UIPickerView ios problems - unrecognized selector

I think this is probably a very rudimentary question, but after a few hours of searching, I can find some people with my issue, but none of the solutions I found work.

I am just getting my feet wet with iPhone development, though I have writing Android and Blackberry apps, so the Objective-C is a bit of a switch from Java.

First of all, when I try to open the screen with a UIPickerView on it, I get this error message:

[UIViewController numberOfComponentsInPickerView:]: unrecognized selector sent to instance 0x4b4e0d0 2011-09-09 15:57:19.619 TabBar[4945:207] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIViewController numberOfComponentsInPickerView:]: unrecognized selector sent to instance 0x4b4e0d0'

Here is my header file:

#import <UIKit/UIKit.h>

@interface ThirdViewController : UIViewController <UIPickerViewDelegate,        UIPickerViewDataSource>{
UILabel *setUnits;
UIPickerView *pickerView;
NSMutableArray *pickItems;
}
@property (retain, nonatomic) UIPickerView *pickerView;
@property (retain, nonatomic) NSMutableArray *pickItems;

@end

And here is my implementation file:

#import "ThirdViewController.h"

@implementation ThirdViewController

@synthesize pickerView;
@synthesize pickItems;

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

- (void)didReceiveMemoryWarning
{
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

/*
// Implement loadView to create a view hierarchy programmatically, without using a nib.
- (void)loadView
{
}
*/

// Implement vi开发者_开发技巧ewDidLoad to do additional setup after loading the view, typically from a     nib.
- (void)viewDidLoad {
    [super viewDidLoad];

    pickItems = [[NSMutableArray alloc] init];
    [pickItems addObject:@"Pounds"];
    [pickItems addObject:@"Kilograms"];
}

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {

    return 1; //give components here
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:    (NSInteger)component {

     return [pickItems count];   //give rows here
}

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component {   
    return [pickItems objectAtIndex:row];  // give titles 
}

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component {
    //Do the step here
}

- (void)dealloc {
     [super dealloc];
}
@end

I have checked, and both the delegate and dataSource are connected to the file's Owner. Am I missing something?

Thanks.

I suspect that in the Interface Builder / xib file you need to change your UIViewController class to the ThirdViewController class. In any case the error message is telling you that your are sending the message to a UIViewController instance and not an instance of the subclass you have created. Common (but not the only) cause is IB / xib settings - but you make the error programmatically too. (With IB / xib it is easy to do, even if you've been using iOS for a while.)

Where you are initializing your pickerView? if you are doing with xib then it should be connected, i could find pickerView as IBOutlet in your code.

When you call numberOfComponentsInPickerView:, it appears that you are calling it on an instance of UIViewController and not an instance of ThirdViewController. If necessary, cast the viewController to make sure the compiler knows it is an instance of the latter.