Fling gesture detection on grid layout

Question

I want to get fling gesture detection working in my Android application.

What I have is a GridLayout that contains 9 ImageViews. The source can be found here: Romain Guys's Grid Layout.

That file I take is from Romain Guy's Photostream application and has only been slightly adapted.

For the simple click situation I need only set the onClickListener for each ImageView I add to be the main activity which implements View.OnClickListener. It seems infinitely more complicated to implement something that recognizes a fling. I presume this is because it may span views?

• If my activity implements OnGestureListener I don't know how to set that as the gesture listener for the Grid or the Image views that I add.

  public class SelectFilterActivity extends Activity implements
     View.OnClickListener, OnGestureListener { ...
  

• If my activity implements OnTouchListener then I have no onFling method to override (it has two events as parameters allowing me to determine if the fling was noteworthy).

  public class SelectFilterActivity extends Activity implements
      View.OnClickListener, OnTouchListener { ...
  

• If I make a custom View, like GestureImageView that extends ImageView I don't know how to tell the activity that a fling has occurred from the view. In any case, I tried this and the methods weren't called when I touched the screen.

I really just need a concrete example of this working across views. What, when and how should I attach this listener? I need to be able to detect single clicks also.

// Gesture detection
mGestureDetector = new GestureDetector(this, new GestureDetector.SimpleOnGestureListener() {

    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
        int dx = (int) (e2.getX() - e1.getX());
        // don't accept the fling if it's too short
        // as it may conflict with a button push
        if (Math.abs(dx) > MAJOR_MOVE && Math.abs(velocityX) > Math.absvelocityY)) {
            if (velocityX > 0) {
                moveRight();
            } else {
                moveLeft();
            }
            return true;
        } else {
            return false;
        }
    }
});

Is it possible to lay a transparent view over the top of my screen to capture flings?

If I choose not to inflate my child image views from XML can I pass the GestureDetector as a constructor parameter to a new subclass of ImageView that I create?

This is the very simple activity that I'm trying to get the fling detection to work for: SelectFilterActivity (Adapted from photostream).

I've been looking at these sources:

• Detect Gestures - Tutorial

• SDK docs

• Calculator Code

Nothing has worked for me so far and I was hoping for some pointers.

Answer 1

There's some proposition over the web (and this page) to use ViewConfiguration.getScaledTouchSlop() to have a device-scaled value for SWIPE_MIN_DISTANCE.

getScaledTouchSlop() is intended for the "scrolling threshold" distance, not swipe. The scrolling threshold distance has to be smaller than a "swing between page" threshold distance. For example, this function returns 12 pixels on my Samsung GS2, and the examples quoted in this page are around 100 pixels.

With API Level 8 (Android 2.2, Froyo), you've got getScaledPagingTouchSlop(), intended for page swipe. On my device, it returns 24 (pixels). So if you're on API Level < 8, I think "2 * getScaledTouchSlop()" should be the "standard" swipe threshold. But users of my application with small screens told me that it was too few... As on my application, you can scroll vertically, and change page horizontally. With the proposed value, they sometimes change page instead of scrolling.

Answer 2

You can use the droidQuery library to handle flings, clicks, long clicks, and custom events. The implementation is built on my previous answer below, but droidQuery provides a slick, simple syntax:

//global variables    private boolean isSwiping = false;
private SwipeDetector.Direction swipeDirection = null;
private View v;//must be instantiated before next call.

