Introduction to Factory Pattern on Android

The Factory pattern handles instantiations of objects and abstracts it away from the calling class using a factory method. This is commonly achieved by implementing a specific interface or extending an abstract class in the objects and accessing them through a static method.

How To Set Up A Factory Pattern For Your Project

Create a new project in your Android Studio or whatever IDE you're using. We're going to be building a mini sample app that generates different types of Coffee drinks - who doesn't like coffee!. Let's move on. To keep things simple, I will be focusing on the pattern alone.

The project would return the types of coffee.  Additionally, the sample codes in this tutorial are written in Kotlin, but you can apply the same concepts to Android apps built with Java.

I assumed you've created a new project in your IDE. Now edit the `MainActivity.java` that was generated when you created your project.
Create a new kotlin interface called Coffee.

3. Edit the interface, and create two functions that return string. Name the function `name` and `recipes` respectively.

interface Coffee {
   fun name(): String
   fun recipe(): String
  }

4. Create two classes that implement the Coffee interface.

class CaffeLatte : Coffee {
    override fun name(): String  ="CaffeLatte"
    override fun recipe(): String  ="Expresso"
}

 class Americano : Coffee {
    override fun recipes(): String = "Expresso, Hot water"
    override fun name(): String = "Caffè Americano"
  }

5. Create another kotlin class and call it `CoffeeFactory`. Copy/paste below code snippet into your newly created factory class

object CoffeeFactory {

    enum class Type{
        LATTE, AMERICANO
    }

    fun getCoffee(type: Type): Coffee{
        if (type == CoffeeFactory.Type.LATTE){
            return CafeLatte()
        }else if(type == CoffeeFactory.Type.AMERICANO){
            return Americano()
        }
        throw IllegalArgumentException("Can't handle your command ${type.name}")
    }
}

We're done creating the Factory Pattern, now lets put the pattern into use.

Modify your activity_main.xml layout. Copy/Paste below code in there:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:padding="10dp"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

    <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textStyle="bold"
            android:text="Hello World!"
            android:paddingBottom="5dp"
            android:id="@+id/coffee_name"
            android:textAppearance="?android:textAppearanceMedium"
            app:layout_constraintTop_toTopOf="parent"/>


    <TextView
            android:layout_width="wrap_content"
            android:paddingBottom="10dp"
            android:layout_height="wrap_content"
            android:text="Hello World!"
            android:id="@+id/coffee_recipe"
            android:textAppearance="?android:textAppearanceMedium"
            app:layout_constraintTop_toBottomOf="@id/coffee_name"/>


    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Change Type"
            android:id="@+id/coffee_btn"
            android:textAppearance="?android:textAppearanceMedium"
            app:layout_constraintTop_toBottomOf="@id/coffee_recipe"/>

</android.support.constraint.ConstraintLayout>

Modify the MainActivity.java file. Set up the views properly. The button will be responsible for changing the text when we click it, using the factory method.

class MainActivity : AppCompatActivity() {

    private var isChanged: Boolean =false

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        //Set button click
        coffee_btn.setOnClickListener(this::changeCoffee)

    }

    /**
     * Change coffee recipe and name when button is clicked
     */
    fun changeCoffee(view: View){
        var factory: Coffee
        if (isChanged){
            factory = CoffeeFactory.getCoffee(CoffeeFactory.Type.AMERICANO)
            isChanged = false
        }else{
            factory = CoffeeFactory.getCoffee(CoffeeFactory.Type.LATTE)
            isChanged = true
        }

        changeCoffeeType(factory.recipes(), factory.name())
    }

    /**
     * Method that changes the coffee type
     */
    private fun changeCoffeeType(recipe: String, name: String){

        coffee_recipe.text = recipe

        coffee_name.text =name
    }
}

Yay! we're done. Now you can run your app on real device or emulator. If you have any questions regarding this tutorial, please let me know through the comment section.

Makemecode

Introduction to Factory Pattern on Android

How To Set Up A Factory Pattern For Your Project