Using delegate to pass data between views

Question

I am building a utility application which shares data between main view and flip view. Actually, it is not exactly the flip view that's holding data, it's the custom view that's an instance of the flip view when it gets loaded. I have explained the specifics in my previous thread here, but I haven't got a solution yet. And I have redeveloped my code, hopefully this time I could make myself clear.

The general concept here is I create and store data in my main view, and pass it to the flip side view using the predefined delegate in the FlipViewController. Then in the FlipViewController, I store the data in my own delegate and pass it to the custom view which implements my own delegate method. The following is the main portions of the code.

MainViewController.m (only adopts <FlipsideViewControllerDelegate> protocol)

- (IBAction)showInfo:(id)sender {    

    FlipsideViewController *controller = [[FlipsideViewController alloc] initWithNibName:@"FlipsideView" bundle:nil];
    controller.delegate = self;

    controller.chart = data;

    controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
    [self presentModalViewController:controller animated:YES];

    [controller release];
}

FlipsideViewController.h

@protocol FlipsideViewControllerDelegate;
@protocol ChartDelegate;

@interface FlipsideViewController : UIViewController {
    id <FlipsideViewControllerDelegate> delegate;
    id <ChartDelegate> delegate2;
    DataModel *chart;
}

@property (nonatomic, assign) id <FlipsideViewControllerDelegate> delegate;
@property (nonatomic, assign) id <ChartDelegate> delegate2;
@property (nonatomic, retain) DataModel *chart;
- (IBAction)done:(id)sender;
@end


@protocol FlipsideViewControllerDelegate
- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller;
@end

@protocol ChartDelegate <NSObject>
- (void)getParams:(DataModel *)dataModel;
@end

FlipsideViewController.m

@synthesize delegate, delegate2;
@synthesize chart;

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor viewFlipsideBackgroundColor]; 
        if ([delegate2 respondsToSelector:@selector(getParams:)]) {
        [delegate2 getParams:chart];
    }
}

customDrawing.h

@interface customDrawing : UIView <ChartDelegate>{
    DataModel *chartData;
}
@property (nonatomic, retain) DataModel *chartData;
@end

customDrawing.m

@synthesize chartData;
-(void)getParams:(DataModel *)dataModel{
        chartData = dataModel;
}

It turns out the data didn't get passed to the chartData object in my custom view. HELP?

Why not abstract the model out from your view and have both views observing the model? Views shouldn't be storing data... — Stephen, Aug 21 '11 at 17:00

score 5 · Accepted Answer · answered Aug 21 '11 at 17:31

You are missing the fundamentals. I do not think you need delegates to achieve this task but here we go.

A protocol is like a contract. In you FlipsideViewController class you defined the protocol which essentially states if you conform to this protocol then you must implement this method.

How do you conform to a protocol?

In MainViewController the @interface will look something like this

@interface MainViewController : UIViewController <FlipsideViewControllerDelegate>

The fact that you have the protocol written in angled brackets means that you promise to conform to the protocol and therefore have to implement

 - (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller;

in your MainViewController.m.

Now when MainNavigationController set's itself as the delegate (controller.delegate = self;) it finishes the link. This allows the FlipsideViewController to call

[delegate flipsideViewControllerDidFinish:self];

Which will call the method defined in MainViewController which dismisses the modal view controller.

You have defined a second protocol (you could have added the method to the first and then you would not have to adopt two protocols) and as others have pointed out you have not linked the classes up by doing

controller.delegate2 = self;

This would not solve your problem. You would still need to conform to the ChartDelegate by adding it to the declaration. Once you have done that you will still not be out of the water because the method is not correct.

Full solution - not using delegates as they are not really required here

MainViewController.h

@interface MainViewController : UIViewController <FlipsideViewControllerDelegate>

- (IBAction)showInfo:(id)sender;

@end

MainViewController.m

@implementation MainViewController

- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller
{
    [self dismissModalViewControllerAnimated:YES];
}

- (IBAction)showInfo:(id)sender
{    
    FlipsideViewController *controller = [[FlipsideViewController alloc] initWithNibName:@"FlipsideView" bundle:nil];
    controller.delegate = self;

    /*
     * The labelText property is defined in the header for FlipsideViewController
     * In this case this is the easiest way to get data from this controller to
     * the controller we are about to display
     */
    controller.labelText = @"WHAT EVER YOU WANT TO SEND"; // <---- sending data

    controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
    [self presentModalViewController:controller animated:YES];

    [controller release];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

@end

FlipsideViewController.h

@class FlipsideViewController;

@protocol FlipsideViewControllerDelegate
- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller;
@end

@interface FlipsideViewController : UIViewController


/*
 * These properties have been added. The label is used for displaying the text
 * and needs to be hooked up in Interface builder
 *
 * The NSString is the property that is holding the data passed from MainViewController
 */
@property (nonatomic, retain) IBOutlet UILabel *testLabel;
@property (nonatomic, copy) NSString *labelText; from MainViewControlller

@property (nonatomic, assign) id <FlipsideViewControllerDelegate> delegate;

- (IBAction)done:(id)sender;

@end

FlipsideViewController.m

@implementation FlipsideViewController

@synthesize delegate = _delegate;

/*
 * We need to synthesise out properties so we get our getters and setters created
 */
@synthesize testLabel = _testLabel;
@synthesize labelText = _labelText;

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];

    /*
     * This is called once the view is set up and all connections have been made in 
     * interface builder. Therefore we can now set the text of our test label
     */
    self.testLabel.text = labelText;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

#pragma mark - Actions

- (IBAction)done:(id)sender
{
    [self.delegate flipsideViewControllerDidFinish:self];
}

- (void)dealloc
{
    /*
     * Memory management for the ivars we added
     */
    [_testLabel release];
    [_labelText release];
    [super dealloc];
}

@end

Your solution seems to get the data to the flipsideview, as I said before that's not what i need to do. I need to do a custom drawing on a subview that's on top of the flipsideview using the data passed from the mainview. And that's why I pass the "chart" to delegate2 in the viewDidLoad method as soon as the flipsideview gets loaded. — Michael, Aug 22 '11 at 03:42
Thanks! I have worked it out. I forgot to instantiate an object in my flipsideviewcontroller, now I only need to pass data to that subview object directly. — Michael, Aug 22 '11 at 05:51

score 0 · Answer 2 · answered Aug 21 '11 at 16:55

0

You have two properties: delegate and delegate2. You are assigning a value to delegate, but calling the method on delegate2 later.

answered Aug 21 '11 at 16:55

Nathanial Woolls

5,231
24
32

score 0 · Answer 3 · answered Aug 21 '11 at 16:59

0

You need to assign the delegate2 (your customDrawing class). You are only assigning the delegate.

answered Aug 21 '11 at 16:59

Mundi

79,884
17
117
140

Do you mean I need controller.delegate2 = self; in my mainviewcontroller.m? That would mean I have to adopt together with in the mainviewcontroller? – Michael Aug 21 '11 at 17:02
You need to assign whatever class is the `delegate2`, i.e. that holds the implementation that handles the methods. Perhaps the main view controller is a good place. – Mundi Aug 21 '11 at 17:33
I assigned delegate2 in a method in my customDrawing class like this: ChartDelegate *chartDelegate = [[ChartDelegate alloc] initWithNibName:@"FlipsideView" bundle:nil]; chartDelegate.delegate2 = self; But there is an error says "ChartDelegate" undeclared...what did I miss? I checked the showInfo() in mainviewcontroller, it works the same way. – Michael Aug 22 '11 at 03:39

Using delegate to pass data between views

3 Answers3