Full project with source code to create a Singleton class for our Volley RequestQueue, so we can use the same RequestQueue instance throughout the whole lifetime of our app, instead of just creating it with the context of a single activity. This is the recommended approach if your app makes constant use of network requests
dependencies
dependencies {
...
implementation 'com.android.volley:volley:1.2.1'
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="16dp"
tools:context="tech.codingpoint.volleysingletonexample.MainActivity">
<TextView
android:id="@+id/text_view_result"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="@android:color/black"
android:textSize="20sp" />
<Button
android:id="@+id/button_parse"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="29dp"
android:text="parse" />
</RelativeLayout>
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="tech.codingpoint.volleysingletonexample">
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
MainActivity.java
package tech.codingpoint.volleysingletonexample;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
public class MainActivity extends AppCompatActivity {
private TextView mTextViewResult;
private RequestQueue mQueue;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTextViewResult = findViewById(R.id.text_view_result);
Button buttonParse = findViewById(R.id.button_parse);
mQueue = VolleySingleton.getInstance(this).getRequestQueue();
buttonParse.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
jsonParse();
}
});
}
private void jsonParse() {
String url = "https://api.myjson.com/bins/kp9wz";
JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null,
new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
try {
JSONArray jsonArray = response.getJSONArray("employees");
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject employee = jsonArray.getJSONObject(i);
String firstName = employee.getString("firstname");
int age = employee.getInt("age");
String mail = employee.getString("mail");
mTextViewResult.append(firstName + ", " + String.valueOf(age) + ", " + mail + "\n\n");
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
error.printStackTrace();
}
});
mQueue.add(request);
}
}
VolleySingleton.java
package tech.codingpoint.volleysingletonexample;
import android.content.Context;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.Volley;
public class VolleySingleton {
private static VolleySingleton mInstance;
private RequestQueue mRequestQueue;
private VolleySingleton(Context context) {
mRequestQueue = Volley.newRequestQueue(context.getApplicationContext());
}
public static synchronized VolleySingleton getInstance(Context context) {
if (mInstance == null) {
mInstance = new VolleySingleton(context);
}
return mInstance;
}
public RequestQueue getRequestQueue() {
return mRequestQueue;
}
}