为什么我的Objective-C代码会引发异常？

Question

I am new to Objective-C and i'm trying to program an iPhone App.

This is my code :

Head File:

#import <UIKit/UIKit.h>

@interface TutorialViewController : UIViewController{
    UILabel *labelText;
    UIImageView *imageView;
}
@property(nonatomic,retain) IBOutlet UILabel *labelText;
@property(nonatomic,retain) IBOutlet UIImageView *imageView;

-(IBAction) click:(id) sender;

@end

and this is the implementation:

#import "TutorialViewController.h"

@implementation TutorialViewController
@synthesize labelText;
@synthesize imageView;

-(void) click:(id)sender {
    imageView = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"1.png"]];
    NSString *titleOfButton = [sender titleForState:UIControlStateNormal];
    NSString *newText = [[NSString alloc]initWithFormat:@"%@",titleOfButton];
    // Change Image When Clicking Color Button
    if([titleOfButton isEqualToString:@"Blue"]){
        NSLog(@"Blue");
        UIImage *image = [UIImage imageNamed:@"1.png"];
        imageView.image = image;
        [image release];
    }else{
        UIImage *image = [UIImage imageNamed:@"2.png"];
        imageView.image = image;
        [image release];
        NSLog(@"Else");
    }
    labelText.text = newText;
    [newText release];
}
- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}
#pragma mark - View lifecycle
- (void)viewDidUnload
{
    [super viewDidUnload];
    self.labelText = nil;
}
-(void) dealloc{
    [labelText release];
    [imageView release];
    [super dealloc];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

@end

When i start the app, it throws an Exception:

'NSInternalInconsistencyException', reason: '-[UIViewController _loadViewFromNibNamed:bundle:] loaded the "TutorialViewController" nib but the view outlet was not set.'

Can any one help me with my code ?

And additionally , could you please tell me about those bad written behaviors in my code.

Many many thanks !

Answer 1

Connect the root UIView inside your Xib to the File's Owner's view.

Answer 2

Open up your .xib file, then in Objects click on View, then click on Connections Inspector and from there Control + Click on the circle in Referencing Outlets and drag it to the File's Owner and from the pop-up menu select view .... :)

EDIT:

Your View is the Main UIVIEW, whatever you will put in it or under it in hierarchy will be shown automatically. As you have used UIImageView in it (You can see the hierarchy of views and objects in Objects, column left to xib under the PlaceHolders). When you connect the UIView(parent View) to File's Owner. It shows all other views which are included in the main view. So when you connected the main view with File's Owner it resolved your issue.

Answer 3

Well, the error message seems pretty clear:

loaded the "TutorialViewController" nib but the view outlet was not set.'

Check the outlets on your TutorialViewController nib. Seems like the view outlet is not connected to anything. To fix it, connect your top-level-view to the outlet (control drag).