What does the "unrecognized selector sent to instance" error mean?

I am parsing XML, and getting this erro开发者_Python百科r:

[NSCFString event_Title]: unrecognized selector sent to instance 0x6b0c130 2010-12-22 19:48:38.719 TestDemo[2234:207] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString event_Title]: unrecognized selector sent to instance 0x6b0c130' * Call stack at first throw:

Here is my code:

#import "RootViewController.h"
#import "TestDemoAppDelegate.h"
#import "Events.h"
#import "DetailedViewController.h"
@implementation RootViewController

#pragma mark -
#pragma mark View lifecycle


- (void)viewDidLoad {
    [super viewDidLoad];
    self.title=@"Cities Name";
    appDelegate=(TestDemoAppDelegate *)[[UIApplication sharedApplication]delegate];

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;
}


/*
- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
}
*/
/*
- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
}
*/
/*
- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
}
*/
/*
- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
}
*/

/*
 // Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    // Return YES for supported orientations.
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
 */


#pragma mark -
#pragma mark Table view data source

// Customize the number of sections in the table view.
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}


// Customize the number of rows in the table view.
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [appDelegate.listArray count];
}

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease];
    }

    Events *event=[[Events alloc] init];
    event=[appDelegate.listArray objectAtIndex:indexPath.row];
    NSLog(@"event abajdfkjioteh@",event.event_Title);
//    cell.textLabel.text=event.event_Title;

    return cell;

}


/*
// Override to support conditional editing of the table view.
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath {
    // Return NO if you do not want the specified item to be editable.
    return YES;
}
*/


/*
// Override to support editing the table view.
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {

    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete the row from the data source.
        [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
    }   
    else if (editingStyle == UITableViewCellEditingStyleInsert) {
        // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view.
    }   
}
*/


/*
// Override to support rearranging the table view.
- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath {
}
*/


/*
// Override to support conditional rearranging of the table view.
- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath {
    // Return NO if you do not want the item to be re-orderable.
    return YES;
}
*/


#pragma mark -
#pragma mark Table view delegate

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

    if (indexPath.row) {


     DetailedViewController *detailViewController = [[DetailedViewController alloc] initWithNibName:@"DetailedViewController" bundle:nil];
     // ...
     // Pass the selected object to the new view controller.
     [self.navigationController pushViewController:detailViewController animated:YES];
     [detailViewController release];
    }
}


#pragma mark -
#pragma mark Memory management

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

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

- (void)viewDidUnload {
    // Relinquish ownership of anything that can be recreated in viewDidLoad or on demand.
    // For example: self.myOutlet = nil;
}


- (void)dealloc {

    [super dealloc];
}

I am trying cell.textLabel.text=[appDelegate.listArray objectAtIndex:IndexPath.row];. All the data in my array is displayed in my tableview.

When I am trying with Class Reference, with that I can display only Event_title only on my tableview. It's crashing my application.

Event *aEvent=[appDelegate.listArray objectAtIndex:IndexPath.row];
cell.textLabel.text=aEvent.Event_title;

If I call this my application get crash.

It looks like you accidentally set event to a NSString on this line

Events *event=[[Events alloc] init];
event=[appDelegate.listArray objectAtIndex:indexPath.row];

Try this

Events *event=[[Events alloc] init];
event.event_Title=[appDelegate.listArray objectAtIndex:indexPath.row];