Beginning cocoa programming: delegates

Question

Xcode 3.2.2
Mac OS X 10.6.8
Cocoa Programming for Mac OS X (third edition)
Chapter 6: Helper objects
What happened to the forum software?  I can't quote text/code anymore.
I'm trying to create a simple delegate for an NSWindow.  The delegate implements this method:
- (NSSize)windowWillResize:(NSWindow *)sender toSize:(NSSize)frameSize;
I can get my delegate to work if I use Interface Builder to connect my app's main(and only) window to an instance of my object(which appears in the MainMenu.xib inspector in IB).  However, I cannot get a delegate to work if I call setDelegate: on my app's main window.  In the book, there is one example where they use setDelegate: to setup the delegate object.  There is another example where they use IB to hook up the delegate.  The only distinction I can detect between the two examples is that in the one that employs setDelegate:, the delegate-or is not a widget, and in the one that uses IB to make the connection, the delegate-or is a widget.
This is the code that I used to try and programmatically set up a delegate:
//AppController.h
#import <Cocoa/Cocoa.h>
@interface AppController : NSObject {
  IBOutlet NSWindow* window;
- (id)init;
@end
//AppController.m
#import "AppController.h"
#import "MyDelegate.h"
@implementation AppController
- (id)init
  if (![super init]) {
  return nil;
  MyDelegate* aDelegate = [[MyDelegate alloc] init];
  [window setDelegate:aDelegate];
  return self;
@end
//MyDelegate.h
#import <Cocoa/Cocoa.h>
@interface MyDelegate : NSObject <NSWindowDelegate> {
- (NSSize)windowWillResize:(NSWindow *)sender toSize:(NSSize)frameSize;
@end
//MyDelegate.m
#import "MyDelegate.h"
@implementation MyDelegate
- (NSSize)windowWillResize:(NSWindow *)sender
                         toSize:(NSSize)frameSize
     frameSize.height = 2 * frameSize.width;
     return frameSize;
@end
In IB, I went into the Library, and I dragged an Object to the MainMenu.xib window/inspector, and I named it AppController.  Then I dragged a connection from the AppController outlet named 'window' to the NSWindow.  When I build&run my code, I can resize the window to any size--the window size is not constrained to a 2:1 ratio. That is not the result I expect: I expect the window size to maintain a 2:1 ration. If I set an object's delegate, then when the event occurs, the object should grab the delegate and use it to call the delegation methods; there is nothing more I should have to do in my code.  What am I not understanding about cocoa delegates?

Answer 1

I constructed another simple example of a delegate: I created an app with one lone NSTextField on the window.  I wanted to see if setDelegate: would work with a different widget(NSTextField v. NSWindow).  My goal was to see if I could setup a delegate using setDelegate: on an NSTextField, such that a delegate method would be called when I typed in the text field.  I  looked through the documentation, and I decided to to see if implementing this delegate method would work:
- (BOOL)control:(NSControl *)control textShouldBeginEditing:(NSText *)fieldEditor;
I created a new app(deleting the classes that Xcode automatically creates, as well as the instance in the MainWindow.xib window in IB), and then I created this class:
//MyDelegate.h
import <Cocoa/Cocoa.h>
@interface MyDelegate : NSObject <NSTextFieldDelegate> {
- (BOOL)control:(NSControl *)control
          textShouldBeginEditing:(NSText *)fieldEditor;
@end
//MyDelegate.m
@implementation MyDelegate
- (BOOL)control:(NSControl *)control
               textShouldBeginEditing:(NSText *)fieldEditor
          NSLog(@"***In delegate method...");
          return YES;
@end
1) In IB, I created an instance of MyDelegate by dragging an Object from the Library onto the MainWindow.xib window.  I entered the name MyDelegate in the TextField Identity Inspector.
2) In IB, I ctrl-clicked on the NSTextField, and then I dragged a connection from NSTextField's 'delegate' outlet to the MyDelegate instance(in the MainWindow.xib window).
3) Saved everything, build&run, and when I typed in the text field, I saw the logged message in the Debugger Console, as expected.
Next, I attempted to create code that uses setDelegate: to achieve the same thing as above.
4) In IB, I ctrl-clicked on the NSTextField and deleted the connection from the 'delegate' outlet to the MyDelegate instance.
5)  I made these changes to the code:
//MyDelegate.h
#import <Cocoa/Cocoa.h>
@interface MyDelegate : NSObject <NSTextFieldDelegate> {
          IBOutlet NSTextField* textField;
- (id)init;
- (BOOL)control:(NSControl *)control
          textShouldBeginEditing:(NSText *)fieldEditor;
@end
//MyDelegate.m
#import "MyDelegate.h"
@implementation MyDelegate
- (id) init
          if (![super init]) {
                    return nil;
          [textField setDelegate:self];
          return self;
- (BOOL)control:(NSControl *)control
          textShouldBeginEditing:(NSText *)fieldEditor
          NSLog(@"***In delegate method...");
          return YES;
@end
6) In IB, I ctrl-clicked on the MyDelegate instance in the MainWindow.xib window, and then I dragged a connection from the outlet 'textField' to the NSTextField(in the app's main window).
7) I saved in IB, then build&run (save everything), and this time when I typed in the textfield, the message was not logged to the Debug Console.
What is the matter with setDelegate:?  Why doesn't setDelegate: succeed in setting up the delegate so that I can see the message logged to the console?
Thanks