First android app developed using Kotlin

I just started learning kotlin since google I/O air in 2017. I brought two books Kotlin in Action by Dmitry Jemerov and Svetlana Isakova and Kotlin for Android Developers by Antonio Leiva.


I developed small application "Tic Tac Toe" both 3x3 and 4x4 , which is published on google play store.


Here is the sample snapshots of Tic Tac Toe from google play store. Please checkout and expecting good suggestion.How do i improved the existing app.

Google Play: Download


#HappyCoding #IloveKotlin

Read More

Override Equal, HashCode and ToString in Kotlin

We all know that override equal(), hashcode() and toString() in java, Here in Kotlin by default implementation, you don't have to need override them. However, if you want to override toString, equals and hashCode, you have to do this.

equals: 

open operator fun equals(other: Any?): Boolean

Indicates whether some other object is "equal to" this one. Implementations must fulfil the following requirements:

• Reflexive: for any non-null reference value x, x.equals(x) should return true.
• Symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
• Transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true
• Consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.

Note that the == operator in Kotlin code is translated into a call to equals when objects on both sides of the operator are not null.

hashCode:

open fun hashCode(): Int

Returns a hash code value for the object. The general contract of hashCode is:

• - Whenever it is invoked on the same object more than once, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified.
• - If two objects are equal according to the equals() method, then calling the hashCode method on each of the two objects must produce the same integer result.

toString:

open fun toString(): String

Returns a string representation of the object.

------------------------------------------------------------

Here is the full implementation kotlin code:

Output looks like

without override equals , hashCode and toString method

false

false

euquals
false

false

toString
co.prandroid.firstkotlin.MainActivity$User@4c83bb6
hashCode
80231350

with override equals , hashCode and toString method

false

true

euquals
false

true

toString
Client(name=john, code=12345)

hashCode
101315726

Reference: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-any/index.html

#HappyCoding #ILoveKotlin

Read More

How to use RecyclerView in Android using Kotlin

Yes, we all love develop mobile application, but some case there is lots boilerplate, null safety problems in java, which is more concise using kotlin.

RecyclerView is a flexible view for providing a limited window into a large data set.It is a modernized version of the ListView and the GridView classes provided by the Android framework. Recycler view addresses several issues that the existing widgets have.

I assume, you have already download latest Android Studio 3.0 preview, If you have not download , please follow the download an install Android Studio 3.0 Preview, which includes Kotlin support out of the box.

RecyclerView allow to use different layout managers for positioning items. Such as LinearLayout, GridLayout and StaggerLayout. I have developing  all there layout and populate data on all the layouts.

Glide used for Image display.

1. First you have to add dependencies on app gradle, following dependencies.

implementation 'com.android.support:recyclerview-v7:25.4.0'
compile 'com.github.bumptech.glide:glide:3.5.2'

2. We must have to make add recyclerview on layout file .


3. Now we have to declear Pojo class in kotlin, which is more easy and simple


4. Create simple data using through object in kotlin.


5. Now, we have make MovieAdapter in Kotlin is simple, which is more complex in java.


6. Declear Recycler view and set layout depend you requirement, like Linear, Grid and Stagger.

7. If you want to make divider in your recycler view , then you using RecyclerView.ItemDecoration.
8. Finally, Application ready to run, and then we have get following snapshots.

To get full source code, please download and fork github repository. Download

#HappyCoding #ILoveKotlin

Read More

Simple use of glide library for display images on android

We know all that memory to store images on mobile is limited, if we have display images using through the bitmap images, it will take lots of memory, which is followed by ultimately memory performance and finally application will be slow.

Yes, we have new image display library call glide. Glide is the perfect and best one to use compared to Picasso and Fresco.

Reasons of using Glide:

1. Recommended by Google and has been used in many Google open source projects.
2. Picasso loads the full-size image (1920x1080 pixels) into the memory and let GPU does the real-time resizing when drawn. While Glide loads the exact ImageView-size (768x432 pixels) into the memory which is a best practice.
3. Glide cache both the full-size image and the resized one. Picasso will cache only single size of image, the full-size one. Glide acts differently, caches separate file for each size of ImageView.
4. GIF (animated image) support.
5. In addition, it also helps preventing an app from popular OutOfMemoryError.

Fresco has huge size of library and cache also. Moreover, app freezes while loading big images from internet into ListView.

