Develop Reference

How to add a gesture detector to a view in Android

I was struggling with adding a gesture detector to a subview in my project. Do I override the parent's onTouchEvent or the child's onTouchEvent? Do I make an OnTouchListener and add the gesture detector there? The documentation shows an example for how to add a gesture detector to the activity itself but it is not clear how to add it to a view. The same process could be used if subclassing a view (example here), but I want to add the gesture without subclassing anything.
This is the closest other question I could find but it is specific to a fling gesture on an ImageView, not to the general case of any View. Also there is some disagreement in those answers about when to return true or false.
To help myself understand how it works, I made a stand alone project. My answer is below.

This example shows how to add a gesture detector to a view. The layout is just a single View inside of an Activity. You can use the same method to add a gesture detector to any type of view.
We will add the gesture detector to the green View.
MainActivity.java
The basic idea is to add an OnTouchListener to the view. Normally we would get all the raw touch data here (like ACTION_DOWN, ACTION_MOVE, ACTION_UP, etc.), but instead of handling it ourselves, we will forward it on to a gesture detector to do the interpretation of the touch data.
We are using a SimpleOnGestureListener. The nice thing about this gesture detector is that we only need to override the gestures that we need. In the example here I included a lot of them. You can remove the ones you don't need. (You should always return true in onDown(), though. Returning true means that we are handling the event. Returning false will make the system stop giving us any more touch events.)
public class MainActivity extends AppCompatActivity {
private GestureDetector mDetector;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// this is the view we will add the gesture detector to
View myView = findViewById(R.id.my_view);
// get the gesture detector
mDetector = new GestureDetector(this, new MyGestureListener());
// Add a touch listener to the view
// The touch listener passes all its events on to the gesture detector
myView.setOnTouchListener(touchListener);
}
// This touch listener passes everything on to the gesture detector.
// That saves us the trouble of interpreting the raw touch events
// ourselves.
View.OnTouchListener touchListener = new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
// pass the events to the gesture detector
// a return value of true means the detector is handling it
// a return value of false means the detector didn't
// recognize the event
return mDetector.onTouchEvent(event);
}
};
// In the SimpleOnGestureListener subclass you should override
// onDown and any other gesture that you want to detect.
class MyGestureListener extends GestureDetector.SimpleOnGestureListener {
#Override
public boolean onDown(MotionEvent event) {
Log.d("TAG","onDown: ");
// don't return false here or else none of the other
// gestures will work
return true;
}
#Override
public boolean onSingleTapConfirmed(MotionEvent e) {
Log.i("TAG", "onSingleTapConfirmed: ");
return true;
}
#Override
public void onLongPress(MotionEvent e) {
Log.i("TAG", "onLongPress: ");
}
#Override
public boolean onDoubleTap(MotionEvent e) {
Log.i("TAG", "onDoubleTap: ");
return true;
}
#Override
public boolean onScroll(MotionEvent e1, MotionEvent e2,
float distanceX, float distanceY) {
Log.i("TAG", "onScroll: ");
return true;
}
#Override
public boolean onFling(MotionEvent event1, MotionEvent event2,
float velocityX, float velocityY) {
Log.d("TAG", "onFling: ");
return true;
}
}
}
It is a quick setup to run this project, so I recommend you try it out. Notice how and when the log events occur.

short version in kotlin to detect double tap only for a view:
val gestureDetector = GestureDetector(activity, object : GestureDetector.SimpleOnGestureListener() {
override fun onDoubleTap(e: MotionEvent?): Boolean {
Log.d("myApp", "double tap")
return true
}
})
myView.setOnTouchListener { _, event -> gestureDetector.onTouchEvent(event) }
and don't forget to make myView clickable

OnTouchListener on entire Activity

I'm trying to detect a onFling event on the entire area of my activity. To do this I:
1) set the GestureDetectorCompat:
private GestureDetectorCompat gDetect;
2) in OnCreate initialize the detector:
gDetect = new GestureDetectorCompat(this, new GestureListener());
3) override the onTouchEvent:
#Override
public boolean onTouchEvent(MotionEvent event) {
gDetect.onTouchEvent(event);
return super.onTouchEvent(event);
}
4) create the GestureListener class:
class GestureListener extends GestureDetector.SimpleOnGestureListener {
#Override
public boolean onDown(MotionEvent event) {
return true;
}
#Override
public boolean onFling(MotionEvent event1, MotionEvent event2,
float velocityX, float velocityY) {
Log.e(null, "onFling: " + event1.toString() + event2.toString());
return super.onFling(event1, event2, velocityX, velocityY);
}
}
It works, but it detects onFling gesture ONLY in the part of my UI where there is not any other view. So, if I swipe in a blank area it works, if I swipe in a part of the activity where is another view (for example a ScrollView or a LinearLayout) the detection isn't triggered.
I hope I've explained my problem: how I can detect gesture on the entire surface of the Activity, to accomplish a simple swipe gesture?
Many tanks.

You can use GestureOverlayView. Here is a great starter resource for GestureOverlayView . Also you can have a look at this SO question.
Basically to use this your application must use the view "GestureOverlayView" and you place your other views in this view. Your activity must implement the interface "OnGesturePerformedListener" and if a gesture is detected then "onGesturePerformedListener" method is called.
Hope this helps. Goodluck!

