ios - Swift - Using CGContext to draw with finger -


i'm trying make drawing app. have single custom uiview:

class drawview: uiview {  var touch : uitouch! var lastpoint : cgpoint! var currentpoint : cgpoint!  override func touchesbegan(touches: set<nsobject>, withevent event: uievent) {     touch = touches.first as! uitouch     lastpoint = touch.locationinview(self)     println(lastpoint) }  override func touchesmoved(touches: set<nsobject>, withevent event: uievent) {     touch = touches.first as! uitouch     currentpoint = touch.locationinview(self)      self.setneedsdisplay()      lastpoint = currentpoint }  override func drawrect(rect: cgrect) {     var context = uigraphicsgetcurrentcontext()     cgcontextsetlinewidth(context, 5)     cgcontextsetstrokecolorwithcolor(context, uicolor.bluecolor().cgcolor)     cgcontextsetlinecap(context, kcglinecapround)      cgcontextbeginpath(context)      if lastpoint != nil {         cgcontextmovetopoint(context, lastpoint.x, lastpoint.y)         cgcontextaddlinetopoint(context, currentpoint.x, currentpoint.y)     }      cgcontextstrokepath(context) }  }

when run it, however, blue dot follows finger, no lines?

what doing wrong?

two things:

  1. calling self.setneedsdisplay doesn't call drawrect. sets flag drawrect called in near future. since set lastpoint currentpoint right after that, when drawrect called lastpoint equal currentpoint.

  2. drawrect redraws entire view every time called, @ you'd ever see recent line. if fixed problem 1, you'd have short line following finger instead of dot. if want see whole trail, you'll need store points in array property of view, , draw lines connect of points in drawrect.


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