5 notes on MVP architecture pattern for Android

                                                           Image credits Macoscope

MVP (Model View and Presenter) is an architectural pattern inspired by the popular MVC pattern.

MVP addresses two main points :

  1. Make views as dumb as possible. The dumber the better.
  2. Make each layer loosely coupled and easily testable in isolation.

I am using MVP in one of my production project and have used in some dem0 apps. Here are my 5 notes on using MVP for android.

  1. Package Structure :

Android project contains lots of code and files even for application of medium complexity. Even when not following MVP I have found that arranging the project files in such a way that files that are accessed together are put in same package is more efficient and intuitive than any other approach.

What I prefer doing is create separate package for separate verticals of the app and put all related files like activities, fragments, views, presenters, adapters etc in that package.

ex. packages like add task, view task, list task for a To-Do app.

2. Libraries that are useful for MVP :

In MVP you want your model and presenter to be independent of the life cycle of view. For this, you can use dependency injector library like Dagger2.

Other than that, using RxJava and reactive programming principles for creating presenter is also becoming increasingly popular.

Libraries you can use for this purpose are : RxAndroid and EventBus.

3. Managing Remote and local data sources in the Model :

Android apps have to fetch data from the server. At the same time fetched data must be cached to make the app usable offline and increase the speed.

What I prefer doing is to create three model classes :

1. Remote Data Source

2. Local Data Source

3. Data Repository

All presenters talk to Data Repository class. Data repository model contains references to Local and Remote data repository and calls data from either according to situation.

As the name suggests Local Data Source deals with cached data and disk storage whereas Remote Data Source deals with API calls and responses.

4. User Experience is the top priority :

One thing that we all have to keep in mind that the real test of application is, if it is able to provide user a nice experience.

At the end of the day, user only notices the user experience of the application and not the architecture used. So if you have to make some design sacrifices to make the UX better, do it.

The real test of the machine is the satisfaction it provides to the mind. There is no other bigger test.

5. Testing Advantages :

Main motive behind MVP pattern was to make the testing of layers easy.

Basic idea is to keep the presenter and model android free, so that they can be tested without Android instrumentation by the JVM itself.

Views can then be tested by Android Instrumentation tests.

Mockito and Espresso can come handy for testing purposes.

Conclusion :

MVP, in my opinion is so far the best way to architect your android application project. It simplifies many issues like testing and making views lighter. Combine it it RxJava and dependency injection and you’ve got a nice recipe for android projects.

I am learning more about RxJava and testing frameworks will share my views on that soon.

Thanks.

Practice Shapes : Android App To Learn Shapes

Only way to learn something is to learn it by yourself.

Recently I have been playing with Canvas in android and it has been fun! 😀

As they say knowledge is knowing tomato is a fruit. Wisdom is not putting it in vegetable basket. And best way to persist new gained “wisdom” is to put it in use.

Practice Shapes is a fun app both for kids and grown-up kids (Yes. You!), to test their drawing skills. Though I know drawing on a mobile screen with your fingers is not your favorite thing, but still you will enjoy it! 😀

Download the app from play store :

 

This app is open source : You can fork it at https://github.com/priyankvex/Practice-Shapes/

 

TECH STACK : 

  • Android SDK
  • Bitmap Images of Shapes

The power lies in not reinventing the wheel, but to use it to move forward.

OPEN SOURCE LIBRARIES USED : 

  1. Universal Image Loader
  2. Sugar ORM
  3. Fancy Buttons

To Create Images : 

To create images for the app on which user draws, i used GIMP. These are just simple images with transparent background.

Right now, there are total of 18 images in the app under 3 difficulty levels.

If you can add more images feel free to do so.

Screenshots of app : 

drawing_ss

hard_shapes_ssscore

Download the app from play store :


Rails Number Helper Port to Android

A polyglot developer will understand, there is always something you like about one language and you wish was available for another language too.

So, recently I started learning rails and found number_helper API very cool and fun to use. It gives you easy API to convert numbers into many formats like number_to_human which will convert 20000 to 20 Thousands or number_to_human_size that will convert 1024 to 1 KB.

That was it I wanted this stuff for Android too. It just makes processing numbers to fit the UI needs so damn easy.

Here is my attempt to port this rails module to Android.

Here is the source code :

https://github.com/priyankvex/Rails-Number-Helper-For-Android

Usage : 

Just copy the module number_helper in your application folder and include module dependency.

Examples : 

 


        // Number to human converter
        NumberToHumanConverterBuilder builder2 = new NumberToHumanConverterBuilder(123456);
        NumberToHumanConverter converter2 = builder2.build();
        try {
            String humanNumber = converter2.convert();
            // OUTPUT : 123.456 Thousands
            Log.d(Config.TAG, humanNumber);
        } catch (InvalidSeparatorException | InvalidDelimiterException
                | InvalidPrecisionException e) {
            e.printStackTrace();
        }

Examples can be found here.
https://github.com/priyankvex/Rails-Number-Helper-For-Android/blob/master/app/src/main/java/com/wordpress/priyankvex/numberhelperdemo/MainActivity.java

Features : 

  • Easy to use API.
  • High utility for UI needs.
  • Small in size.
  • Custom exceptions to fit the needs of Android.

 

Making GCM client in Android and Application server in Ruby on Rails

It is always fun to play with new APIs and tools. GCM is not something I was getting my hands on for the first time but it changed completely since last time I did a project using this.

But the good news is it has changed for good. New service classes makes it easier to write GCM clients for Android, GCM default configuration makes writing test servers and apps to play with very less tedious. In fact my first reaction was this is GCM reincarnated. 

