ios - Draw CAGradient within MKPolyLineView -

i have problem mkpolylineview. try make color gradient polyline, cagradient doenst work. subclasses mkpolylineview , redrawing in

- (void)drawmaprect:(mkmaprect)maprect zoomscale:(mkzoomscale)zoomscale incontext:(cgcontextref)context   uicolor *darker = [uicolor blackcolor];     cgfloat basewidth = self.linewidth / zoomscale;      // draw dark colour thicker     cgcontextaddpath(context, self.path);     cgcontextsetstrokecolorwithcolor(context, darker.cgcolor);     cgcontextsetlinewidth(context, basewidth * 1.5);     cgcontextsetlinecap(context, self.linecap);     cgcontextstrokepath(context);      // draw stroke color regular width     cgcontextaddpath(context, self.path);     cgcontextsetstrokecolorwithcolor(context, self.strokecolor.cgcolor);     cgcontextsetlinewidth(context, basewidth);     cgcontextsetlinecap(context, self.linecap);     cgcontextstrokepath(context);      [super drawmaprect:maprect zoomscale:zoomscale incontext:context]; } 

but not working (strokecolor = red). ideas how gradient polyline? (highcolor, centercolor, lowcolor)

thanks everyone.

to paint mkpolyline gradient, can use custom subclass of mkpolylineview. coregraphics not support stroking path gradient, have

1. convert path shape traces paths edge using cgpathcreatecopybystrokingpath
2. clip context shape
3. fill using cgcontextdrawlineargradient

here subclass started:

@interface twogradientpolylineview : mkpolylineview  @end  @implementation twogradientpolylineview  - (void)strokepath:(cgpathref)path incontext:(cgcontextref)context {     cgfloat linewidth = cgcontextconvertsizetouserspace(context, (cgsize){self.linewidth, self.linewidth}).width;     cgpathref pathtofill = cgpathcreatecopybystrokingpath(path, null, linewidth, self.linecap, self.linejoin, self.miterlimit);     cgrect rect = cgpathgetboundingbox(pathtofill);     cgcontextaddpath(context, pathtofill);     cgpathrelease(pathtofill);     cgcontextclip(context);      cgfloat gradientlocations[2] = {0.0f, 1.0f};     cgfloat gradientcolors[8] = {1.0f, 0.0f, 0.0f, 0.75f, 1.0f, 1.0f, 0.0f, 0.75f};     cgcolorspaceref colorspace = cgcolorspacecreatedevicergb();     cggradientref gradient = cggradientcreatewithcolorcomponents(colorspace, gradientcolors, gradientlocations, 2);     cgcolorspacerelease(colorspace);      cgpoint gradientstart = rect.origin;     cgpoint gradientend = {cgrectgetmaxx(rect), cgrectgetmaxy(rect)};      cgcontextdrawlineargradient(context, gradient, gradientstart, gradientend, kcggradientdrawsafterendlocation);     cggradientrelease(gradient); }  @end 

here screenshot of path drawn class above: