Android Volley似乎没有发布HTTP参数

我在StackOverflow上看到了一些这样的问题,但我似乎无法弄清楚为什么这段代码对我不起作用.

public void postMethod(final String msg) {

    String url = "http://192.168.1.30/endpoint";

    RequestQueue queue = Volley.newRequestQueue(this);
    StringRequest sr = new StringRequest(Request.Method.POST, url, 
        new Response.Listener<String>() {

        @Override
        public void onResponse(String response) {
            // Handle response...
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            // Handle error...
        }
    }){
        @Override
        protected Map<String,String> getParams(){
            Map<String,String> params = new HashMap<String, String>();
            params.put("msg", msg);

            return params;
        }

        @Override
        public Map<String, String> getHeaders() throws AuthFailureError {
            Map<String,String> params = new HashMap<String, String>();
            params.put("Content-Type","application/x-www-form-urlencoded");
            return params;
        }
    };
    queue.add(sr);
}

我正在尝试对运行python flask应用程序的服务器发出POST.如果我使用程序来发出HTTP Post请求我的服务器应用程序工作正常.如果我使用AsyncTask并且做了Volley试图为我做的事情,它也会正常工作.

从我看到的所有示例中,此代码应该可以正常工作,但我的烧瓶服务器永远不会收到任何POST参数.有什么想法可能会发生什么？

编辑

服务器代码：

from flask import Flask, request, abort
app = Flask(__name__)

@app.route('/endpoint', methods=['POST'])
def echo_msg():
    if request.method == 'POST':
        try:
            msg = request.form['msg']
            return msg

        except KeyError, e:
            # A required parameter is missing.
            abort(400)

你需要覆盖getBodyContentType()并返回“application / x-www-form-urlencoded; charset = UTF-8”;

StringRequest jsonObjRequest = new StringRequest(Request.Method.POST,
            getResources().getString(R.string.base_url),
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {

                    MyFunctions.toastShort(LoginActivity.this, response);
                }
            }, new Response.ErrorListener() {

                @Override
                public void onErrorResponse(VolleyError error) {
                    VolleyLog.d("volley", "Error: " + error.getMessage());
                    error.printStackTrace();
                    MyFunctions.croutonAlert(LoginActivity.this,
                            MyFunctions.parseVolleyError(error));
                    loading.setVisibility(View.GONE);
                }
            }) {

        @Override
        public String getBodyContentType() {
            return "application/x-www-form-urlencoded; charset=UTF-8";
        }

        @Override
        protected Map<String, String> getParams() throws AuthFailureError {
            Map<String, String> params = new HashMap<String, String>();
            params.put("username", etUname.getText().toString().trim());
            params.put("password", etPass.getText().toString().trim());
            return params;
        }

    };

    AppController.getInstance().addToRequestQueue(jsonObjRequest);