listview中的imagestore图像极慢渲染

Question

在我的活动中，我从数据库中读出所有uri，然后我将其传递给listview，但是当我点击“全部显示”按钮时，需要花费很多时间来切换到新活动。这里有一些代码，这是将图片放在listview中的代码。

public MyListAdapter() {
        super(ShowAllActivity.this, R.layout.item_list_view, posts);
    }

    /**
     * Get a view for each post in the list.
     * Uses a default picture if there are no photo. If there is a photo for the post then the photo will be correct rotated.
     */
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        View postView = convertView;
        if (postView == null) {
            postView = getLayoutInflater().inflate(R.layout.item_list_view,
                    parent, false);
        }

        Post currentPost = posts.get(position);
        TextView name = (TextView) postView.findViewById(R.id.tv_item_name);
        TextView title = (TextView) postView
                .findViewById(R.id.tv_item_title);
        TextView date = (TextView) postView.findViewById(R.id.tv_item_date);
        ImageView photo = (ImageView) postView
                .findViewById(R.id.iv_item_photo);
        name.setText(currentPost.getName());
        title.setText(currentPost.getTitle());
        date.setText(currentPost.getDate());

        Uri photoUri = Uri.parse(currentPost.getPhoto());

        Bitmap myBitmap;

        try {

            Uri selectedImage = photoUri;
            String[] filePathColumn = { MediaStore.Images.Media.ORIENTATION };
            Cursor cursor = getContentResolver().query(selectedImage, null,
                    null, null, null);
            cursor.moveToFirst();
            int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
            int rotation = cursor.getInt(columnIndex);
            cursor.close();
            myBitmap = android.provider.MediaStore.Images.Media.getBitmap(
                    getContentResolver(), photoUri);
            Matrix mat = new Matrix();
            mat.postRotate(rotation);
            Bitmap scaledBitmap;
            int scaleFactor = 20;
            scaledBitmap = Bitmap
                    .createScaledBitmap(myBitmap, myBitmap.getWidth()/scaleFactor, myBitmap.getHeight()/scaleFactor, true);
            Bitmap bMapRotate = Bitmap.createBitmap(scaledBitmap, 0, 0,
                    scaledBitmap.getWidth(), scaledBitmap.getHeight(), mat,
                    true);
            photo.setImageBitmap(bMapRotate);
        } catch (FileNotFoundException e) {
            photo.setImageResource(R.drawable.ic_launcher);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            photo.setImageResource(R.drawable.ic_launcher);
        } catch (NullPointerException npe) {
            photo.setImageResource(R.drawable.ic_launcher);
        }
        return postView;
    }
}