Question

pass data from FirstViewController to DetailViewController. i can not set the text of label in DetailViewController; FirstViewController is a tableview and it is good.

i use method updateRowNumber to set the rowNumber . and in DetailViewController, i can use debugger to see the rowNumber is correct. but the label’s text is not showed on the view.

anyone can help me out?

in my FirstViewController

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

if (dvController == nil)
{
    DetailViewController *aController = [[DetailViewController alloc] initWithNibName:@"DetailViewController" bundle:nil];

    self.dvController = aController;

    [aController release];
}   

[[self navigationController] pushViewController:dvController animated:YES];
[dvController updateRowNumber:indexPath.row];


}

in my DetailViewController.h

#import <UIKit/UIKit.h>

@interface DetailViewController : UIViewController
{
    int rowNumber;
    IBOutlet UILabel *message;
}

@property(readwrite) int rowNumber;
@property(nonatomic, retain) IBOutlet UILabel *message;
- (void) updateRowNumber:(int) theindex;


@end

in my DetailViewController.m

#import "DetailViewController.h"


@interface DetailViewController ()

@end

@implementation DetailViewController

@synthesize message, rowNumber;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
    // Custom initialization
}
return self;
}

- (void) updateRowNumber: (int) theindex
{
    rowNumber = theindex + 1;
    message.text = [NSString stringWithFormat:@"row %i was clicked", rowNumber];
}

- (void)dealloc
{
    [message release];
    [super dealloc];
}

- (void)viewDidLoad
{
    message.text = [NSString stringWithFormat:@"row %i was clicked ", rowNumber];
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Do any additional setup after loading the view from its nib.
}

- (void)viewWillAppear:(BOOL)animated
{
    //message.text = [NSString stringWithFormat:@"row %i was clicked ", rowNumber];

    [super viewWillAppear: animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear: animated];
}


- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

Answer 1

You’ll need to learn how the view is loaded, the process is well described in the documentation

What happens is that the view and all the outlets are nil until the view is loaded, you can make sure it is loaded by calling self.view; before configuring the outlet at updateRowNumber:

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Please also note, you are better to call [super viewDidLoad] in the beginning of the overridden viewDidLoad, it makes sense as you need to let UIViewContorller to do it’s staff before you do some customized logic, the dealloc is different as you need to do your logic before the standard NSObject -dealloc fires. Hope it’s understandable.