如何使我的代码成为同步 POST volley 请求？

Question

I'm building a tracking app for exercise. As the gps updates every 1 second, the latitude and longitude is added to an array. At the end of the exercise, when you press save, below method is executed, sending all co-ordinates to a database. Because it's an asynchronous request, the co-ordinates don't get loaded into the database in correct order. How can I fix this so it will wait until each iteration of loop is complete or something like that. Thanks

/* Inserts the latitude and longitude points from the latitudeAndLongitudePoints ArrayList into the latitudeandlongitudepoints table in db*/

private void insertLatitudeAndLongitudePoints(){

    //iterates though array of co-ordinates, and adds to database
    for(int loop=0; loop<latitudeAndLongitudePoints.size();loop++) {

        final int index = loop;

        StringRequest stringRequest = new StringRequest(Request.Method.POST,
                "http://rrush01.lampt.eeecs.qub.ac.uk/insertLatitudeAndLongitudePoints.php",
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Toast.makeText(getApplicationContext(), "Error: " + error.getMessage(), Toast.LENGTH_LONG).show();
            }
        }) {
            @Override
            protected Map<String, String> getParams() throws AuthFailureError {
                Map<String, String> params = new HashMap<>();

                params.put("Latitude", String.valueOf(latitudeAndLongitudePoints.get(index).latitude));
                params.put("Longitude", String.valueOf(latitudeAndLongitudePoints.get(index).longitude));
                params.put("User", AccountInfo.accountEmail);

                return params;
            }
        };

        RequestQueue queue = Volley.newRequestQueue(this);
        queue.add(stringRequest);
    }
}

Answer 1

Add dependency for Volley library in your build.gradle.

compile 'com.android.volley:volley:1.0.0'

Volley is a network library which makes fast and easier to make HTTP Request for android application. Using Volley library we don't need to create AsyncTask to make multiple API calls in volley there is RequestQueue where we can enqueue each request. Here in this example, We used Google place autocomplete API. We are going to make synchronous HTTP Request using volley. To make synchronous HTTP request make a RequestFuture object. And make JsonObjectRequest pass this parameter RequestMethod, URL, pass object of type Json and pass RequestFuture instance.

    RequestFuture<JSONObject> requestFuture=RequestFuture.newFuture();
    final String mURL = "https://maps.googleapis.com/maps/api/place/
    autocomplete/json?key="+KEY+"&input=" + input;
    JsonObjectRequest request = new JsonObjectRequest(Request.Method.POST,
    mURL,new JSONObject(),requestFuture,requestFuture);
    MySingleton.getInstance(mContext).addToRequestQueue(request);

Add your request in RequestQueue. Now, whenever the user makes an HTTP request each request added to RequestQueue.To get response object from the requestFuture we call get() method. And we also set a timeout of let's say 10 seconds so we don't block the UI thread indefinitely in case our request times out.

try {
        JSONObject object= requestFuture.get(10,TimeUnit.SECONDS);
    } catch (InterruptedException e|ExecutionException e|TimeoutException e) {
        e.printStackTrace();
    }

Hope this helps you to understand how we can use volley used to make the synchronous HTTP request