Android多部分请求

Question

我正在使用Volley lib，我想用字符串参数发出一个多部分请求

我找到了这段代码

/**
 * MultipartRequest - To handle the large file uploads.
 * Extended from JSONRequest. You might want to change to StringRequest based on your response type.
 * @author Mani Selvaraj
 *
 */
public class MultiPartRequest extends JsonRequest<JSONObject> {

    /* To hold the parameter name and the File to upload */
    private Map<String,File> fileUploads = new HashMap<String,File>();

    /* To hold the parameter name and the string content to upload */
    private Map<String,String> stringUploads = new HashMap<String,String>();

    private Map<String, String> headers = new HashMap<String, String>();

    /**
     * Creates a new request.
     * @param method the HTTP method to use
     * @param url URL to fetch the JSON from
     * @param jsonRequest A {@link JSONObject} to post with the request. Null is allowed and
     *   indicates no parameters will be posted along with request.
     * @param listener Listener to receive the JSON response
     * @param errorListener Error listener, or null to ignore errors.
     */
    public MultiPartRequest(int method, String url, JSONObject jsonRequest,
                            Response.Listener<JSONObject> listener, Response.ErrorListener errorListener) {
        super(method, url, (jsonRequest == null) ? null : jsonRequest.toString(), listener,
                errorListener);
    }

    /**
     * Constructor which defaults to <code>GET</code> if <code>jsonRequest</code> is
     * <code>null</code>, <code>POST</code> otherwise.
     *
     * @see #JsonObjectRequest(int, String, JSONObject, Listener, ErrorListener)
     */
    public MultiPartRequest(String url, JSONObject jsonRequest, Response.Listener<JSONObject> listener,
                            Response.ErrorListener errorListener) {
        this(jsonRequest == null ? Method.GET : Method.POST, url, jsonRequest,
                listener, errorListener);
    }


    public void addFileUpload(String param,File file) {
        fileUploads.put(param,file);
    }

    public void addStringUpload(String param,String content) {
        stringUploads.put(param,content);
    }

    public Map<String,File> getFileUploads() {
        return fileUploads;
    }

    public Map<String,String> getStringUploads() {
        return stringUploads;
    }

    @Override
    public Map<String, String> getHeaders() throws AuthFailureError {
        return headers;
    }

    public void setHeader(String title, String content) {
        headers.put(title, content);
    }

    @Override
    protected Response<JSONObject> parseNetworkResponse(NetworkResponse response) {
        try {
            String jsonString =
                    new String(response.data, HttpHeaderParser.parseCharset(response.headers));
            return Response.success(new JSONObject(jsonString),
                    HttpHeaderParser.parseCacheHeaders(response));
        } catch (UnsupportedEncodingException e) {
            return Response.error(new ParseError(e));
        } catch (JSONException je) {
            return Response.error(new ParseError(je));
        }
    }
}

这是一种正确的方法吗？

RequestQueue queue = MyVolley.getRequestQueue();
        MultiPartRequest multiPartRequest = new MultiPartRequest(url,null,new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(JSONObject response) {

            }
        },new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {

            }
        });
        multiPartRequest.addFileUpload("logo",file);
        multiPartRequest.addStringUpload("firsName","John");
        queue.add(multiPartRequest);

但有一点我无法理解如何使用此代码发送文件和其他参数。

正如类JsonReqest中提到的那样，post params可以为null。但我无法理解我怎么能用它。请有人能告诉我怎么能这样做？