另一个UIViewController中的UIViewController的新实例：为什么我不能设置实例变量？

Question

所以我有一个叫做MyTabBarViewController的UIViewController子类，它有一个UIScrollView。 MyTabBarViewController的内部我创建了另一个名为PhotoViewController的UIViewController子类的实例。 （注：我这样做，所以我可以使用IB设置IBOutlets）

我想从我的TabBarViewController设置每个PhotoViewController实例的标签。并且我为每个PhotoViewController初始化了一个nib，所以我的印象是每个PhotoViewController实例都会连接到它们各自的IBOutlets - 这使我可以简单地使用pvc.label.text = @“我想要的文本”来设置标签名称。

你能解释为什么我的逻辑不正确吗？因为它不工作，不确定该怎么做。 ： -/

MyTabBarViewController.m

#import "MyTabBarViewController.h" 


@implementation MyTabBarViewController 
@synthesize pageControl,scroller; 

-(IBAction)clickPageControl:(id)sender 
{ 
    int page=pageControl.currentPage; 
    CGRect frame=scroller.frame; 
    frame.origin.x = frame.size.width * page; 
    frame.origin.y = 0; 
    [scroller scrollRectToVisible:frame animated:YES]; 
} 

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView 
{ 
    int page = scrollView.contentOffset.x/scrollView.frame.size.width; 
    pageControl.currentPage=page; 
} 

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

- (void)dealloc 
{ 
    [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]; 
    scroller.delegate=self; 
    scroller.pagingEnabled=YES; 
    scroller.directionalLockEnabled=YES; 
    scroller.showsHorizontalScrollIndicator=NO; 
    scroller.showsVerticalScrollIndicator=NO; 
    scroller.contentSize=CGSizeMake(pageControl.numberOfPages*scroller.frame.size.width, scroller.frame.size.height); 
    CGFloat scrollWidth = 0; 
    int pageNumber = 0; 
    for (int i=0; i<3; i++) 
    { 
     PhotoViewController *pvc = [[PhotoViewController alloc] initWithNibName:@"PhotoViewController" bundle:nil]; 
     CGRect rect = scroller.frame; 
     rect.size.height = scroller.frame.size.height; 
     rect.size.width = scroller.frame.size.width; 
     rect.origin.x = scroller.frame.origin.x + scrollWidth; 
     rect.origin.y = scroller.frame.origin.y; 
     pvc.label.text = [NSString stringWithFormat:@"%d", pageNumber]; 
     pvc.label.textColor = [UIColor redColor]; 
     pvc.view.frame = rect; 
     [scroller addSubview:pvc.view]; 
     [pvc release]; 
     pageNumber++; 
     scrollWidth += scroller.frame.size.width; 
    } 
    pageControl.numberOfPages=3; 
    pageControl.currentPage=0; 
    [self.view addSubview:scroller]; 
} 

- (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 

PhotoViewController.h是相当直接的。而PhotoViewController.m也是，但我已经包含了执行文件，如果我的问题在那里。

PhotoViewController.m

#import "PhotoViewController.h" 


@implementation PhotoViewController 
@synthesize label, imageView, sendButton, cancelButton; 

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

- (void)dealloc 
{ 
    [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. 
} 

- (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 

Answer 1

你不能设置这样的任何视图相关的值（使对象和设置从该视图其他输入）。

因为您不能在任何视图控制器的viewDidLoad之前设置任何级别的值。您需要什么，您需要相应地为标签设置字符串类型的属性，然后在MyTabBarViewController中设置它们的值，然后从堆栈中拾取对象在PhotoViewController中使用MyTabBarViewController类，然后访问它的属性并设置标签。

对于从堆栈采摘视图对象，你需要使用此行

MyTabBarViewController *obj = (MyTabBarViewController *)[self.navigationController.viewControllers objectAtIndex: [self.navigationController.viewControllers count]-2]; 

Answer 2

的IBOutlet中实体不存在，直到viewDidLoad中，而且一般不发生，直到你开始表演。因此，在MyTabBarViewController中，您正在寻找一个不存在的标签等。 （当然，Objective-C方便地忽略了nil指针的调用，所以它看起来像是一切正常 - 没有任何反应。）

根据规范，您可以通过引用视图的视图属性来触发加载控制器，但我从来没有尝试过。