//swipe-handling code
$.with(v).swipe(new Function() {
    @Override
    public void invoke($ droidQuery, Object... params) {
        if (params[0] == SwipeDetector.Direction.START)
            isSwiping = true;
        else if (params[0] == SwipeDetector.Direction.STOP) {
            if (isSwiping) {                    isSwiping = false;
                if (swipeDirection != null) {
                    switch(swipeDirection) {
                        case DOWN :                                //TODO: Down swipe complete, so do something
                            break;
                        case UP :
                            //TODO: Up swipe complete, so do something
                            break;
                        case LEFT :
                            //TODO: Left swipe complete, so do something
                            break;
                        case RIGHT :
                            //TODO: Right swipe complete, so do something
                            break;
                        default :                                break;
                    }
                }                }
        }
        else {
            swipeDirection = (SwipeDetector.Direction) params[0];
        }
    }
});

Original Answer

This answer uses a combination of components from the other answers here. It consists of the SwipeDetector class, which has an inner interface for listening for events. I also provide a RelativeLayout to show how to override a View's onTouch method to allow both swipe events and other detected events (such as clicks or long clicks).

SwipeDetector

package self.philbrown;

import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;

/**
 * Detect Swipes on a per-view basis. Based on original code by Thomas Fankhauser on StackOverflow.com,
 * with adaptations by other authors (see link).
 * @author Phil Brown
 * @see <a href="http://stackoverflow.com/questions/937313/android-basic-gesture-detection">android-basic-gesture-detection</a>
 */
public class SwipeDetector implements View.OnTouchListener
{
    /**
     * The minimum distance a finger must travel in order to register a swipe event.
     */
    private int minSwipeDistance;

    /** Maintains a reference to the first detected down touch event. */
    private float downX, downY;

    /** Maintains a reference to the first detected up touch event. */
    private float upX, upY;

    /** provides access to size and dimension contants */
    private ViewConfiguration config;

    /**
     * provides callbacks to a listener class for various swipe gestures.
     */
    private SwipeListener listener;

    public SwipeDetector(SwipeListener listener)
    {
        this.listener = listener;
    }


    /**
     * {@inheritDoc}
     */
    public boolean onTouch(View v, MotionEvent event)
    {
        if (config == null)
        {
                config = ViewConfiguration.get(v.getContext());
                minSwipeDistance = config.getScaledTouchSlop();
        }

        switch(event.getAction())
        {
        case MotionEvent.ACTION_DOWN:
            downX = event.getX();
            downY = event.getY();
            return true;
        case MotionEvent.ACTION_UP:
            upX = event.getX();
            upY = event.getY();

            float deltaX = downX - upX;
            float deltaY = downY - upY;

            // swipe horizontal?
            if(Math.abs(deltaX) > minSwipeDistance)
            {
                // left or right
                if (deltaX < 0)
                {
                        if (listener != null)
                        {
                                listener.onRightSwipe(v);
                                return true;
                        }
                }
                if (deltaX > 0)
                {
                        if (listener != null)
                        {
                                listener.onLeftSwipe(v);
                                return true;
                        }
                }
            }

            // swipe vertical?
            if(Math.abs(deltaY) > minSwipeDistance)
            {
                // top or down
                if (deltaY < 0)
                {
                        if (listener != null)
                        {
                                listener.onDownSwipe(v);
                                return true;
                        }
                }
                if (deltaY > 0)
                {
                        if (listener != null)
                        {
                                listener.onUpSwipe(v);
                                return true;
                        }
                }
            }
        }
        return false;
    }

    /**
     * Provides callbacks to a registered listener for swipe events in {@link SwipeDetector}
     * @author Phil Brown
     */
    public interface SwipeListener
    {
        /** Callback for registering a new swipe motion from the bottom of the view toward its top. */
        public void onUpSwipe(View v);
        /** Callback for registering a new swipe motion from the left of the view toward its right. */
        public void onRightSwipe(View v);
        /** Callback for registering a new swipe motion from the right of the view toward its left. */
        public void onLeftSwipe(View v);
        /** Callback for registering a new swipe motion from the top of the view toward its bottom. */
        public void onDownSwipe(View v);
    }
}

Swipe Interceptor View

package self.philbrown;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.RelativeLayout;

import com.npeinc.module_NPECore.model.SwipeDetector;
import com.npeinc.module_NPECore.model.SwipeDetector.SwipeListener;

