Objective-C class unable to respond to helper method - objective-c

Question

I am receiving the familiar and nonspecific diagnostic: "No visible #interface for... declares the selector ..." I appreciate that this diagnostic has appeared numerous times on this site (I have looked at most of them), but none of the suggested fixes seem to be relevant to my case. Thanks!
I have an old Cocoa program which rotates an OpenGL surface using the mouse. (It is based upon an old Apple demo: NSGL Teapot). The surface is created in an NSOpenGLView (Class SurfaceView) and the code used to perform the rotation is in a helper class called Trackball. When the mouse "slides" on the screen, a method (called rollTo) in a Trackball instance invokes a method (called rotateBy) in SurfaceView which provides the amount of rotation. Unfortunately, Xcode 7.3 complains that NSOpenGLView lacks a visible interface for the rotateBy selector (method).
The code compiled perfectly 15 years ago, but not now. Everything else in the program works fine (i.e., the surface is rendered and it responds correctly to various sliders, etc.) Can you suggest how I can get the OpenGL view to respond to rotateBy?
Thanks very much!
Here is the Interface (indented 4 spaces)
#import <Cocoa/Cocoa.h>
#import <OpenGL/OpenGL.h>
#import <OpenGL/gl.h>
#import <OpenGL/glu.h>
#import <GLUT/glut.h>
#import "Trackball.h"
#interface SurfaceView : NSOpenGLView
{
float width;
GLUnurbsObj *theNurb;
Trackball *m_trackball;
// The main rotation
float m_rotation[4];
// The trackball rotation
float m_tbRot[4];
}
- (id)initWithFrame:(NSRect)frameRect;
- (void)drawRect:(NSRect)rect;
- (void)rotateBy:(float *)r;
- (void)mouseDown:(NSEvent *)theEvent;
- (void)mouseUp:(NSEvent *)theEvent;
- (void)mouseDragged:(NSEvent *)theEvent;
- (void)zeroRotate;
#end
Method body:
- (void)rotateBy:(float *)r
{
m_tbRot[0] = r[0];
m_tbRot[1] = r[1];
m_tbRot[2] = r[2];
m_tbRot[3]= r[3];
}
Here is the method in which the error occurs:
- (void)rollTo:(NSPoint)pt sender:(NSOpenGLView *)sender
{
float xxyy;
float rot[4];
float cosAng, sinAng;
float ls, le, lr;
m_endPt[0] = pt.x - m_ctr.x;
m_endPt[1] = pt.y - m_ctr.y;
if (fabs(m_endPt[0] - m_startPt[0]) < kTol && fabs(m_endPt[1] - m_startPt[1]) < kTol)
return; // Not enough change in the vectors to have an action.
// Compute the ending vector from the surface of the ball to its center.
xxyy = m_endPt[0]*m_endPt[0] + m_endPt[1]*m_endPt[1];
if (xxyy > m_radius*m_radius) {
// Outside the sphere.
m_endPt[2] = 0.;
} else
m_endPt[2] = sqrt(m_radius*m_radius - xxyy);
// Take the cross product of the two vectors. r = s X e
rot[1] = m_startPt[1] * m_endPt[2] - m_startPt[2] * m_endPt[1];
rot[2] = -m_startPt[0] * m_endPt[2] + m_startPt[2] * m_endPt[0];
rot[3] = m_startPt[0] * m_endPt[1] - m_startPt[1] * m_endPt[0];
// Use atan for a better angle. If you use only cos or sin, you only get
// half the possible angles, and you can end up with rotations that flip around near
// the poles.
// cos(a) = (s . e) / (||s|| ||e||)
cosAng = m_startPt[0]*m_endPt[0] + m_startPt[1]*m_endPt[1] + m_startPt[2]*m_endPt[2]; // (s . e)
ls = sqrt(m_startPt[0]*m_startPt[0] + m_startPt[1]*m_startPt[1] + m_startPt[2]*m_startPt[2]);
ls = 1. / ls; // 1 / ||s||
le = sqrt(m_endPt[0]*m_endPt[0] + m_endPt[1]*m_endPt[1] + m_endPt[2]*m_endPt[2]);
le = 1. / le; // 1 / ||e||
cosAng = cosAng * ls * le;
// sin(a) = ||(s X e)|| / (||s|| ||e||)
sinAng = lr = sqrt(rot[1]*rot[1] + rot[2]*rot[2] + rot[3]*rot[3]); // ||(s X e)||;
// keep this length in lr for normalizing the rotation vector later.
sinAng = sinAng * ls * le;
rot[0] = (float)atan2(sinAng, cosAng) * kRad2Deg; // GL rotations are in degrees.
// Normalize the rotation axis.
lr = 1. / lr;
rot[1] *= lr; rot[2] *= lr; rot[3] *= lr;
[sender rotateBy:rot];
}

Answer 1

If you want to call rotateBy: on sender then your method signature needs to have a sender that implements that method.
Rewrite it as:
- (void)rollTo:(NSPoint)pt sender:(SurfaceView *)sender
You could also use a cast on sender but that's more dangerous. (i.e. likely to get a run-time error instead of a compiler one.)

Answer 2

The usage is wrong. It was probably always wrong, only the compiler is now detecting it better.
Your sender is declared as NSOpenGLView and you are calling rotateBy: method on it. NSOpenGLView does not have any such method. It's the subclass SurfaceView that has the method.
One simple fix is to declare sender as id, to completely remove type information.
A better fix is to declare the sender parameter correctly as SurfaceView.
If you need to keep the same interface, just perform a cast
[(SurfaceView *) sender rotateBy:rot];