Bitmap> listpath;
    /**文件夹下图片的真实路径*/
    private String scanpath;
    /**显示图片的适配器*/
    private Photodaapter adapter;
    /**所有图片的名字*/
    public String[] allFiles;
    /**想要查找的文件夹*/
    private File folder;

listpath = new ArrayList<>();
        folder = new File(Environment.getExternalStorageDirectory().getAbsolutePath().toString() + "/OnePieceSD/FloorPage/");//图片地址
        /**将文件夹下所有文件名存入数组*/
        allFiles = folder.list();
        if (allFiles.length<1){
            Toast.makeText(TerrainActivity.this,"暂无图片",Toast.LENGTH_LONG).show();
        }else {
            /**遍历数组*/
            for (int i = 0; i < allFiles.length; i++) {
                scanpath = folder + "/" + allFiles[i];
                Log.i(TAG, "initData: "+scanpath);
                /**将文件转为bitmap如果为空则不是图片文件*/
                Bitmap bitmap = BitmapFactory.decodeFile(scanpath);
                if(bitmap!=null) {
                    listpath.add(bitmap);
                }
            }
            /** 图片写入适配器*/
            adapter = new Photodaapter(listpath, this);
            terrainList.setAdapter(adapter);
        }


public class Photodaapter extends BaseAdapter {
        private List<Bitmap> mlist;
        private LayoutInflater minflater;

        public Photodaapter(List<Bitmap> list, Context context) {
            super();
            this.mlist = list;
            this.minflater = LayoutInflater.from(context);
        }

        @Override
        public int getCount() {
            return mlist.size();
        }

        @Override
        public Object getItem(int position) {
            return mlist.get(position);
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(final int position, View convertView, final ViewGroup parent) {
            VIewHolder viewholder;
            if (convertView == null) {
                viewholder = new VIewHolder();
                convertView = minflater.inflate(R.layout.terr_img_item, null);
                viewholder.img_item = (ImageView) convertView.findViewById(R.id.img_item);
                convertView.setTag(viewholder);
            } else {
                viewholder = (VIewHolder) convertView.getTag();
            }
            viewholder.img_item.setImageBitmap(mlist.get(position));
            return convertView;
        }
        class VIewHolder {
            ImageView img_item;
        }
    }