Saturday, 10 December 2016

How to take a screenshot on your Chromebook


Your Chromebook is different from your personal laptops and Desktops. There are two essential things to consider before you go for a chromebook
  1. Chrome OS : This is the OS that runs on your chromebook. You need to get familiar with it. Chrome OS is an operating system designed by Google and based upon the Linux kernel. Google announced the project in July 2009, conceiving it as an operating system in which both applications and user data reside in the cloud: hence Chrome OS primarily runs web applications. (Wiki)
  2. Cloud computing : This is a major deal breaker here. Chromebook essentially is a cloud computing device. You access your data stored in cloud and signout when done.
Without these two your chromebook is essentially a browser!

There are tons of different things associated with chromebook from it's keyboard layout, its file directories all the way to the apps you run on it. Will get into those details in perhaps upcoming posts but in this post we will see how to take a screenshot on your chromebook.

How to take a screenshot on your Chromebook

  • To take screenshot of entire screen you need to press ‘Ctrl’ and ‘Window Switcher’ keys together.

  • To get a part of the screen you need to press ‘Ctrl’ , ‘Shift’  and ‘Window Switcher’ keys together.

Once you do that you should see a notification saying "Screenshot taken".

Screenshots will be available under Downloads directory of your chromebook.

 As I mentioned earlier keyboard layout of your chromebook is different than your traditional laptop. For eg. you don't have a capslock or a delete button. Instead if capslock you would see a search button. Anyway to understand keyboard shortcuts you can press
  • Ctrl + Alt + ?
And you should see a keyboard layout. When you press on
  • Ctrl or
  • Search or
  • alt or
  • their combinations
you should see their corresponding key shortcuts. For rg when you press Ctrl while on that layout you can see all shortcuts starting with Ctrl. Notice the screenshot shortcut we saw above -

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Sunday, 27 November 2016

How to Uninstall Apps from Android Wear


In last post we had some discussion on how to add a wearable module to your existing android app. In this post we will see how to uninstall app from your your android wear. For this you need to have Android wear app installed on your phone -
 Lets see now how we can remove the app.

How to Uninstall Apps from Android Wear

  • Make sure you are connected to your wearable device from your wearable app installed on your phone

  • Next click on settings icon.

  • Under Device Setting click on your device connected

  • Next click on watch storage and you should see your app listed there.

  • You cannot directly uninstall app from here. Rather you cannot uninstall app from wear device and still keep it on your mobile (Unless you use adb command to remove it :)). Anyway uninstall the app from your device. Go to your connected app and click on Resync apps. Your app on wearable device should automatically get removed.

Related Links

Adding and packaging wear module to your existing Android application


Smart watches are slowing making their way into the market. They are quite expensive today but hoping prices will slash down with increase of technology. Anyway this post is aimed to add a wearable module to your existing Android app. This post expects you
  1. Have an existing Android application code
  2. Have it setup in latest Android Studio
So now that we have our prerequisites in place lets see how we can do this.

Step 1 : Adding a wearable  module to your Android application

If you have have your android application code opened in studio you simply need to 
  1. Open module settings
  2. Create on + (plus) button and select "Android Wear Module" .
  3. Next give your module name (NOTE : Make sure your wear module bundle id is same as your main android app bundle id)
  4. Next select activity
  5. Give your activity/layout name
  6. Click Finish

 Once you do this you should see a new module in your project with the name you provided during configuration. It will have its own set of java files, resource files, icons, manifest, build.gradle file etc.

You can go ahead and code your logic into this. This will run on your wearable device.

Step 2 : Packaging Wearable Apps

The way wearable app is distributed is by packaging it inside your handheld application (apk gets bundled inside) and when this app is installed on your phone/handheld device the wearable apk will get pushed to your wearable device.

To properly package a wearable module -
  1. Include all the permissions declared in the manifest file of the wearable app module in the manifest file of the handheld app module. For example, if you specify the VIBRATE permission for the wearable app, you must also add that permission to the handheld app.
  2. Ensure that both the wearable and handheld app modules have the same package name and version number.
  3. Declare a Gradle dependency in the handheld app's build.gradle file that points to the wearable app module: 


    dependencies {
        compile fileTree(dir: 'libs', include: ['*.jar'])
        testCompile 'junit:junit:4.12'
        compile ''
        compile ''
        compile ''
        wearApp project(':flashlightwear')

  4. Click Build > Generate Signed APK.

How it works

  • Your android mobile/handheld application and your wearable application (apk) should be signed using same certificate (key). 
  • They must also have same package name and version number.
  • When you generate a release build if your handheld application your wearable apk will get bundled in your handheld apk.
  • When you install your handheld app on your mobile which is paired to your wearable device (eg smart watch) then wearable apk bundled within will be automatically pushed and installed on the wearable device.
  • You cannot take a call on which ones to keep or not keep. If you have an app installed on your mobile device and it has a wear module it will be installed on your wearable device. You cannot uninstall it unless you remove the app from your phone.

