# How to capture finger movement direction in android phone?-ThrowExceptions

Exception or error:

I want to capture the finger movement direction on Android touch phone. If a user slides his finger in up/down/left/right direction, I want to capture this direction. How can I find this? Thanks.

How to solve:

Implement onTouchEvent(), and calculate dx and dy by where the user presses down and lifts up. You can use these values to figure out the direction of the move.

``````float x1, x2, y1, y2, dx, dy;
String direction;
switch(event.getAction()) {
case(MotionEvent.ACTION_DOWN):
x1 = event.getX();
y1 = event.getY();
break;

case(MotionEvent.ACTION_UP): {
x2 = event.getX();
y2 = event.getY();
dx = x2-x1;
dy = y2-y1;

// Use dx and dy to determine the direction of the move
if(Math.abs(dx) > Math.abs(dy)) {
if(dx>0)
direction = "right";
else
direction = "left";
} else {
if(dy>0)
direction = "down";
else
direction = "up";
}
}
}
``````

###

Your best bet would be to deal with the MotionEvent’s you get from a View.OnTouchListener() callback. The motion events keep track of how you are currently interacting with the View by its action property.

I would imagine you can calculate which direction someone slides their finger by examining the action property of the MotionEvents and the x/y values of where the motion event took place.

``````switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
oldX= event.getX();
oldY= event.getY();
break;
case MotionEvent.ACTION_MOVE:
int newX = motionEvent.getX();
int newY = motionEvent.getY();

int deltaX = oldX - newX;
int deltaY = oldY - newY;

if(Math.abs(deltaY)>Math.abs(deltaX))
//Motion in Y direction.
else
// Motion in X direction.
break;
}
``````

There are lots of other method available on the MotionEvent object for use as well:
http://developer.android.com/reference/android/view/MotionEvent.html

###

I think instead of having bunch of variables better to use VelocityTracker

Here is modified example from Developer Android

``````private var mVelocityTracker: VelocityTracker? = null

override fun onTouchEvent(event: MotionEvent): Boolean {

MotionEvent.ACTION_DOWN -> {
// Reset the velocity tracker back to its initial state.
mVelocityTracker?.clear()
// If necessary retrieve a new VelocityTracker object to watch the
// velocity of a motion.
mVelocityTracker = mVelocityTracker ?: VelocityTracker.obtain()
// Add a user's movement to the tracker.
}
MotionEvent.ACTION_MOVE -> {
mVelocityTracker?.run {
val pointerId: Int = event.getPointerId(event.actionIndex)
// When you want to determine the velocity, call
// computeCurrentVelocity(). Then call getXVelocity()
// and getYVelocity() to retrieve the velocity for each pointer ID.
computeCurrentVelocity(1000)

val xVelocity = getXVelocity(pointerId)
val yVelocity = getYVelocity(pointerId)

if (abs(xVelocity) > abs(yVelocity))
if (xVelocity > 0)
// right
else
// left
else
if (yVelocity > 0)
// down
else
// up
}
}
MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {
// Return a VelocityTracker object back to be re-used by others.
mVelocityTracker?.recycle()
mVelocityTracker = null
}
}
return true
}
``````