IOS: use a gesture to calculate distance from two cgpoint

Question

I have this code for gesture in a view

- (void)rightSwipeHandle:(UIPanGestureRecognizer*)gestureRecognizer{

    CGPoint touchBegan;
    CGPoint pointEnd;

    if (gestureRecognizer.state == UIGestureRecognizerStateBegan) 
    {   
        CGPoint touchBegan = [gestureRecognizer locationInView: gestureRecognizer.view];
        NSLog(@"pointBegan:%@",NSStringFromCGPoint(touchBegan));
    }
    else if (gestureRecognizer.state == UIGestureRecognizerStateChanged)
    {
    }

    else if (gestureRecognizer.state == UIGestureRecognizerStateEnded     ||
             gestureRecognizer.state == UIGestureRecognizerStateCancelled ||
             gestureRecognizer.state == UIGestureRecognizerStateFailed)
    {   
        pointEnd = [gestureRecognizer locationInView:gestureRecognizer.view];
        NSLog(@"pointEnd:%@", NSStringFromCGPoint(pointEnd));

        CGFloat xDist = (pointEnd.x - touchBegan.x);
        CGFloat yDist = (pointEnd.y - touchBegan.y);
        CGFloat distance = sqrt((xDist * xDist) + (yDist * yDist));
        NSLog(@"distance:%f", distance);
    }


}

but it don't work fine and I don't know where is the problem... if the swipe is from the bottom to the top, it calculate a distance and if you do the opposite it calculate a big different distance, I don'tr understand

See if both pointStart and pointEnd have valid values in the last closure. — Alexander, Feb 22 '12 at 14:36
it's not normal: pointBegan:{19, 223} pointEnd:{19, 257} distance:257.701385 result must be 34 — cyclingIsBetter, Feb 22 '12 at 14:57
No, you didn't understand me. Add value printing for `touchBegan` in the line where you print `pointEnd`. — Alexander, Feb 22 '12 at 15:16

Alexander · Accepted Answer · 2012-02-22T15:39:46.680

5

Define the points as static, otherwise the touchBegan point will lose its value. It happens because setting the values of each point occurs in different method calls and with each one, you redefine the points at the beginning.

static CGPoint touchBegan;
static CGPoint pointEnd;

edited Feb 22 '12 at 15:39

answered Feb 22 '12 at 15:17

Alexander

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agree. at least for touchBegan. it's uninitialized in the else if branches. – danh Feb 22 '12 at 15:29

IOS: use a gesture to calculate distance from two cgpoint

1 Answers1