You should see a notification on your wear device that app is installed.

I have added wear module to a flashlight app that I had developer sometime back just to learn this stuff. You can check it out. Its available on playstore -

  1. Ensure that both the wearable and handheld app modules have the same package name and version number.
  2. Include all the permissions declared in the manifest file of the wearable app module in the manifest file of the handheld app module. 
  3.  Your android mobile/handheld application and your wearable application (apk) should be signed using same certificate (key).
  4. wearable apk gets automatically bundled with your handheld module and gets pushed to your wearable device once installed on handled device.

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Saturday, 26 November 2016

Setting up Firebase Cloud Messaging (FCM) in Android application


In last post we say what FCM was and how is it better then the old GCM notifications. 
 Last post was mainly about your server configuration to send FCM notification to a single device. But that assumed that your device is already registered to FCM server and your server has that ID. In this post we will see how to create, register and setup FCM on your Android device. This can be your smart phone or your smart watch app.

Getting started with Firebase Cloud Messaging (FCM)

First of all you need to log into Firebase console -
Log in. Signup if you already don't own a account. Once done you will need to create a new project.

 Once you do that you should see following page.

 As mentioned in previous post as FCM is cross platform you can see Android/iOS/Web. We will concentrate on Android for now. So go ahead and select it. Post clicking it you have 3 steps to perform

  1. provide your android bundle iD
  2. Download google-service.json file and put it under your app folder of Android project
  3. Add dependency to classpath

In app level build.gradle add the firebase dependency you need. For eg in this case we need cloud messaging for FCM. So you can add

compile ''

You can see all available dependencies here -

under Available libraries section. It looks like below -

Once that is setup your configuration is more or less done. You now also see the server API id we used in previous post from  this project that you have just created. Anyway lets move on the code changes we need.

Code changes needed

Add following services in your manifest file of android module -
        <service android:name="">
                <action android:name="" />
        <service android:name="">
                <action android:name="" />

These services are basically the ones which generate token (registration id we need while sending FCM from server) and receiving message from server. Code for them goes as follows -


 * Created by athakur on 11/25/16.
public class MyFirebaseMessagingService extends FirebaseMessagingService {

    private static final String loggerName = MyFirebaseMessagingService.class.getSimpleName();

    public void onMessageReceived(RemoteMessage remoteMessage) {

        Log.d(loggerName,"From: " + remoteMessage.getFrom());

        // Check if message contains a data payload.
        if (remoteMessage.getData() != null) {
            Log.d(loggerName, "Message data payload: " + remoteMessage.getData());

            String title = remoteMessage.getData().get("messageTitle");
            String body = remoteMessage.getData().get("messageBody");

            if(StringUtils.hasText(title) && StringUtils.hasText(body))
                Log.d(loggerName, "Showing notification for message");
                showNotification(title, body,this);


        // Check if message contains a notification payload.
        if (remoteMessage.getNotification() != null) {
            Log.d(loggerName, "Message Notification Body: " + remoteMessage.getNotification().getBody());

MyFirebaseMessagingService class will get the  payload send by server during FCM notification. Your payload can have data or notification payload. Notification payload is directly shown as notification on android device where as data payload needs to be handle by your client application


 * Created by athakur on 11/25/16.
public class MyFirebaseInstanceIDService extends FirebaseInstanceIdService {

    private static final String loggerName = MyFirebaseInstanceIDService.class.getSimpleName();

    public void onTokenRefresh() {
        // Get updated InstanceID token.
        String refreshedToken = FirebaseInstanceId.getInstance().getToken();
        Log.d(loggerName, "FCM token refreshed: " + refreshedToken);

        // If you want to send messages to this application instance or
        // manage this apps subscriptions on the server side, send the

    private void sendFcmTokenToServer(String token) {
        Log.d(loggerName, "Sending FCM refresh token to server");

And you should be done.  MyFirebaseInstanceIDService class will give you a callback when token is refreshed , you need to update it on your server. Once that is done your server will be able to send FCM notifications to you (exactly what we saw in last post).

Once you do this on your app start these service should automatically start. You will get token in callback and message in other callback of respective services that we have implemented. You can take actions appropriately. Sync data or show notification etc.


