Introduction

The gesture means finger movement in the touchscreen interface. The different types of gestures are Tab, drag, Flick, Swipe, double tab, pinch, Three-finger pinch, three-finger swipe, touch and hold, rotate, shake. In this article, we are going to learn how to implement gestures in our application.
Xamarin.Android - Gesture Detector
Let's begin.
Create a Xamarin android project in Visual Studio 2019. Go to Visual Studio >> Create New Project >> select Android App (Xamarin) and click Next. In the next dialog box, give Project Name, Location Name, Location and click the Create button.
Xamarin.Android - Gesture Detector
After the project creation, open content_main.xml file and add TextView widget in the screen and set width and height as match_parent. The code is given below:
  1. <?xml version="1.0" encoding="utf-8"?>
  2. <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  3. xmlns:app="http://schemas.android.com/apk/res-auto"
  4. xmlns:tools="http://schemas.android.com/tools"
  5. android:layout_width="match_parent"
  6. android:layout_height="match_parent"
  7. tools:showIn="@layout/activity_main">
  9. <TextView
  10. android:id="@+id/imageView"
  11. android:layout_width="match_parent"
  12. android:text="Gesture"
  13. android:textSize="35dp"
  14. android:gravity="center"
  15. android:layout_centerInParent="true"
  16. android:textColor="@android:color/black"
  17. android:layout_height="match_parent"/>
  19. </RelativeLayout>
Next, open the MainActivity.cs class by double-clicking it. The gesture interfaces are going to implement in this MainActivity. This Interfaces will create the following gesture methods:
  • OnDown
  • OnScroll
  • OnSingleTabUp
  • OnLongPress
  • OnFling
  • OnShowPress
The Method definitions are here:
  • OnDown(MotionEvent e) – Down MotionEvent will get triggers. One Touch or tab the UI
  • OnFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) - Notifies of swipe occurs in the start and end of MotionEvent or threshold of swipe.
  • OnLongPress(MotionEvent e) - This event will get trigger. Once long touch or tab the UI
  • OnScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) - While scrolling this event will be triggered.
  • OnShowPress(MotionEvent e) - performed a done MotionEvent and not above performed a moment.
  • OnSingleTapUp(MotionEvent e) - On single tab, the widget or layout this event will be triggered.
Based on the Fling start and end velocity, we can set the swipe directions:
  1. Top to Bottom
  2. Bottom to Top
  3. Right to Left
  4. Left to Right.
Velocity has two types:
  1. Swipe Threshold - The difference between the initial and final position of touch in any four directions that we already have seen.
  2. Velocity Threshold - How quickly the gesture is swiped.
Finally, set this interface to the TextView we already designed in content_main.xml. The page code is given below
  1. using System;
  2. using Android.App;
  3. using Android.OS;
  4. using Android.Runtime;
  5. using Android.Support.Design.Widget;
  6. using Android.Support.V7.App;
  7. using Android.Views;
  8. using Android.Widget;
  9. using static Android.Views.GestureDetector;
  10. using static Android.Views.View;
  11. namespace TVS_Demo {
  12. [Activity(Theme = "@style/AppTheme.NoActionBar", MainLauncher = true, ScreenOrientation = Android.Content.PM.ScreenOrientation.Portrait)]
  13. public class MainActivity: AppCompatActivity, IOnTouchListener, IOnGestureListener {
  14. private TextView txtGestureView;
  15. private readonly int SWIPE_MIN_DISTANCE = 120;
  16. private static int SWIPE_MAX_OFF_PATH = 250;
  17. private static int SWIPE_THRESHOLD_VELOCITY = 200;
  18. private int imageIndex = 0;
  19. private GestureDetector gestureDetector;
  20. protected override void OnCreate(Bundle savedInstanceState) {
  21. base.OnCreate(savedInstanceState);
  22. Xamarin.Essentials.Platform.Init(this, savedInstanceState);
  23. SetContentView(Resource.Layout.activity_main);
  24. txtGestureView = FindViewById < TextView > (Resource.Id.imageView);
  25. gestureDetector = new GestureDetector(this);
  26. txtGestureView.SetOnTouchListener(this);
  27. }
  28. public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults) {
  29. Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);
  30. base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
  31. }
  32. public bool OnTouch(View v, MotionEvent e) {
  33. Toast.MakeText(this, "On Touch", ToastLength.Short).Show();
  34. return gestureDetector.OnTouchEvent(e);
  35. }
  36. public bool OnDown(MotionEvent e) {
  37. Toast.MakeText(this, "On Down", ToastLength.Short).Show();
  38. return true;
  39. }
  40. public bool OnFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
  41. bool result = false;
  42. try {
  43. float diffY = e2.GetY() - e1.GetY();
  44. float diffX = e2.GetX() - e1.GetX();
  45. if (Math.Abs(diffX) > Math.Abs(diffY)) {
  46. if (Math.Abs(diffX) > SWIPE_THRESHOLD_VELOCITY && Math.Abs(velocityX) > SWIPE_THRESHOLD_VELOCITY) {
  47. if (diffX > 0) {
  48. //onSwipeRight();
  49. if (imageIndex > 0) {
  50. imageIndex--;
  51. }
  52. txtGestureView.Text = "Swiped Right";
  53. } else {
  54. if (imageIndex < 28) {
  55. imageIndex++;
  56. }
  57. //onSwipeLeft();
  58. txtGestureView.Text = "Swiped Left";
  59. }
  60. result = true;
  61. }
  62. } else
  63. if (Math.Abs(diffY) > SWIPE_THRESHOLD_VELOCITY && Math.Abs(velocityY) > SWIPE_THRESHOLD_VELOCITY) {
  64. if (diffY > 0) {
  65. //onSwipeBottom();
  66. txtGestureView.Text = "Swiped Bottom";
  67. } else {
  68. //onSwipeTop();
  69. txtGestureView.Text = "Swiped Top";
  70. }
  71. result = true;
  72. }
  73. } catch (Exception exception) {
  74. Console.WriteLine(exception.Message);
  75. }
  76. return result;
  77. }
  78. public void OnLongPress(MotionEvent e) {
  79. Toast.MakeText(this, "On Long Press", ToastLength.Short).Show();
  80. }
  81. public bool OnScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
  82. Toast.MakeText(this, "On Scroll", ToastLength.Short).Show();
  83. return true;
  84. }
  85. public void OnShowPress(MotionEvent e) {
  86. Toast.MakeText(this, "On Show Press", ToastLength.Short).Show();
  87. }
  88. public bool OnSingleTapUp(MotionEvent e) {
  89. Toast.MakeText(this, "On Single Tab Up", ToastLength.Short).Show();
  90. return true;
  91. }
  92. }
  93. }
Run your application and get output, as shown in the below gif.
Xamarin.Android - Gesture Detector
The full source code is here - GitHub

Conclusion

I hope you all understood the gestures and how to implement them in our applications. Thanks for reading!