ios - UIGestureRecognizerStateChangedv called twice when moving bezier image in a subView -

i implemented square draw using uibezierpath. in order move same square, implemented uilongpressgesturerecognizer can check if square pressed , move square freely in subview.

here of code:

square.h  ... //square coordinates , size  static const float xpoint = 10; static const float ypoint = 16; static const float width = 10; static const float height = 20;  //bezier bitmap context static const float contextwidht = 300; static const float contextheigh = 300; ...   square.m ... -(void)build{    uibezierpath *squaredraw = [uibezierpath bezierpathwithrect:cgrectmake(xpoint, ypoint, width, height)];   uigraphicsbeginimagecontext(cgsizemake(contextwidht, contextheigh));    // graphic context   cgcontextref context = uigraphicsgetcurrentcontext();   cgcontextsetstrokecolorwithcolor(context, [uicolor bluecolor].cgcolor);   cgcontextsetfillcolorwithcolor(context, [uicolor clearcolor].cgcolor);    [squaredraw fill];   [squaredraw stroke];    // image graphic context   uiimage *bezierimage = uigraphicsgetimagefromcurrentimagecontext();   uigraphicsendimagecontext();   uiimageview *bezierimageview = [[uiimageview alloc]initwithimage:bezierimage];    //subview    _frame = bezierimageview;   [_frame setuserinteractionenabled:yes];    //gesture recognizer   uilongpressgesturerecognizer *tapgesture = [[uilongpressgesturerecognizer alloc] initwithtarget:self action:@selector(taphandler:)];   tapgesture.delegate = (id)self;    [_frame addgesturerecognizer:tapgesture];   [self addsubview:_frame];  }  - (void)taphandler:(uilongpressgesturerecognizer *) sender{    sender.delegate = (id)_frame;   cgpoint touchlocation = [sender locationinview:_frame];   cgfloat xvariation, yvariation;   ...    case uigesturerecognizerstatechanged:     xvariation = [sender locationinview:_frame].x;     yvariation = [sender locationinview:_frame].y;     _frame.center = cgpointmake(xvariation, yvariation);           break;   .... } 

seems like, when debugging app ( press , move _frame ), "uigesturerecognizerstatechanged" called twice , returning alternated points between subview , points result contextwidth , contextheight:

2013-07-22 14:55:00.327 bezier[10847:11603] xvariation: 22.000000 2013-07-22 14:55:00.329 bezier[10847:11603] yvariation: 28.000000 2013-07-22 14:55:00.330 bezier[10847:11603] xvariation: 150.000000 ----> ?? 2013-07-22 14:55:00.330 bezier[10847:11603] yvariation: 150.000000 ----> ?? 2013-07-22 14:55:00.332 bezier[10847:11603] xvariation: 29.000000 2013-07-22 14:55:00.332 bezier[10847:11603] yvariation: 28.000000 

why so?

uilongpressgesturerecognizer sends data continuously. if want 1 signal need handle in delegate , watch state. documentation:

long-press gestures continuous. gesture begins (uigesturerecognizerstatebegan) when number of allowable fingers (numberoftouchesrequired) have been pressed specified period (minimumpressduration) , touches not move beyond allowable range of movement (allowablemovement). gesture recognizer transitions change state whenever finger moves, , ends (uigesturerecognizerstateended) when of fingers lifted.