ios - How to draw a triangle over a UIImage in a UIImageView -

i'm having trouble drawing atop image in uiimageview, i've looked @ "draw image on uiimage" help. here's scenario: have uipopovercontroller uitableview in , want display triangle pointing when user @ bottom of scrollable table view.

my code:

- (uiimage *) drawtriangleinviewforsize:(cgsize)sizeofview                      imagetodrawon:(uiimage *)underimage                            isattop:(bool)top{ cgpoint firstpoint; cgpoint secondpoint; cgpoint thirdpoint;  if(!top){  //i want draw equilateral triangle (side length 10) in center of image in  //the imageview, these coordinates using.     firstpoint = cgpointmake(underimage.size.width * 0.5 + 5, underimage.size.height * 0.5 - 5);     secondpoint = cgpointmake((firstpoint.x - 10), firstpoint.y);     thirdpoint = cgpointmake(underimage.size.width * 0.5,                              underimage.size.width * 0.5 + 5);  } */ **disregard** else{     firstpoint = cgpointmake(sizeofview.width * 0.5 + 5,                              self.tableviewchoices.rowheight * 0.5 - 5);     secondpoint = cgpointmake((firstpoint.x - 10), firstpoint.y);     thirdpoint = cgpointmake(sizeofview.width * 0.5,                              self.tableviewchoices.rowheight * 0.5 + 5); }*/ //get size of image drawinrect: method cgfloat imageviewwidth = sizeofview.width; cgfloat imageviewheight = self.tableviewchoices.rowheight;  //set graphics context size of image uigraphicsbeginimagecontextwithoptions(underimage.size, yes, 0.0);  [underimage drawinrect:cgrectmake(0.0, 0.0, imageviewwidth, imageviewheight)];  //set line attributes cgcontextref ctx = uigraphicsgetcurrentcontext(); cgcontextsetstrokecolorwithcolor(ctx, [uicolor blackcolor].cgcolor); cgcontextsetfillcolorwithcolor(ctx, [uicolor clearcolor].cgcolor); cgcontextsetlinewidth(ctx, 0.05);  uigraphicspushcontext(ctx);     //draw triangle cgcontextbeginpath(ctx); cgcontextmovetopoint(ctx, firstpoint.x, firstpoint.y); cgcontextaddlinetopoint(ctx, secondpoint.x, secondpoint.y); cgcontextaddlinetopoint(ctx, thirdpoint.x, thirdpoint.y); cgcontextaddlinetopoint(ctx, firstpoint.x, firstpoint.y); cgcontextclosepath(ctx);  uigraphicspopcontext();  //get image uiimage *rslt = uigraphicsgetimagefromcurrentimagecontext(); uigraphicsendimagecontext();  return rslt; } 

i can't quite seem draw triangle uiimage in imageview, end result either black imageview (the uiimage white.png), or 1 line @ top of imageview (depending on whether use drawinrect: or drawatpoint: , coordinates use). need draw triangle pointing up, not hard thing, , looks i'm doing "by book."

your code looks complicated kind of task. why don't use simple uiimageview triangle image ever want? show when table @ bottom , that's all.

note, when you're implementing delegate uitableview you're able catch it's uiscrollview's delegate messages such scrollview:didenddecelerating: , on.

regarding code you've missed actual path draw:

cgcontextaddpath(context, trianglepath); cgcontextfillpath(context); 

to make possible should use path-related functions. using cgcontext-related functions seems improper since such approach may remove old path. better way create own mutable path in context, draw triangle in , draw path context functions mentioned above.