我正在尝试使用Zxing读取QR码:self.capture=[[ZXCapturealloc]init];self.capture.rotation=90.0f;//Usethebackcameraself.capture.delegate=self;self.capture.camera=self.capture.back;self.capture.layer.frame=self.view.bounds;[self.view.layeraddSublayer:self.capture.layer];我收到这个错误:*由于未捕获的异常“NSGenericException”而终止应