Question

I have a class called ToolbarView which is a subclass of UIView and basically creates a UIView that has a disappearing / reappearing UIToolbar on top. I also have a subclass of ToolbarView called DraggableToolbarView enables the user to drag the view around the screen.

I need to create a delegate for ToolbarView so it can notify another object / class of when the toolbar reappears and disappears. I also need to create a delegate for DraggableToolbarView so I can notify another object / class when the view is dragged. DraggableToolbarViews delegate will also need to notify another object / class of when the toolbar reappears and disappears.

So I decided to implement ToolbarViewDelegate, and have DraggableToolbarViewDelegate inherit from it and have its own method like following:

ToolbarView.h

#import <UIKit/UIKit.h>

@protocol ToolbarViewDelegate;

@interface ToolbarView : UIView <UIGestureRecognizerDelegate>
{
    id <ToolbarViewDelegate> _toolbarViewDelegate;
}

@property(nonatomic, assign) id <ToolbarViewDelegate> toolbarViewDelegate;

@end

ToolbarView.m

#import "ToolbarView.h"
#import "ToolbarViewDelegate.h"

...

- (void) showBars
{      
       ...
        if (self.toolbarViewDelegate)
        {
            [self.toolbarViewDelegate toolbarViewWillShowToolbar:self];
        }

       ...
}

- (void) hideBars
{
       ...
        if (self.toolbarViewDelegate)
        {
            [self.toolbarViewDelegate toolbarViewWillHideToolbar:self];
        }

        ...
}

ToolbarViewDelegate.h

@class ToolbarView;

@protocol ToolbarViewDelegate

@required

- (void) toolBarViewWillShowToolbar:(ToolbarView *)toolbarView;
- (void) toolBarViewWillHideToolbar:(ToolbarView *)toolbarView;

@end

DraggableToolbarView.h

#import “ToolbarView.h”

@protocol DraggableToolbarViewDelegate;

@interface DraggableToolbarView : ToolbarView
{
    id <DraggableToolbarViewDelegate> _draggableToolbarViewDelegate;
}

@property(nonatomic, assign) id <DraggableToolbarViewDelegate> draggableToolbarViewDelegate;

@end

DraggableToolbarView.m

#import "DraggableToolbarView.h"
#import "DraggableToolbarViewDelegate.h"

...

- (void)drag:(UIPanGestureRecognizer *)sender
{
   ...
        if (self.draggableToolbarViewDelegate)
        {
            [self.draggableToolbarViewDelegate draggableToolbarViewWillDrag:self];
        }

  ...

}

...

DraggableToolbarViewDelegate.h

#import "ToolbarViewDelegate.h"

@class DraggableToolbarView;

@protocol DraggableToolbarViewDelegate <ToolbarViewDelegate>

@required

- (void) draggableToolbarViewWillDrag:(DraggableToolbarView *)draggableToolbarView;

@end

SomeViewController.h

#import <UIKit/UIKit.h>
#import "ToolbarViewDelegate.h"
#import "DraggableToolbarViewDelegate.h"

@interface SomeViewController : UIViewController <ToolbarViewDelegate, DraggableToolbarViewDelegate>
{

}
@end

SomeViewController.m

#import "DraggableToolbarView.h"
...
- (void) toolbarViewWillShowToolbar:(ToolbarView*)toolbarView
{
    //NSLog(@"Toolbar Showed");
}

- (void) toolbarViewWillHideToolbar:(ToolbarView*)toolbarView
{
    //NSLog(@"Toolbar Hidden");
}

- (void) draggableToolbarViewWillDrag:(DraggableToolbarView*)draggableToolbarView
{
    //NSLog(@"Dragged");
}

...

[draggableToolbarView setDraggableToolbarViewDelegate:self];

...

When I do this only the DraggableToolbarDelegate methods are responding. However when I also do [drabbleToolbarView setToolbarViewDelegate:self] it works. I’ve tried doing each delegate separately without inheritence and it works fine so I believe the problem isn’t in any other part of the code.

Anyone might know why? I figured by making the protocols inherit, I wouldn’t also have to set the ToolbarViewDelegate for a DraggableToolbar object.

UPDATE: Added a lot more code

Answer 1

In your code, any given DraggableToolbarView instance has two properties to connect to delegates, one called toolbarViewDelegate which it inherits from its superclass, and one called draggableToolbarViewDelegate which is defined in DraggableToolbarView itself. You’ve got to set both of those if you want the controller to get all the delegate messages.

What you’re trying to do is possible, however. You need to use the same property name in both your view classes, so that there is only one delegate connection for any instance.

First, change the name of the delegate in the superclass. (Note that you don’t need, and indeed shouldn’t bother, to declare an ivar for the property — it’s created by @synthesize.)

@interface ToolbarView : UIView <UIGestureRecognizerDelegate>
@property (nonatomic, assign) id <ToolbarViewDelegate> delegate;
@end

You will use the same property name in the subclass.

@interface DraggableToolbarView : ToolbarView
@property (nonatomic, assign) id <DraggableToolbarViewDelegate> delegate;
@end

This is allowed as long as the name of the backing ivar in the subclass is different than that of the superclass, e.g.,

// In superclass
@synthesize delegate;
// In subclass
@synthesize delegate = delegate_;

Now change all the delegate messages in the two view classes to use this one property:

- (void)showBars 
{

    if (self.delegate)
    {
        [self.delegate ...

- (void)drag:(UIPanGestureRecognizer *)sender
{
    //...
    if (self.delegate)
    {
        [self.delegate ...

Now you can send setDelegate: to a DraggableToolbarView and it will use the same delegate for the dragging methods and the show/hide methods.

Finally, a terminology/explanatory note. In response to your previous question, Caleb used the correct term for “stacked” protocols, and Richard did not. Protocols don’t inherit from each other, but one protocol can adopt the other. The relationship is similar, but distinct. When an object conforms to a protocol, it promises to implement the methods declared in that protocol. No implementation comes along with the protocol. The same is true of one protocol adopting the other — the methods are just declared to exist in both. When you write:

@protocol DraggableToolbarViewDelegate <ToolbarViewDelegate>

you are saying that any object which promises to implement DraggableToolbarViewDelegate‘s methods will also implement the methods from ToolbarViewDelegate. That’s all that it means. Again, no implementation comes along with that promise.

In this case, that means that a DraggableToolbarView can expect its delegate to implement the methods in ToolbarViewDelegate.