Delegation - creating your own delegate

Delegation is a way to have an unrelated class (object) perform methods for another class (object).  A delegate is a protocol, and you declare the delegate in the class that you want it to operate on.  The following example shows all of the code details for building your own custom delegate.  Many delegates come prepackaged in iOS and you implement them in a similar way shown below this example.

You declare a delegate in the class header file either above or below the @interface code.  You give it a name & list the methods that it can perform.  The methods can either be optional or required.  Required is the default.   The (float)smileForFaceView: is a required method that must be implemented by whoever declares themselves conforming to the delegate. NOTE; that we send a copy of ourself (FaceView) along with the method.  This allows the other object to look at the FaceView object.
in FaceView.h -
@protocol FaceViewDataSource
- (float)smileForFaceView:(FaceView *)sender;
@end

@interface FaceView : UIView

then in a class that you want to conform to the delegate, you add the following to it's @interface line.
in HappinessViewController.m - (for a private delegation??)

 @interface HappinessViewController()

or in HappinessViewCntroller.m - (more common way to do)

  @interface HappinessViewController

 We next need to declare ourselves as the delegate like;

in FaceView.h - (?? declares a property of FaceView.  This allows the conforming class to ??

@property (nonatomic, weak) IBOutlet id dataSource;

We then also need to declare the new class as the delegate??

in HappinessViewController.m - the method - - (void)setFaceView:(FaceView *)faceView

self.faceView.dataSource = self;

Now the final thing to do is just implement the required methods of this delegate in the conforming class (HappinessViewController).  We then implement smileForFaceView like;

in HappinessViewController.m - 

- (float)smileForFaceView:(FaceView *)sender   // this just convert the happiness property to +/- 1
{
    return (self.happiness - 50) / 50.0;
}

And finally ??????;

in FaceView.m, the - draawRect method - 

    float smile = [self.dataSource smileForFaceView:self]; // delegate our View's data

 See the next Post for implementing canned delegates;

 (as always many thanks to the incomparable Paul Hegerty and his Stanford iOS lectures