I want To track The Speed Of the fingure movement in pixel Per Second Is It Possible Any WaY?

Question

I want to track The speed Of the Touch moved in pixel /Second
Any Budy Having idea For This

Except the PanGesture Method

Answer 1

I'll assume you want to know the velocity between consecutive movements, and not an average over a series of movements. The theory should be easy enough to adapt if you have other requirements, though.

You will need to know three things:

1. Where is the touch now?
2. Where was the touch previously?
3. How much time has passed since then?

Then just use Pythagoras to get your distance, and divide by time for speed.

When you get a touchesMoved event, it will provide the current and previous position for you. All you need to then add is a measure of time.

For that, you will want an NSDate property in your class to help calculate the time interval. You could initialise and release it in viewDidLoad / viewDidUnload, or somewhere similar. In my example, mine is called lastTouchTime, it is retained, and I initialised like this:

self.lastTouchTime = [NSDate date];

and I release it in the predictable way.

Your touchesMoved event should then look something like this:

- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{       

    NSArray *touchesArray = [touches allObjects];
    UITouch *touch;
    CGPoint ptTouch;
    CGPoint ptPrevious;

    NSDate *now = [[NSDate alloc] init];
    NSTimeInterval interval = [now timeIntervalSinceDate:lastTouchTime];
    [lastTouchTime release];
    lastTouchTime = [[NSDate alloc] init];
    [now release];

    touch = [touchesArray objectAtIndex:0];
    ptTouch = [touch locationInView:self.view];
    ptPrevious = [touch previousLocationInView:self.view];

    CGFloat xMove = ptTouch.x - ptPrevious.x;
    CGFloat yMove = ptTouch.y - ptPrevious.y;
    CGFloat distance = sqrt ((xMove * xMove) + (yMove * yMove));

    NSLog (@"TimeInterval:%f", interval);
    NSLog (@"Move:%5.2f, %5.2f", xMove, yMove);
    NSLog (@"Distance:%5.2f", distance);
    NSLog (@"Speed:%5.2f", distance / interval);
}

Apologies if I've made a faux pas with any memory management, I'm still not very comfortable with ObjectiveC's way of doing things. I'm sure somebody can correct it if necessary!

Good luck, Freezing.