Passing data back :Delegate method not called

问题

I am working on an app that connects with google docs using oauth 2.0, once the user has connected, He clicks a button that goes to a tableView to show all the documents. For this I am using a segue and passing data forward. Now I want the user to select one document, put a checkmark on it and return to the viewcontroller passing data back and display wich document was selected. I read that for passing data back I needed to use a protocol and a delegate. I followed this: Passing Data between View Controllers but my problem is that my delegate method is not being called.

Here is my storyboard, just 2 views, a viewcontroller and a tablaviewvcontroller called VistaTableViewController.

When the user pushes the authenticate button, He connects with google docs using oauth. When he pushes the "Listar" button the VistaTableViewController appears.

Here is the code of VistaTableViewController.h where a define the protocol:

#import <UIKit/UIKit.h>
#import "GData.h"


@class VistaTableViewController;

@protocol VistaTableViewControllerDelegate <NSObject>
- (void)loqueselecciono:(VistaTableViewController *)controller didSelectDoc:(NSString *)documento;
@end


@interface VistaTableViewController : UITableViewController <UITableViewDataSource>
{
    IBOutlet UITableView *tablalistar;
    GDataFeedDocList *mDocListFeed2;
}

@property (nonatomic, weak) id <VistaTableViewControllerDelegate> delegate;
@property (nonatomic, strong) NSString *documento;
@property (nonatomic, retain) GDataFeedDocList *mDocListFeed2;

@end

Here is the code of VistaTableViewController.m where I call the delegate method:

#import "VistaTableViewController.h"


@implementation VistaTableViewController
{
    NSInteger selectedIndex;
}

@synthesize delegate;
@synthesize documento;
@synthesize mDocListFeed2;

- (void)viewDidLoad
{
    [super viewDidLoad];

    selectedIndex = [[mDocListFeed2 entries] indexOfObject:self.documento];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [[mDocListFeed2 entries] count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"tablalistar"];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"tablalistar"];
    }

    GDataEntrySpreadsheet *doc = [[mDocListFeed2 entries] objectAtIndex:indexPath.row];

    cell.textLabel.text = [[doc title] stringValue];

    if (indexPath.row == selectedIndex)
        cell.accessoryType = UITableViewCellAccessoryCheckmark;
    else
        cell.accessoryType = UITableViewCellAccessoryNone;

    return cell;
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{

    [tableView deselectRowAtIndexPath:indexPath animated:YES];
    if (selectedIndex != NSNotFound)
    {
        UITableViewCell *cell = [tableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:selectedIndex inSection:0]];
        cell.accessoryType = UITableViewCellAccessoryNone;
    }
    selectedIndex = indexPath.row;

    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];

    cell.accessoryType = UITableViewCellAccessoryCheckmark;

    GDataEntrySpreadsheet *doc = [[mDocListFeed2 entries] objectAtIndex:indexPath.row];

    NSString *theDoc = [[doc title] stringValue];

    [self.delegate loqueselecciono:self didSelectDoc:theDoc];
}

@end

Ok, so now I just need to tell ViewController to import VistaTableViewController and conform to its protocol.

here is the code of ViewController.h

#import <UIKit/UIKit.h>
#import "GTMOAuth2ViewControllerTouch.h"
#import "GData.h"
#import "VistaTableViewController.h"

@interface ViewController : UIViewController <VistaTableViewControllerDelegate>

- (GDataServiceGoogleDocs *)docsService;
- (void)authorize;
- (void) mifetch;
- (IBAction)autenticarse;
- (IBAction)listar:(id)sender;
- (void) ticket: (GDataServiceTicket *) ticket finishedWithFeed: (GDataFeedDocList *) feed error: (NSError *) error;

@property (nonatomic, retain) NSString *accessToken;
@property (nonatomic, retain) GDataFeedDocList *mDocListFeed;
@property (nonatomic, retain) GDataServiceTicket *mDoclistFetchTicket;


@end

Then in Viewcontroller.m I implement the delegate method as follows: (I just want to display an alert showing the title of de document that was selected).

- (void)loqueselecciono:(VistaTableViewController *)controller didSelectDoc:(NSString *)documento;
{
    [self.navigationController popViewControllerAnimated:YES];

    UIAlertView *alertView = [ [UIAlertView alloc] initWithTitle:@"doc seleccionado"
                                                         message:[NSString stringWithFormat:@"titulo: %@", documento]
                                                        delegate:self
                                               cancelButtonTitle:@"Dismiss"
                                               otherButtonTitles:nil];

    [alertView show];
}

and in Viewcontroller.m as well I wrote this to assign self to the delegate.

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    // Make sure your segue name in storyboard is the same as this line
    if ([[segue identifier] isEqualToString:@"displaydocs"])
    {
        VistaTableViewController *vistatableview = [[VistaTableViewController alloc] init];

        vistatableview.delegate = self;

        vistatableview = [segue.destinationViewController performSelector:@selector(setMDocListFeed2:) withObject:mDocListFeed];
    }
}

Ok, so I get de tableView displaying all the documents and the user can select one showing de checkmark but the delegate method is not being called so It does not return to the viewcontroller view and no data is passed back.

What am I missing?? Thanks!!

回答1:

When you write VistaTableViewController *vistatableview = [[VistaTableViewController alloc] init]; you are creating a new object. What you really want to do is use the segue.destinationViewController, which should be a VistaTableViewController and set its delegate to self.

As is, the object with the delegate is not the object being pushed and handling the view logic.

(Also, setMDocListFeed2 doesn't return an object so the assignment on performSelector is rather misleading.)

来源：https://stackoverflow.com/questions/11522428/passing-data-back-delegate-method-not-called