using touchesbegan and touchesmoved to distinguish flick and drag

Question

i use these two functions to detect the user slowly drag and drop on uiview

-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event

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

however, how can i use these two methods to detect user actually flick(quick flip) uiview ?

how can i distinguish flick from drag?

thanks a lot for your help!

justicepenny

Daniel G. Wilson Daniel G. Wilson · Accepted Answer · 2013-01-09T00:46:01

Drag and Flick are usually distinguished by speed - one solution would be to create an algorithm based on the distance formula.

One rough example:

CGPoint pointOld = CGPointMake(0, 0); // Not sure if this is valid
CGPoint pointNew = CGPointMate(0, 0); // Just making holders for the
                                      // location of the current and previous touches

float timeInterval = 0.2f;
// However long you think it will take to have enough of a difference in
// distance to distinguish a flick from a drag

float minFlickDist = 100.0f;
// Minimum distance traveled in timeInterval to be considered a flick

- (void)callMeEveryTimeInterval
{
    // Distance formula
    float distBtwnPoints = sqrt( (pointNew.x - pointOld.x) * (pointNew.x - pointOld.x) - (pointNew.y - pointOld.y) * (pointNew.y - pointOld.y) );
    if (distBtwnPoints >= minFlickDist)
    {
        // Flick
    } else {
        // Drag
    }
}

Really rough sketch of something I think might work - hope that helps.

using touchesbegan and touchesmoved to distinguish flick and drag

3 Answers