objective c - how to get _CAEAGLNativeWindow from iOS class "CAEAGLLayer" -

objective c - how to get _CAEAGLNativeWindow from iOS class "CAEAGLLayer" -

i tried opengl es native window (_win) class:

@interface caeagllayer : calayer <eagldrawable> { @private struct _caeaglnativewindow *_win; }

so extended category:

@interface caeagllayer(mylayer) - (void*) fetchwin; @end @implementation caeagllayer(mylayer) - (void*) fetchwin { homecoming self->_win; } @end

and utilize in class:

@implementation myclass - (void)setuplayer { _eagllayer = (caeagllayer*)self.layer; _eagllayer.opaque = yes; nslog(@"_eagllayer _win: %p", [_eagllayer fetchwin]); } @end

but when building, met link error:

undefined symbols architecture x86_64: "_objc_ivar_$_caeagllayer._win", referenced from: -[caeagllayer(mylayer) fetchwin] in openglview.o ld: symbol(s) not found architecture x86_64 clang: error: linker command failed exit code 1 (use -v see invocation)

the linker can't find symbol because, default, "ivar symbols @private , @package ivars are not exported." can't access _win straight name in manner, if have header refers it.

however, can dive objc runtime , pull out instance variables. in case, might seek in -setuplayer (after #importing <objc/objc-runtime.h>):

ivar winivar = class_getinstancevariable([caeagllayer class], "_win"); void * winptr = (__bridge void *)object_getivar(_eagllayer, winivar);

(you may able utilize simple -valueforkey: on layer using @"_win" name of key, prefer runtime methods because read clearer you're trying do, circumvent intended abstraction.)

ios objective-c