I have already implemented this in a demo android app that you can refer to. Link to github project -

Related Links

Friday, 25 November 2016

How to send Firebase Cloud Messaging (FCM) notification from server to client


Firebase Cloud Messaging (FCM) is a cross-platform messaging solution that lets you reliably deliver messages at no cost. It is an improved version of Google Cloud Messaging (GCM). Following are some of the features that makes FCM stand out -
  1. It is cross platform so it is a natural fir for all.
  2. Using FCM you can send two types of payloads to the client
    1. Notification type in which case a notification will be directly shown on the client
    2. Data payload in which case client has to parse and act on it
  3. You can distribute message to your client app in one of the following 3 ways -
    1. Send it to a single device
    2. Send it to a group of devices
    3. Send it to devices subscribed to topics
  4. Lastly you can also send messages from client back to the server.

 I am not going to bore you with any more details here. This post is simply meant to explain server side implementation of how to deliver FCM messages to client. We will see client setup in future posts.

To view how to setup firebase project and set up a client refer -

Following in Java code to send FCM message to a single device -

import java.util.HashMap;


import org.apache.http.HttpStatus;
import org.json.JSONException;
import org.json.JSONObject;

 * @author athakur
public class FCMMessageSender {
    public static final String FCM_URL = "";
    public static final String FCM_SERVER_API_KEY    = "<ADD_YOUR_SERVER_API_KEY>";
    private static final String deviceRegistrationId =  "<ADD_YOUR_DEVICE_REG_ID>";

    public static void main(String args[])
        int responseCode = -1;
        String responseBody = null;
            System.out.println("Sending FCM request");
            byte[] postData = getPostData(deviceRegistrationId);
            URL url = new URL(FCM_URL);
            HttpsURLConnection httpURLConnection = (HttpsURLConnection)url.openConnection();

            //set timeputs to 10 seconds

            httpURLConnection.setRequestProperty("Content-Type", "application/json");
            httpURLConnection.setRequestProperty("Content-Length", Integer.toString(postData.length));
            httpURLConnection.setRequestProperty("Authorization", "key="+FCM_SERVER_API_KEY);


            OutputStream out = httpURLConnection.getOutputStream();
            responseCode = httpURLConnection.getResponseCode();
            if (responseCode == HttpStatus.SC_OK)
                responseBody = convertStreamToString(httpURLConnection.getInputStream());
                System.out.println("FCM message sent : " + responseBody);
                responseBody = convertStreamToString(httpURLConnection.getErrorStream());
                System.out.println("Sending FCM request failed for regId: " + deviceRegistrationId + " response: " + responseBody);
        catch (IOException ioe)
            System.out.println("IO Exception in sending FCM request. regId: " + deviceRegistrationId);
        catch (Exception e)
            System.out.println("Unknown exception in sending FCM request. regId: " + deviceRegistrationId);
    public static byte[] getPostData(String registrationId) throws JSONException {
        HashMap<String, String> dataMap = new HashMap<>();
        JSONObject payloadObject = new JSONObject();

        dataMap.put("name", "Aniket!");
        dataMap.put("country", "India");
        JSONObject data = new JSONObject(dataMap);;
        payloadObject.put("data", data);
        payloadObject.put("to", registrationId);

        return payloadObject.toString().getBytes();
    public static String convertStreamToString (InputStream inStream) throws Exception
        InputStreamReader inputStream = new InputStreamReader(inStream);
        BufferedReader bReader = new BufferedReader(inputStream);

        StringBuilder sb = new StringBuilder();
        String line = null;
        while((line = bReader.readLine()) != null)

        return sb.toString();


Output :
Sending FCM request
FCM message sent : {"multicast_id":8122119840448534941,"success":1,"failure":0,"canonical_ids":0,"results":[{"message_id":"0:1480094913845339%a8fa321bf9fd7ecd"}]}

You can read about various payloads you can send to various devices/device groups/devices subscribed to topics in following link -
 As for the server api key you can get it from your project in Firebase console under Setting -> Cloud messaging.


  • Firebase Cloud Messaging (FCM) is the new version of GCM. It inherits the reliable and scalable GCM infrastructure, plus new features! See the FAQ to learn more. If you are integrating messaging in a new app, start with FCM. GCM users are strongly recommended to upgrade to FCM, in order to benefit from new FCM features today and in the future.  
  • When I refer to client it can be an android app or Android wear (yes it is supported from Android Wear 2.0 Developer Preview)
  • For Json library I am using - <dependency org="org.json" name="json" rev="20160810"/> [Ivy dependnecy]

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