How to draw a smooth line following my finger using Kotlin?

This example demonstrates how to draw a smooth line following my finger using Android Kotlin.

Step 1 − Create a new project in Android Studio, go to File ? New Project and fill all required details to create a new project.

Step 2 − Add the following code to res/layout/activity_main.xml.

<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context=".MainActivity">    <TextView       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:layout_centerInParent="true"       android:text="Draw lines on the Activity"       android:textAlignment="center"       android:textColor="@android:color/background_dark"       android:textSize="32sp"       android:textStyle="bold" />    <ImageView       android:id="@+id/imageView"       android:layout_width="wrap_content"       android:layout_height="match_parent"       android:layout_alignParentStart="true"       android:layout_alignParentTop="true"       android:layout_alignParentEnd="true"       android:contentDescription="TODO" /> </RelativeLayout>

Step 3 − Add the following code to src/MainActivity.kt

import android.graphics.Bitmap import android.graphics.Canvas import android.graphics.Color import android.graphics.Paint import android.os.Bundle import android.view.MotionEvent import android.view.View import android.widget.ImageView import androidx.appcompat.app.AppCompatActivity class MainActivity : AppCompatActivity(), View.OnTouchListener {    private lateinit var imageView: ImageView    private var bitmap: Bitmap? = null    var canvas: Canvas? = null    var paint: Paint? = null    var downX = 0f    var downY: kotlin.Float = 0f    var upX: kotlin.Float = 0f    var upY: kotlin.Float = 0f    override fun onCreate(savedInstanceState: Bundle?) {       super.onCreate(savedInstanceState)       setContentView(R.layout.activity_main)       title = "KotlinApp"       imageView = findViewById(R.id.imageView)       val currentDisplay = windowManager.defaultDisplay       val dw = currentDisplay.width.toFloat()       val dh = currentDisplay.height.toFloat()       bitmap = Bitmap.createBitmap(dw.toInt(), dh.toInt(), Bitmap.Config.ARGB_8888)       canvas = Canvas(bitmap)       paint = Paint()       paint!!.color = Color.RED       paint!!.strokeWidth = 10F       imageView.setImageBitmap(bitmap)       imageView.setOnTouchListener(this)    }    override fun onTouch(v: View?, event: MotionEvent?): Boolean {       when (event!!.action) {          MotionEvent.ACTION_DOWN -> {             downX = event.x             downY = event.y          }          MotionEvent.ACTION_MOVE -> {       }       MotionEvent.ACTION_UP -> {           upX = event.x           upY = event.y           canvas!!.drawLine(downX, downY, upX, upY, paint)           imageView.invalidate()       }       MotionEvent.ACTION_CANCEL -> {       }       else -> {       }     }     return true    } }

Step 4 − Add the following code to androidManifest.xml

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="app.com.kotlipapp">    <application       android:allowBackup="true"       android:icon="@mipmap/ic_launcher"       android:label="@string/app_name"       android:roundIcon="@mipmap/ic_launcher_round"       android:supportsRtl="true"       android:theme="@style/AppTheme">       <activity android:name=".MainActivity">          <intent-filter>             <action android:name="android.intent.action.MAIN" />             <category android:name="android.intent.category.LAUNCHER" />          </intent-filter>       </activity>    </application> </manifest>

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click the Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen −

Click here to download the project code.