Reactive Live Coding during GDG DevFest 2015 in Poland

2015-11-29 Android, Conferences, Google, Java, RxJava 2 comments

I was asked to be a speaker during GDG DevFest 2015 conference in Warsaw, Poland. Of course, I accepted this invitation and prepared presentation titled “Reactive Live Coding”. Presentation covered basics of Reactive Programming, RxJava and RxAndroid. Besides my talk I’ve done live coding to show how to use mentioned libraries and basics principles of Reactive Programming in real life. I had only 20 minutes for all of that, so my time-box was very limited. Being a speaker at conference was really interesting and challenging experience, which I haven’t had before. Moreover, I could meet a lot of interesting people and hear very inspiring talks covering different topics. You can check activity from conference by browsing #devfest15pl hashtag on Twitter and Facebook event. You can also check official website of the conference at

Slides from my presentation are available below.

Source code of the exemplary Android app shown and partially coded during the presentation is available at

Picture documenting part of my short talk made by @depodefi can be found below.


GDG DevFest organizers have done really good job and I can definitely recommend this conference to anyone interested in new IT technologies.

Publishing Android application in Google Play Store

2014-08-31 Android, Google, Play No comments


When you want to publish your Android application in Google Play Store, first you need to go to website and create a Developer account. Its cost is $25. You can read more about that at:

Problems with payments during registration

Remember that you need to have appropriate debit card in order to proceed with payments. E.g. I have debit card in PKO BP (Polish bank), which has two-stage authorization. Most of debit cards has two-stage authorization for the registration of the card in on-line payment system and next payments are verified only once. In my bank every payment is verified twice. It’s more secure, but due to this security policy I was not able to pay for my developer account at all! I decided to create another bank account for on-line payments in bank, which has one-stage authorization for regular payments. I’ve chosen mBank (another Polish bank). Finally, I was able to proceed with payments and create my developer account.

Developer Console

When you have your developer account created, you can access Developer Console with your Google credentials.


When you create your application, you can choose it from the list of available applications and you can manage several sections.


You don’t have to to everything in one session, you can save a “draft” of your application and fill rest of the elements e.g. next day.


Preparing APK file to upload

Before we publish our app in Google Play Store, we need to generate signed *.apk file. In Android Studio, we can choose Generate Signed APK... option from Build menu.


If we don’t have our key store, we need to create one.


Very important: We need to remember or save somewhere our key store password and alias password (they can be the same). We also need to save somewhere (in a few different places) our key store file. Key store file, key store password and alias password are necessary for signing app. If we want to update uploaded app in the future, we need to sign it with exactly the same key store file and we need to know mentioned passwords to perform sign operation. Passwords can be changed, but we need to know old passwords to do it. When we will sign our app with a different key store file, we won’t be able to update our app after uploading.

Next, we need to set master password.


After that, we can click Next and finalize generating *.apk file. In this step, we can optionally run ProGuard.


If everything went ok, we should see the following window.


Now, we are ready to upload our *.apk file to Google Play Store.

Uploading APK file

In APK section you can upload your application compiled into *.apk file to Google Play Store.


You can also set up Beta testing or Alpha testing and distribute your app to selected group of testers.

When, we uploaded our *.apk file, application is marked as “Draft”.


We need to provide all mandatory information in several sections.

When, I filled everything, my application was still a “Draft”. I could display message “Why can’t I publish?” and see details.


I needed to go to “Pricing and Distribution” section and check mandatory fields.


I also needed to mark checkbox Not submitting a privacy policy URL at this time. in “Store Listing” section (“Privacy Policy” subsection).

Store listing

Basic information

In store listing, you need to provide basic information about your app.


Graphic assets – screenshots

Next, you need to provide screenshots of your app. Screenshots for the phone are necessary, but screenshots for the tablets are optional.


Graphic assets – Hi-res icon, promo images & video

Then, you need to provide promo images & video. Two options are mandatory.


Categorization, Contact Details & Privacy Policy

Next, we can categorize our app, set up Contact Details and Privacy Policy if it’s necessary. If we don’t have Privacy Policy, we need to check the field Not submitting a Privacy Policy URL at this time.



We can manage translations and prepare different description, application name, screenshot and other details for different languages. In my case, I prepared description and screenshots in Polish and English language versions.


Pricing & Distribution

In this section you can provide information about distribution. You can determine whether your app will be available all-around the world or only in selected countries. You can also determine if it will be free or paid.


In-app Products

We are able to create in-app products. Application, which I was publishing does not have such feature. You can read more about that at:

Services and APIs

In this section, you can set up Google Cloud Messaging (GCM), Licensing & In-app billing and Google Play Game Services. Here you can get license keys and link your mobile app with server application if it’s neccessary. There is also feature called App Indexing from Google Search, where you can deep link into your app from Google search.

Optimization tips

Here you can see some optimization tips from Google, which you can apply for your app, to make it better.

Launch checklist

Don’t forget to browse Google’s Lauch Checklist.

Ready to publish

After proving all the information, my application was finally ready to publish!


I could click Publish this app button and deploy my application to Google Play Store.
After that, my application was marked as Published on the list of the applications. It’s worth mentioning that applications are not available on Google Play Store immediately after publishing, but within a few hours. I was informed about that after clicking the Publish this app button.


You can see that my app was successfully published. You can download it at:
It’s specific application reading brain waves from NeuroSky MindWave Mobile device, so you need to have such device in order to use this app. It can be connected via Bluetooth to the Android smartphone or tablet.

Last words

Information provided in this article does not cover all functionalities and possibilities of Google Play Store. If you want to learn more, please read official Google’s websites.

First Google Glass Hackathon in Poland

2013-07-30 Glass, Google, Hackathon No comments


Some time ago I participated in first Google Glass Hackathon in Poland, where I had possibility to test Google Glass, try it and write applications, which can be run on this cutting-edge device.
It was very interesting experience. In addition, I took 2nd place with my team, what made me happy after leaving Warsaw late night.
In a few hours, we created simple native application for Android platform, which can be used as a city guide with augmented reality, geolocation and image recognition. We called it Hereandhounds. You can see its source code at:

You can read detailed report from that event at technical blog of Future Processing: Unfortunately, its available only in Polish language right now.

Google I/O 2013

2013-05-15 Conferences, Google No comments


Google I/O 2013 is happening now with live stream! Check this inspiring event at:
Techcrunch is putting new updates about this conference right now, so you can also check googleio2013 tag on their website for more details:

Google shows off Google Glass UI

2013-02-20 Google No comments


On the official Google Glass website we can find how it feels to use it, preview UI and read what it does. Finally, we can also get to know how to get one! It’s a good option for creative individuals, but this cannot be achieved without any effort. Unfortunately, this option is available only for U.S. citizens right now.


This project can be interesting not only for the users, but especially for developers. It could be a great fulfillment for mobile devices and laptops extending everyday technological experience. I don’t know exact details about the platform, programming languages and SDK used in Google Glass, so we have to stay tuned, because this project is becoming more solid and interesting.

Now, we can just take a look at the website of the project:


Promotional movie is also quite nice.


Animate your HTML5!

2013-02-10 Canvas, CSS3, Google, HTML5 No comments


Interesting resource concerning HTML5, CSS3, Canvas, graphics & animation inside the web browser:

Don’t forget to check out the presentation!

Redesigning Google

2013-01-24 Design, Google No comments

Redesigning Google

How Larry Page engineered a beautiful revolution? Article by The Verge.

Redesigning Google