MVP in Android

Overview

MVP stands for Model-View-Presenter. MVP overcomes the challenges of MVC. It provides modularity, testability and a more clean codebase. 

Key points of MVP architecture

1. Communication between View-Presenter and Model-Presenter happens with the help of an interface.
2. One Presenter manages one View at a time.
3. Model and View doesn't have knowledge about each other. 

Steps to follow

• Create an interface to communicate between View-Presenter and Model-Presenter

 interface Contract
 {
    /* This interface is used for view */
    interface View
    {
        /* Shows the progress bar */
        fun showProgressBar()

        /* Hides the progress bar */
        fun hideProgressBar()

        /* Sets the text of the view with the String */
        fun setString(string : String?)
    }

    interface Model
    {
        interface OnFinished
        {
            fun finish(string : String?)
        }

        // This function is used to check if the String is set
        fun goNext(onFinished : OnFinished)
    }

    interface Presenter
    {
        /* This function is used for the button of view */
        fun onNextClick()

        /* This function is used to destroy the view */
        fun onDestroy()
    }
 }

• Create a Model class and implement the interface that you created for Model-Presenter

 class Model : Contract.Model
 {
    private val arrayList = listOf(
        "DSA Self Paced: Master the basics of Data Structures and Algorithms to solve complex problems efficiently. " ,
        "Placement 100: This course will guide you for placement with theory, lecture videos, weekly assignments contests and doubt assistance." ,
        "Amazon SDE Test Series: Test your skill & give the final touch to your preparation before applying for product based against like Amazon, Microsoft, etc." ,
        "Complete Interview Preparation: Cover all the important concepts and topics required for the interviews. Get placement ready before the interviews begin" ,
        "Low Level Design for SDE 1 Interview: Learn Object-oriented Analysis and Design to prepare for SDE 1 Interviews in top companies"
    )

    override fun goNext(onFinished : Contract.Model.OnFinished)
    {
        Handler(Looper.getMainLooper()).postDelayed({
            onFinished.finish(getRandomString)
        } , 1200)
    }

    private val getRandomString : String
        private get()
        {
            val random = Random()
            val index = random.nextInt(arrayList.size)
            return arrayList[index]
        }

 }

• Create a Presenter class and implement the interface of Presenter and an interface of Model

 class Presenter(private var mainView : Contract.View? , private val model : Contract.Model) :
    Contract.Presenter , Contract.Model.OnFinished
 {
    override fun onNextClick()
    {
        if (mainView != null)
        {
            mainView !!.showProgressBar()
        }
        model.goNext(this)
    }

    override fun onDestroy()
    {
        mainView = null
    }

    override fun finish(string : String?)
    {
        if (mainView != null)
        {
            mainView?.setString(string)
            mainView?.hideProgressBar()
        }
    }
 }

• Create a View class and implement the interface that you created for View-Presenter

 class MainActivity : AppCompatActivity() , Contract.View
 {
    private var presenter : Presenter? = null
    override fun onCreate(savedInstanceState : Bundle?)
    {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        presenter = Presenter(this , Model())
        btnNext.setOnClickListener {
            presenter !!.onNextClick()
        }
    }

    override fun showProgressBar()
    {
        progressBar !!.visibility = View.VISIBLE
        textView !!.visibility = View.VISIBLE
    }

    override fun hideProgressBar()
    {
        progressBar !!.visibility = View.GONE
        textView !!.visibility = View.VISIBLE
    }

    override fun setString(string : String?)
    {
        textView !!.text = string
    }

    override fun onDestroy()
    {
        super.onDestroy()
        presenter !!.onDestroy()
    }
 }

Reference

1. https://www.geeksforgeeks.org/mvp-model-view-presenter-architecture-pattern-in-android-with-example/
   
2. https://github.com/iamraajkanchan/MVP_Android