How to handle swipe gestures in Kotlin?

Kotlin Apps/ApplicationsMobile Development

This example demonstrates how to handle swipe gestures in an android device using 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:id="@+id/relativeLayout"
   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="Swipe Left, right, up and down to detect Swipe Gesture"
      android:textAlignment="center"
      android:textSize="16sp"
      android:textStyle="bold" />
</RelativeLayout>

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

package app.com.kotlinapp
import android.os.Bundle
import android.widget.RelativeLayout
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
   private lateinit var layout: RelativeLayout
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      layout = findViewById(R.id.relativeLayout)
      layout.setOnTouchListener(object : OnSwipeTouchListener(this@MainActivity) {
         override fun onSwipeLeft() {
            super.onSwipeLeft()
            Toast.makeText(this@MainActivity, "Swipe Left gesture detected",
            Toast.LENGTH_SHORT)
            .show()
         }
         override fun onSwipeRight() {
            super.onSwipeRight()
            Toast.makeText(
               this@MainActivity,
               "Swipe Right gesture detected",
               Toast.LENGTH_SHORT
            ).show()
         }
         override fun onSwipeUp() {
            super.onSwipeUp()
            Toast.makeText(this@MainActivity, "Swipe up gesture detected", Toast.LENGTH_SHORT)
            .show()
         }
         override fun onSwipeDown() {
            super.onSwipeDown()
            Toast.makeText(this@MainActivity, "Swipe down gesture detected", Toast.LENGTH_SHORT)
            .show()
         }
      })
   }
}

Step 4 − Add the following code to src/OnSwipeTouchListener.kt

package app.com.kotlinapp
import android.content.Context
import android.view.GestureDetector
import android.view.GestureDetector.SimpleOnGestureListener
import android.view.MotionEvent
import android.view.View
import android.view.View.OnTouchListener
import kotlin.math.abs
internal open class OnSwipeTouchListener(c: Context?) :
OnTouchListener {
   private val gestureDetector: GestureDetector
   override fun onTouch(view: View, motionEvent: MotionEvent): Boolean {
      return gestureDetector.onTouchEvent(motionEvent)
   }
   private inner class GestureListener : SimpleOnGestureListener() {
      private val SWIPE_THRESHOLD: Int = 100
      private val SWIPE_VELOCITY_THRESHOLD: Int = 100
      override fun onDown(e: MotionEvent): Boolean {
         return true
      }
      override fun onSingleTapUp(e: MotionEvent): Boolean {
         onClick()
         return super.onSingleTapUp(e)
      }
      override fun onDoubleTap(e: MotionEvent): Boolean {
         onDoubleClick()
         return super.onDoubleTap(e)
      }
      override fun onLongPress(e: MotionEvent) {
         onLongClick()
         super.onLongPress(e)
      }
      override fun onFling(
         e1: MotionEvent,
         e2: MotionEvent,
         velocityX: Float,
         velocityY: Float
      ): Boolean {
         try {
            val diffY = e2.y - e1.y
            val diffX = e2.x - e1.x
            if (abs(diffX) > abs(diffY)) {
               if (abs(diffX) > SWIPE_THRESHOLD && abs(
                  velocityX
               ) > SWIPE_VELOCITY_THRESHOLD
            ) {
               if (diffX > 0) {
                  onSwipeRight()
               }
               else {
                  onSwipeLeft()
               }
            }
         }
          else {
            if (abs(diffY) > SWIPE_THRESHOLD && abs(
               velocityY
            ) > SWIPE_VELOCITY_THRESHOLD
         ) {
            if (diffY < 0) {
               onSwipeUp()
            }
            else {
                  onSwipeDown()
                  }
               }
               }
         } catch (exception: Exception) {
         exception.printStackTrace()
      }
      return false
      }
   }
   open fun onSwipeRight() {}
   open fun onSwipeLeft() {}
   open fun onSwipeUp() {}
   open fun onSwipeDown() {}
   private fun onClick() {}
   private fun onDoubleClick() {}
   private fun onLongClick() {}
   init {
      gestureDetector = GestureDetector(c, GestureListener())
   }
}

Step 5 − 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.

raja
Published on 20-Apr-2020 13:10:58
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