GCM Client and App server
GCM Client and App server

New API : New Party!

You can have a look at the source code here :

https://github.com/priyankvex/GCM-Android-Client-and-Rails-Server

To create Android client I stuck with sample provided in the docs. Sweet and simple to implement. Just little tweaks done to make it fit my needs.

For creating application server i.e the 3rd party server required by the GCM stack, it used Ruby on Rails. In that specifically I used “gcm” gem.

Again not a very complex server but good enough to get a hold of things.

Server features : 

  1. Save incoming device tokens (registration ids).
  2. Web form to send message to all devices registered.
  3. Send welcome notification when device is registered.

Client features (Android App) :

  1. Get GCM token for the device.
  2. Send token to applications server.
  3. Show notification when message is pushed from server.

 

Paint App in Android

Recently I was learning about Canvas and Custom views in Android and to put the theory in practice I made a pretty simple Paint App. 

Source code of the app can be found https://github.com/priyankvex/Paint-App-Android.

Screenshot of the app
Screenshot of the app

 

The App is pretty simple with features
1.  Create Drawings (Obvious one :P).
2.  Select different brush sizes.
3.  Eraser with different sizes.
4.  Color pallet.
5.  Save drawings in Gallery.

Source code of the app can be found https://github.com/priyankvex/Paint-App-Android.

Brownie points if you can guess the character I drew! 😀

Making an OCR app for Android using Tesseract.


Star on GitHub

Recently I was playing with OCR library by google called as “Tesseract” (cool name for a library!).

App in action.
App in action.

 

Screenshot_2015-08-29-23-08-51

 

 

 

 

 

 

 

 

It was a fun experience. This post shows how you can make a simple OCR app in Android using Tesseract.

We will be using Tess-Two a fork of Tesseract with some additional tools like Liptonica which is an image processing library.

If you want an even easier way to get started with OCR on Android you can try this library built by me. Easy OCR Library. Usage instructions are in the ReadMe.md file there.

Anyways, moving forward I am using Android Studio on Ubuntu 64 bit machine here.

Step 1 : 

Clone the library Tess-Two.


git clone git://github.com/rmtheis/tess-two tess

Step 2 :

Now we need to build  the library.

For building we will need Android NDK.


cd tess
cd tess-two
ndk-build
android update project --path .
ant release

Building may take some time so be patient. Don’t press ctrl+c too soon 😛 .

Step 3  :

Yay! Time to use the library in Android Project.

Copy the tess/tess-two folder into the root folder of your application project.

Step 4 : 

In the tess-two folder you just pasted. Add build.gradle file as Android Studio uses gradle build system.

Add following gradle script in the file.


buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.2.3'
    }
}

apply plugin: 'android-library'

android {
    compileSdkVersion 22
    buildToolsVersion "22.0.1"

    defaultConfig {
        minSdkVersion 8
        targetSdkVersion 22
    }

    sourceSets.main {
        manifest.srcFile 'AndroidManifest.xml'
        java.srcDirs = ['src']
        resources.srcDirs = ['src']
        res.srcDirs = ['res']
        jniLibs.srcDirs = ['libs']
    }
}

Step 5 : 

Add the following line in project.settings file.

include ':tess-two'

Step 6 :

Now we have successfully included the Tess-Two library in our project and we are ready to use it.

First we need to capture the picture itself. You can use something like this code sample taken from Easy OCR Library.


public void takePicture(){
        Intent e = new Intent("android.media.action.IMAGE_CAPTURE");
        this.filePathOriginal = FileUtils.getDirectory(this.directoryPathOriginal) + File.separator + Calendar.getInstance().getTimeInMillis() + ".jpg";
        e.putExtra("output", Uri.fromFile(new File(this.filePathOriginal)));

        startActivity(e);
    }

Or you can find the code here.

We will also downscale the image a little so that the recognition is fast.

You  can use following code sample from again Easy OCR Library


 private Bitmap getBitmapFromPath() {
        BitmapFactory.Options bmOptions = new BitmapFactory.Options();
        bmOptions.inSampleSize = 4;
        Bitmap bitmap = BitmapFactory.decodeFile(this.filePath, bmOptions);
        return bitmap;
    }

Step 7 :

Final step. Recognize the text using the library API.


 private String scanImage(){
        TessBaseAPI baseApi = new TessBaseAPI();
        Log.d(Config.TAG, "Data path : " + FileUtils.getDirectory(this.directoryPath));
        baseApi.init(FileUtils.getDirectory(this.directoryPath) + "/", this.trainedDataCode);
        baseApi.setImage(this.mBitmap);
        String recognizedText = baseApi.getUTF8Text();
        baseApi.end();

        return recognizedText;
    }


Again I would recommend using the Easy OCR Library if you are having facing any problem.

That library has many features :

  1. Very easy setup.
  2. Handles all the image processing part in a background thread.
  3. Provides very interface with relative callbacks for the functions of the library.

 

Android Application for a basic Calculator.

Hi there,

This time would like to share my new project ‘ A basic calculator built for the android platform.’

Creating android apps always seemed cool to me . Able to start  learning  to create one is even cooler.

This project uses simple things like XML layouts, Activities using java, Intents, OnclickListeners and some more basic concepts of java and android.

Below are the screenshots of the app running in both real android device and AVD.

Calculator screenshot
App running on a real android device

 

calculator screnshot
app running on an android emulator.

 

You can download the .apk file of the app from the link below and give it a shot.

https://www.dropbox.com/s/9q7r3jtdg8v6nzx/CalculatorV2.apk

Any comments and suggestions are more then welcome.