Author: Smin Rana

This could happen if you have two entries like in your AndroidManifest.xml. If you choose File -> New -> Activity -> Blank Activity this gets included in manifest file automatically. If you are not building for wearable you can delete this from manifest file or add missing library in build.gradle (app)

<uses-library
    android:name="com.google.android.wearable"
    android:required="true" />
<!--
       Set to true if your app is Standalone, that is, it does not require the handheld
       app to run.
-->
<meta-data
    android:name="com.google.android.wearable.standalone"
    android:value="true" />

This could also happen when your app expecting a library which is not installed yet. Please update your build.gradle for any missing library.

Volley is an HTTP library that makes networking for Android apps easier and most importantly, faster. Volley is available on GitHub.

Find your build.gradle (app) add this under dependencies

implementation 'com.android.volley:volley:1.2.0'

Create a singleton class to manage all requests

import android.content.Context;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.Volley;

public class AppHttp {
    private static AppHttp instance;
    private RequestQueue requestQueue;
    private static Context ctx;

    private AppHttp(Context context) {
        ctx = context;
        requestQueue = getRequestQueue();
    }

    public static synchronized AppHttp getInstance(Context context) {
        if (instance == null) {
            instance = new AppHttp(context);
        }
        return instance;
    }

    public RequestQueue getRequestQueue() {
        if (requestQueue == null) {
            // getApplicationContext() is key, it keeps you from leaking the
            // Activity or BroadcastReceiver if someone passes one in.
            requestQueue = Volley.newRequestQueue(ctx.getApplicationContext());
        }
        return requestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req) {
        getRequestQueue().add(req);
    }
}

Create your POST request

AppHttp requestQueue = AppHttp.getInstance(this);
JSONObject postData = new JSONObject();
    try {
        postData.put("email", email);
        postData.put("password", password);

    } catch (JSONException e) {
        e.printStackTrace();
    }

    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.POST, "http://api.com/login", postData, new Response.Listener<JSONObject>() {

        @Override
        public void onResponse(JSONObject response) {
            Log.e("login response: ", response.toString());
            try {
                // Retrieve user information and take user to next activity
               // after successful login
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    },
        new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.e("login error: ", error.toString());
                error.printStackTrace();

                // show user login error with a Toast
            }
        }
    ) {
        @Override
        public Map<String, String> getHeaders() throws AuthFailureError {
            Map<String, String> params = new HashMap<>();
            params.put("Accept", "application/json;charset=utf-8");
            params.put("Content-Type", "application/json;charset=utf-8");

            return params;
        }
    };

    requestQueue.addToRequestQueue(jsonObjectRequest);
}