While Glide has small size of both library and cache.(Source: Quora)

Here is the pictorial difference between Glide vs Picasso vs Fresco.

Now, How to use Glide to display images on Android, Here is the simple steps,

First you have to introduces dependencies on gradle.

compile 'com.github.bumptech.glide:glide:3.5.2'

and 

On your imageview, please provide this code for display images.

image is image view , depend you requirement, 

In kotlin:

val image = currentView.findViewById(R.id.image) as ImageView

In Java

ImageView image= (ImageView) findViewById(R.id.image)

Now, render the image url on our imageview.

Glide.with(context)

.load(currentVolume.imageUrl)

.into(image)

#HappyCoding #ILoveKotlin

Read More

Hello World and Button Click Event fire in Kotlin (Android) .

We are going to series of kotlin tutorials for android. JetBrains software company introduce new android studio 3.0 in build kotlin plugin, we don't have to add any plugin.
First you have to download Android Studio 3.0 Canary 4 is now available on developer.android.com and learn kotlin from the basic , there is a official documentation of kotlin.
https://kotlinlang.org/.

Let start kotlin

We are going to print simply hello world, then we will moving series of kotlin for android developer.

After finish download android studio, then follow the follow the following steps.


1. Open Android studio 3.0

2. Click File -> New -> New Project.

3. The give the name of Project and you have see by default kotlin plugin checked on android studio.Then click Next.

4. Then choose target Minimum SDK for the application.

5.  Now choose the Activity to mobile, by default there is empty activity, choose this and click next.

6. Finally, when you click finish, then it take few seconds for loading gradles, libraries and other necessary files for mobile application.

Now, your project is created, initially, you can see different then tradition java code because it is kotlin. you simple run the project you have to see, hello world.

I am going to simple change the App, We give the input from EditText and click show Button and display on TextView.

Let start to do this,

Here is the simple layout file:



Here is the simple kotlin code, which is more less and more clear to understand then java code.




Here is the simple output of above program:

I love kotlin and please follow the next tutorials.

Read More

Kotlin For Android Apps

Kotlin is an Android-compatible language that is concise, expressive, and designed to be type- and null-safe. It works with the Java language seamlessly, so it makes it easy for developers who love the Java language to keep using it but also incrementally add Kotlin code and leverage Kotlin libraries. Also, many Android developers have already found that Kotlin makes development faster and more fun, so we want to better support these Kotlin users.

Kotlin is a great fit for developing Android applications, bringing all of the advantages of a modern language to the Android platform without introducing any new restrictions:

• Compatibility: Kotlin is fully compatible with JDK 6, ensuring that Kotlin applications can run on older Android devices with no issues. The Kotlin tooling is fully supported in Android Studio and compatible with the Android build system.
• Performance: A Kotlin application runs as fast as an equivalent Java one, thanks to very similar bytecode structure. With Kotlin's support for inline functions, code using lambdas often runs even faster than the same code written in Java.
• Interoperability: Kotlin is 100% interoperable with Java, allowing to use all existing Android libraries in a Kotlin application. This includes annotation processing, so databinding and Dagger work too.
• Footprint: Kotlin has a very compact runtime library, which can be further reduced through the use of ProGuard. In a real application, the Kotlin runtime adds only a few hundred methods and less than 100K to the size of the .apk file.
• Compilation Time: Kotlin supports efficient incremental compilation, so while there's some additional overhead for clean builds, incremental builds are usually as fast or faster than with Java.
• Learning Curve: For a Java developer, getting started with Kotlin is very easy. The automated Java to Kotlin converter included in the Kotlin plugin helps with the first steps. Kotlin Koans offer a guide through the key features of the language with a series of interactive exercises. 

If want to learn kotlin, today now, please follow the following links

• Download an install Android Studio 3.0 Preview, which includes Kotlin support out of the box.
• Follow the Getting Started with Android and Kotlin tutorial to create your first Kotlin application.
• For a more in-depth introduction, check out the reference documentation on this site and Kotlin Koans.
• Another great resource is Kotlin for Android Developers, a book that guides you step by step through the process of creating a real Android application in Kotlin.
• Check out Google's sample projects written in Kotlin. Source content(KotlinLang)

I am going to write some kotlin tutorials for android and java, based on official website, and other books like kotlin in Action, kotlin for android developer. please follow thing updated my tutorials.

#HaveANiceKotlin #HappyCoding

Read More