在两个ViewControllers之间传递数据问题

Question

嗨，我有两个viewControllers。

NewsViewController

#import "SingleViewController.h" 
@interface NewsViewController : UIViewController { 
} 
- (NSString *)getFirstImage:(NSString *)htmlString; 
@end 

和实现文件：

#import "SingleViewController.h" 
SingleViewController *singleViewController; 

@interface NewsPadViewController() <UIActionSheetDelegate> 

- (void)loadSubscriptions; 

@property (nonatomic, assign) BOOL wrap; 
@property (nonatomic, retain) NSMutableArray *items; 

@end 

@implementation NewsPadViewController 
....CODE.... 
- (void)carouselCurrentItemTapped{ 
    //[self addSubview:articolo]; 
    MWFeedItem *item =[reader.feedItems objectAtIndex:[carousel currentItemIndex]]; 

    NSLog(@"Current Item tappped, index: %d", [carousel currentItemIndex]); 

    singleViewController.prova.text=@"CIAO"; 
    singleViewController.ciao=@"sample"; 
    [singleViewController.web loadHTMLString:item.summary baseURL:nil]; 
    NSLog(@"conternutio:"); 
    NSLog(singleViewController.ciao); 
} 

SingleViewController.h

#import <UIKit/UIKit.h> 

@interface SingleViewController : UIViewController{ 
    @public 
    UIWebView *web; 
    UILabel *prova; 
    NSString *ciao; 
} 
@property (nonatomic,retain) IBOutlet UIWebView *web; 
@property (nonatomic,retain) IBOutlet UILabel *prova; 
@property (nonatomic,retain) IBOutlet NSString *ciao; 
@end 

和SingleViewController.m

#import "SingleViewController.h" 

@implementation SingleViewController 
@synthesize web,prova,ciao; 

- (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 

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

- (void)viewDidUnload 
{ 
    [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); 
} 

@end 

为什么我无法从SingleViewController中的对象访问NewsPadViewController？我的错误在哪里？感谢 UPADATE

- (void)carouselCurrentItemTapped{ 
    //[self addSubview:articolo]; 
    MWFeedItem *item =[reader.feedItems objectAtIndex:[carousel currentItemIndex]]; 

    NSLog(@"Current Item tappped, index: %d", [carousel currentItemIndex]); 

SingleViewController *singleViewController = [[SingleViewController alloc] initWithNibName:@"SingleViewController" bundle:[NSBundle mainBundle]];  

    singleViewController.prova.text=@"CIAO"; 
    singleViewController.ciao=@"sample"; 
    [singleViewController.web loadHTMLString:item.summary baseURL:nil]; 
    NSLog(@"conternutio:"); 
    NSLog(singleViewController.ciao); 
    [singleViewController setOpz:@"sample"]; 

} 

Answer 1

我没有看到SingleViewController的任何实例。你有一个指向它的指针，但是我没有看到你实际创建它的代码示例中的任何地方。

某处你需要的东西，如：

if (!singleViewController) { 
    singleViewController = [[SingleViewController alloc] init]; 
} 

或

SingleViewController *singleViewController = [[SingleViewController alloc] initWithNibName:@"SingleView" bundle:nil]; 

或从别的地方你需要发送的NewsViewController指向SingleViewController的现有实例的消息或设置实例变量。