Implementing onTouchListener and onGestureLitener simultaneously

I am facing a situation.
I have written a class implementing onTouchListener which I have registered with view(GLSurfaceView, to be precise) and I used it to extract all
information about touch events. And it serves me very well. And implementing onTouch
method means that event is handled then and there and its not propagated down.
But of late I need to implement swipe functionality for my game. And it needs that I implement
onTouchEvent for my view. But as my onTouchListener implementation class is already implementing onTouch method, so onTouchEvent won't be called. And I want to keep my onTouchListener implementation.
Please tell me how to solve this issue.
Manish

In your class put the following:
//not necessarily OnCreate but put it in whatever constructor your class uses
OnCreate(Context context){
mGestureDetector = new GestureDetector(context, new CustomGestureListener());
}
#Override
public boolean onTouchEvent(MotionEvent event) {
mGestureDetector.onTouchEvent(event);
return super.onTouchEvent(event);
}
private final GestureDetector mGestureDetector;
private class CustomGestureListener extends SimpleOnGestureListener {
#Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
//get the fling
}
}
This allows the onTouchEvent to execute, but it also checks for a gesture event as well by calling the gesture detector within the onTouchEvent.
See also this answer: How to set OnTouchListener for the entire screen?

Android ListView tolerance

I have list items that have a HorizontalScrollView in each of them. Hence, I should be able to swipe up and down the list and also swipe through the list item horizontally. (e.g. Pulse News App).
What I'm encountering is that, whenever I scroll the HorizontalScrollView, the ListView also gets scrolled by tiny bit but giving out annoying disturbances in terms of User Experience.
So, I was actually thinking to subclass ListView and implement my own ListView widget. However, I don't know which method to override so that I could increase X tolerance and stop the listview from giving these unwanted flickering.

gestureDetector = new GestureDetector(new YScrollDetector());
public boolean onInterceptTouchEvent(MotionEvent ev) {
//Call super first because it does some hidden motion event handling
boolean result = super.onInterceptTouchEvent(ev);
//Now see if we are scrolling vertically with the custom gesture detector
if (gestureDetector.onTouchEvent(ev)) {
return result;
}
//If not scrolling vertically (more y than x), don't hijack the event.
else {
return false;
}
}
// Return false if we're scrolling in the x direction
class YScrollDetector extends SimpleOnGestureListener {
#Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
try {
if (Math.abs(distanceY) > Math.abs(distanceX)) {
return true;
} else {
return false;
}
} catch (Exception e) {
// nothing
}
return false;
}
}
This is will help you, you have to override these in the custom list view you create,i used this to eliminate the problem in my application. Hope this helps.

Handling UI Events in Android

I'm trying to modify some code I found online to my needs. It is supposed to catch a MotionEvent (a fling in particular) and launch a separate activity. I am new to java, so I'm having some trouble understanding the code. Here's what I have so far:
public class Hypertension extends Activity {
private GestureDetector flingDetector;
View.OnTouchListener gestureListener;
private TextView redView;
private TextView greenView;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
redView = (TextView)findViewById(R.id.buttonRed);
greenView = (TextView)findViewById(R.id.buttonGreen);
redView.setOnTouchListener(gestureListener);
greenView.setOnTouchListener(gestureListener);
flingDetector = new GestureDetector(new MyFlingListener());
gestureListener = new View.OnTouchListener() {
public boolean onTouch(View v, MotionEvent event) {
if (flingDetector.onTouchEvent(event)) {
//startActivity(new Intent(Hypertension.this, Green.class));
return true;
}
return false;
}
};
}
class MyFlingListener extends SimpleOnGestureListener {
#Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
float velocityY) {
// TODO Auto-generated method stub
startActivity(new Intent(Hypertension.this, Green.class));
return false;
}
}
#Override
public boolean onTouchEvent(MotionEvent event) {
if (flingDetector.onTouchEvent(event))
return true;
else
return false;
}
}
My understanding is that when the screen is touched, onTouchEvent is called. In the above code, this method is overridden to call flingDetector, which listens for a fling. If one is heard, it launches the activity.
As of now, however, nothing happens when I perform a fling in the emulator. Also, I am fairly confused as to what the return values of the various boolean methods actually represent.

You have two onTouchEvent methods in your code. One is in the GestureDetector class (not overridden), and the other is in your Hypertension activity class (which you have overridden at the bottom).
When someone triggers the TouchEvent in the main activity you explicitly calling the GestureDetector one (passing down the event) here:
if (flingDetector.onTouchEvent(event)) return true;
But if you haven't overridden the onTouchEvent method of that class then nothing is going to happen!
The purpose of overriding these "onSomething()" methods is so that they will get called automatically when an event triggers. In general the way to work with listeners is as follows:
Create a subclass of the Listener class for the event and override its "onEvent()" method to do something when the event is triggered
Call the "setListener( Listener)" method of the object you want to trigger said events after it has been initialized--passing in your previously created Listener
Sit back and watch :)

For all event listeners that return a boolean it should return true when it handles the event, so in your example if the flingDetector handles the onTouchEvent it returns true.
This question has been posed before and there are some great answers there.