UILabel not updating

Question

Sorry the basic question, but this bugs me for a while now.

I create a details view from a UITable and try to dynamically set its labels, but they are not updating:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
  myObject *tmpObj = [[myObject objectAtIndex:indexPath.section] objectAtIndex:indexPath.row];

  myViewController *tmpVC = [[myViewController alloc] initWithNibName:@"NIBfile" bundle:nil];

  [tmpVC.myLabel setText:tmpObj.myTitle];   // The debugger shows the text: myTitle = "myText"
  NSLog(@"%@", tmpVC.myLabel);              // NSLog SHOWS NULL

  [self.navigationController pushViewController:tmpVC animated:YES];
  [tmpObj release];
}

the connections in Interface Builder are set. The Connections Tab for File Owner shows

'myLabel' - 'Label (myLabel)'

any ideas why the value is not coming through?

A few more Observations:

• I also have an IBAction connected. This method is properly called when I click the connected button.
• I got a few pointers to my NSLog-statement, whether that should not better use tmpVC.myLabel.text, but trying also returns NULL.
• myLabel is declared as IBOutlet UILabel *myLabel in the interface. The property is defined as nonatomic, retain.

THERE'S THE LIGHT:

After playing around with it for a bit more I moved the pushViewController statement above the label updates. That resolved the label updates.

Working code looks like this:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
 myObject *tmpObj = [[myObject objectAtIndex:indexPath.section] objectAtIndex:indexPath.row];

 myViewController *tmpVC = [[myViewController alloc] initWithNibName:@"NIBfile" bundle:nil];

 [self.navigationController pushViewController:tmpVC animated:YES];

 [tmpVC.myLabel setText:tmpObj.myTitle];   // The debugger shows the text: myTitle = "myText"
 NSLog(@"%@", tmpVC.myLabel);              // NSLog SHOWS NULL

 [tmpObj release];
}

But I don't understand why I need to push my viewController first ???

Answer 1

If tmpVC.myLabel is NULL, that probably indicates that you have not made the necessary connection in Interface Builder from the UILabel to your myLabel instance variable.

Answer 2

Is it not because your NSLog is trying to print out the actual label object. Should you not have

NSLog(@"%@", tmpVC.myLabel.text);

In Response to the added information: Your other issue would appear to be that you have linked an NSString to your label. You have to link it to a UILabel. So where you declare your myLabel var, change it to UILabel *myLabel, and the same for any matching property.

Answer 3

It may be due to wrong Data Type assign to tmpVC.myLabel.text in NSLog() statement. Try this NSLog(@"%s", tmpVC.myLabel.text); it may worked.

Answer 4

Did you @synthesize your myLabel property in myViewController.m? You should be able to do something like:

tmpVC.myLabel.text = tmpObj.myTitle;

Answer 5

Not sure but I think this is what's going on:

When the view is pushed, the controller loads the view from the nib and hooks up the actions and outlets. Before this, the outlets are not connected, so tmpVC.myLabel is nil.

If you want to be sure, you could put a breakpoint in viewDidLoad of tmpVC to see when the view is loaded.

Answer 6

That's because the controller's view is lazily created only when accessed. Pushing the controller accesses the view.

Alternatively, if you add a line to access the view property, it will work too:

  myViewController *tmpVC = [[myViewController alloc] initWithNibName:@"NIBfile" bundle:nil];
  tmpVC.view;   // Force view creation
  [tmpVC.myLabel setText:tmpObj.myTitle];   // The debugger shows the text: myTitle = "myText"
  NSLog(@"%@", tmpVC.myLabel);              // NSLog will display "myText"
  [self.navigationController pushViewController:tmpVC animated:YES];