/**
 * View subclass used for handling all touches (swipes and others)
 * @author Phil Brown
 */
public class SwipeInterceptorView extends RelativeLayout
{
    private SwipeDetector swiper = null;

    public void setSwipeListener(SwipeListener listener)
    {
        if (swiper == null)
            swiper = new SwipeDetector(listener);
    }

    public SwipeInterceptorView(Context context) {
        super(context);
    }

    public SwipeInterceptorView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public SwipeInterceptorView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public boolean onTouchEvent(MotionEvent e)
    {
        boolean swipe = false, touch = false;
        if (swiper != null)
            swipe = swiper.onTouch(this, e);
        touch = super.onTouchEvent(e);
        return swipe || touch;
    }
}

Answer 3

One of the answers above mentions handling different pixel density but suggests computing the swipe parameters by hand. It is worth noting that you can actually obtain scaled, reasonable values from the system using ViewConfiguration class:

final ViewConfiguration vc = ViewConfiguration.get(getContext());
final int swipeMinDistance = vc.getScaledPagingTouchSlop();
final int swipeThresholdVelocity = vc.getScaledMinimumFlingVelocity();
final int swipeMaxOffPath = vc.getScaledTouchSlop();
// (there is also vc.getScaledMaximumFlingVelocity() one could check against)

I noticed that using these values causes the "feel" of fling to be more consistent between the application and rest of system.

Answer 4

I nedded a more generic Class , I took Tomas's class and added an Interface that send events to your Activity or Fragment. it will register the listener on the constructor so be sure you implement the interface or an ClassCastException will be thorwn. the interface returns one of the four final int defined in the class and will return the view on which it was activated upon.

import android.app.Activity;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

public class SwipeDetector implements View.OnTouchListener{

    static final int MIN_DISTANCE = 100;
    private float downX, downY, upX, upY;
    public final static int RIGHT_TO_LEFT=1;
    public final static int LEFT_TO_RIGHT=2;
    public final static int TOP_TO_BOTTOM=3;
    public final static int BOTTOM_TO_TOP=4;
    private View v;

    private onSwipeEvent swipeEventListener;


    public SwipeDetector(Activity activity,View v){
        try{
            swipeEventListener=(onSwipeEvent)activity;
        }
        catch(ClassCastException e)
        {
            Log.e("ClassCastException",activity.toString()+" must implement SwipeDetector.onSwipeEvent");
        } 
        this.v=v;
    }
    public SwipeDetector(Fragment fragment,View v){
        try{
            swipeEventListener=(onSwipeEvent)fragment;
        }
        catch(ClassCastException e)
        {
            Log.e("ClassCastException",fragment.toString()+" must implement SwipeDetector.onSwipeEvent");
        } 
        this.v=v;
    }


    public void onRightToLeftSwipe(){   
        swipeEventListener.SwipeEventDetected(v,RIGHT_TO_LEFT);
    }

    public void onLeftToRightSwipe(){   
        swipeEventListener.SwipeEventDetected(v,LEFT_TO_RIGHT);
    }

    public void onTopToBottomSwipe(){   
        swipeEventListener.SwipeEventDetected(v,TOP_TO_BOTTOM);
    }

    public void onBottomToTopSwipe(){
        swipeEventListener.SwipeEventDetected(v,BOTTOM_TO_TOP);
    }

    public boolean onTouch(View v, MotionEvent event) {
        switch(event.getAction()){
        case MotionEvent.ACTION_DOWN: {
            downX = event.getX();
            downY = event.getY();
            return true;
        }
        case MotionEvent.ACTION_UP: {
            upX = event.getX();
            upY = event.getY();

            float deltaX = downX - upX;
            float deltaY = downY - upY;

