使用 UIButton 转换 UIView 时出现问题

Question

我是一个非常缺乏经验的开发人员，遇到了一个应该很容易的问题，但是在阅读了几个小时的苹果开发人员指南和该网站上的许多不同问题后，我仍然感到困惑。

我想做的就是通过 UIButton 从根视图控制器转换到下一个视图控制器。

这是 appdelegate.h：

#import <UIKit/UIKit.h>

@class MainViewController;

@interface MDAppDelegate : NSObject <UIApplicationDelegate> {

    UIWindow *window;
    UINavigationController *navigationController;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet UINavigationController *navigationController;

@end

来自 Appdelegate.m 的重要内容：

#import "MDAppDelegate.h"
#import "MainViewController.h"

@implementation MDAppDelegate


@synthesize window, navigationController;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions  (NSDictionary *)launchOptions

{

    // Override point for customization after application launch.
    [window addSubview:navigationController.view];
    [self.window makeKeyAndVisible];
    return YES;
}

MainViewController.h：

#import <UIKit/UIKit.h>


@interface MainViewController : UIViewController {

UIButton *cityButton;

}

@property (nonatomic, retain) IBOutlet UIButton *cityButton;

- (IBAction)chooseCityAction:(id)sender;

@end

最后，MainViewController.m：

#import "MainViewController.h"
#import "DailyDealViewController.h"


@implementation MainViewController
@synthesize cityButton;

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

    }

return self;

}

- (void)dealloc
{
    [cityButton release];

    [super dealloc];
}

- (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

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

    UIBarButtonItem *temporaryBarButtonItem = [[UIBarButtonItem alloc] init];
    temporaryBarButtonItem.title = @"Back";
self.navigationItem.backBarButtonItem = temporaryBarButtonItem;
[temporaryBarButtonItem release];


}

- (void)viewDidUnload
{
    [self setCityButton:nil];
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

- (IBAction)chooseCityAction:(id)sender {

    DailyDealViewController *dailyDealViewController = [[DailyDealViewController alloc]initWithNibName:@"DailyDealViewController" bundle:nil];

    [dailyDealViewController release];

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

}
@end

这是错误：

2011-10-03 21:56:14.258 MD[4235:207] *** Terminating app due to uncaught exception
'NSUnknownKeyException', reason: '[<UIViewController 0x4b434c0>
setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key 
cityButton.'

我很想知道我错过了什么。

Answer 1

您在推送之前已经发布了 dailyDealViewController。将release语句移至pushViewController语句之后。