ios - CGContext invalid context 0x0 -

i drawing cglayers, creating layer , drawing layer graphics context in drawrect method, way

- (void)drawrect:(cgrect)rect {                    cgcontextref context = uigraphicsgetcurrentcontext();      if(self.currentdrawinglayer == nil)      {          cglayerref layer = cglayercreatewithcontext(context, bounds.size, null);              self.currentdrawinglayer = layer;      }                         cgcontextdrawlayerinrect(context, self.bounds, self.currentdrawinglayer);         } 

i drawing operations in touchesmoved function

-(void)touchesmoved:(nsset *)touches withevent:(uievent *)event {       cgcontextref layercontext =  cglayergetcontext(self.currentdrawinglayer);        cgcontextsetlinecap(layercontext, kcglinecapround);       cgcontextsetlinejoin(layercontext, kcglinejoinround);       cgcontextsetallowsantialiasing(layercontext, yes);       cgcontextsetshouldantialias(layercontext, yes);       cgcontextsetblendmode(layercontext,kcgblendmodeclear);       cgcontextsetlinewidth(layercontext, self.erasewidth);       cgcontextbeginpath(layercontext);       cgcontextaddpath(layercontext, mutablepath);       cgcontextstrokepath(layercontext);       cgpathrelease(mutablepath);        [self setneedsdisplay]; } 

but when start drawing, error messages cgcontext functions used in touches moved, of listing few below.

<error>: cgcontextbeginpath:   serious error. application, or library uses, using invalid context  , thereby contributing overall degradation of system stability , reliability. notice courtesy: please fix problem. become fatal error in upcoming update. <error>: cgcontextaddpath: invalid context 0x0. serious error. application, or library uses, using invalid context  , thereby contributing overall degradation of system stability , reliability. notice courtesy: please fix problem. become fatal error in upcoming update. 

1. i know error because, layer not created yet, , because of that, error, layer should created in drawrect method because, graphics context alive.
2. if call [self setneedsdisplay]first , drawing functions, , again @ last [self setneedsdisplay], works fine, no errors, dont think, or rather dont know wheteher right thing do.

in -touchesmoved:withevent: method, return if don’t have layer yet. user can’t draw if can’t see view, after all. i.e. add

 if (!self.currentdrawinglayer)    return; 

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