            //HORIZONTAL SCROLL
            if(Math.abs(deltaX) > Math.abs(deltaY))
            {
                if(Math.abs(deltaX) > MIN_DISTANCE){
                    // left or right
                    if(deltaX < 0) 
                    {
                        this.onLeftToRightSwipe();
                        return true;
                    }
                    if(deltaX > 0) {
                        this.onRightToLeftSwipe();
                        return true; 
                    }
                }
                else {
                    //not long enough swipe...
                    return false; 
                }
            }
            //VERTICAL SCROLL
            else 
            {
                if(Math.abs(deltaY) > MIN_DISTANCE){
                    // top or down
                    if(deltaY < 0) 
                    { this.onTopToBottomSwipe();
                    return true; 
                    }
                    if(deltaY > 0)
                    { this.onBottomToTopSwipe(); 
                    return true;
                    }
                }
                else {
                    //not long enough swipe...
                    return false;
                }
            }

            return true;
        }
        }
        return false;
    }
    public interface onSwipeEvent
    {
        public void SwipeEventDetected(View v , int SwipeType);
    }

}

Answer 5

I do it a little different, and wrote an extra detector class that implements the View.onTouchListener

onCreateis simply add it to the lowest layout like this:

ActivitySwipeDetector activitySwipeDetector = new ActivitySwipeDetector(this);
lowestLayout = (RelativeLayout)this.findViewById(R.id.lowestLayout);
lowestLayout.setOnTouchListener(activitySwipeDetector);

where id.lowestLayout is the id.xxx for the view lowest in the layout hierarchy and lowestLayout is declared as a RelativeLayout

And then there is the actual activity swipe detector class:

public class ActivitySwipeDetector implements View.OnTouchListener {

static final String logTag = "ActivitySwipeDetector";
private Activity activity;
static final int MIN_DISTANCE = 100;
private float downX, downY, upX, upY;

public ActivitySwipeDetector(Activity activity){
    this.activity = activity;
}

public void onRightSwipe(){
    Log.i(logTag, "RightToLeftSwipe!");
    activity.doSomething();
}

public void onLeftSwipe(){
    Log.i(logTag, "LeftToRightSwipe!");
    activity.doSomething();
}

public void onDownSwipe(){
    Log.i(logTag, "onTopToBottomSwipe!");
    activity.doSomething();
}

public void onUpSwipe(){
    Log.i(logTag, "onBottomToTopSwipe!");
    activity.doSomething();
}

public boolean onTouch(View v, MotionEvent event) {
    switch(event.getAction()){
        case MotionEvent.ACTION_DOWN: {
            downX = event.getX();
            downY = event.getY();
            return true;
        }
        case MotionEvent.ACTION_UP: {
            upX = event.getX();
            upY = event.getY();

            float deltaX = downX - upX;
            float deltaY = downY - upY;

       // swipe horizontal?
        if(Math.abs(deltaX) > Math.abs(deltaY))
        {
            if(Math.abs(deltaX) > MIN_DISTANCE){
                // left or right
                if(deltaX > 0) { this.onRightSwipe(); return true; }
                if(deltaX < 0) { this.onLeftSwipe(); return true; }
            }
            else {
                    Log.i(logTag, "Horizontal Swipe was only " + Math.abs(deltaX) + " long, need at least " + MIN_DISTANCE);
                    return false; // We don't consume the event
            }
        }
        // swipe vertical?
        else 
        {
            if(Math.abs(deltaY) > MIN_DISTANCE){
                // top or down
                if(deltaY < 0) { this.onDownSwipe(); return true; }
                if(deltaY > 0) { this.onUpSwipe(); return true; }
            }
            else {
                    Log.i(logTag, "Vertical Swipe was only " + Math.abs(deltaX) + " long, need at least " + MIN_DISTANCE);
                    return false; // We don't consume the event
            }
        }

            return true;
        }
    }
    return false;
}

}

Works really good for me!

Answer 6

There's a built-in interface that you can use directly for all gestures:
Here is an explanation for a basic level user: There is 2 imports be careful in choosing that both are diferent