模态视图的 iPad 问题：创建视图控制器后模态视图标签为空

Posted 2023-03-11

【中文标题】模态视图的 iPad 问题：创建视图控制器后模态视图标签为空

【英文标题】：iPad issue with a modal view: modal view label null after view controller is created

【发布时间】：2010-06-01 03:34:53

【问题描述】：

这是一个奇怪的问题。我为我的模态视图创建了一个带有 nib 文件的视图控制器。在那个视图上有一个标签、数字和文本视图。当我从源视图创建视图时，我尝试设置标签，但它显示标签是null (0x0)。有点奇怪......有什么建议吗？现在让我们看一下代码（我把所有的代码都放在这里，因为这比我能解释的要多）：

模态视图控制器 - 在 IB 中，标签连接到 UILabel 对象：

    @implementation ModalViewController

@synthesize delegate;
@synthesize goalLabel, goalText, goalNumber;

// Done button clicked
- (void)dismissView:(id)sender 

    // Call the delegate to dismiss the modal view
    if ([delegate respondsToSelector:@selector(didDismissModalView: newText:)]) 

        NSNumber *tmpNum = goalNumber;
        NSString *tmpString = [[NSString alloc] initWithString:[goalText text]];
        [delegate didDismissModalView:tmpNum newText:tmpString];

        [tmpNum release];
        [tmpString release];
    


- (void)cancelView:(id)sender 

    // Call the delegate to dismiss the modal view
    if ([delegate respondsToSelector:@selector(didCancelModalView)])
        [delegate didCancelModalView];


-(void) setLabelText:(NSString *)text 
    [goalLabel setText:text];


/*
 // The designated initializer.  Override if you create the controller programmatically and want to perform customization that is not appropriate for viewDidLoad.
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil 
    if ((self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil])) 
        // Custom initialization
    
    return self;

*/

-(void) viewWillAppear:(BOOL)animated 

    [super viewWillAppear:animated];

    // bring up the keyboard....
    [goalText becomeFirstResponder];



// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad 
    [super viewDidLoad];

    // set the current goal number to -1 so we know none was set
    goalNumber = [NSNumber numberWithInt: -1];

    // Override the right button to show a Done button
    // which is used to dismiss the modal view
    self.navigationItem.rightBarButtonItem = [[[UIBarButtonItem alloc]
                                               initWithBarButtonSystemItem:UIBarButtonSystemItemDone
                                               target:self
                                               action:@selector(dismissView:)] autorelease];

    // and now for the cancel button
    self.navigationItem.leftBarButtonItem = [[[UIBarButtonItem alloc]
                                               initWithBarButtonSystemItem:UIBarButtonSystemItemCancel
                                               target:self
                                              action:@selector(cancelView:)] autorelease];

    self.navigationItem.title = @"Add/Update Goals";




- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation 
    // Overriden to allow any orientation.
    return YES;



- (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.



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



- (void)dealloc 
    [super dealloc];



@end

这里是创建视图控制器、设置变量和显示的地方：

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

    // put a checkmark....
    UITableViewCell *tmpCell = [tableView cellForRowAtIndexPath:indexPath];
    [tmpCell setAccessoryType:UITableViewCellAccessoryCheckmark];

    // this is where the popup is gonna popup!
    // ===> HEre We Go!

    // Create the modal view controller
    ModalViewController *mdvc = [[ModalViewController alloc] initWithNibName:@"ModalDetailView" bundle:nil];

    // We are the delegate responsible for dismissing the modal view 
    [mdvc setDelegate:self];

    // Create a Navigation controller
    UINavigationController *navController = [[UINavigationController alloc]
                                             initWithRootViewController:mdvc];

    // set the modal view type
    navController.modalPresentationStyle = UIModalPresentationFormSheet;

    // set the label for all of the goals....
    if (indexPath.section == 0 && indexPath.row == 0) 
        [mdvc setLabelText:[[[NSString alloc] initWithString:@"Long Term Goal 1:"] autorelease]];
        [mdvc setGoalNumber:[NSNumber numberWithInt:1]];
    

    if (indexPath.section == 0 && indexPath.row == 1) 
        [mdvc setLabelText:[[[NSString alloc] initWithString:@"Long Term Goal 2:"] autorelease]];
        [mdvc setGoalNumber:[NSNumber numberWithInt:2]];
    

    if (indexPath.section == 0 && indexPath.row == 2) 
        [mdvc setLabelText:[[[NSString alloc] initWithString:@"Long Term Goal 3:"] autorelease]];
        [mdvc setGoalNumber:[NSNumber numberWithInt:3]];
    

    if (indexPath.section == 0 && indexPath.row == 3) 
        [mdvc setLabelText:[[[NSString alloc] initWithString:@"Long Term Goal 4:"] autorelease]];
        [mdvc setGoalNumber:[NSNumber numberWithInt:4]];
    


    if (indexPath.section == 1 && indexPath.row == 0) 
        [mdvc setLabelText:[[[NSString alloc] initWithString:@"Short Term Goal 1:"] autorelease]];
        [mdvc setGoalNumber:[NSNumber numberWithInt:5]];
    

    if (indexPath.section == 1 && indexPath.row == 1) 
        [mdvc setLabelText:[[[NSString alloc] initWithString:@"Short Term Goal 2:"] autorelease]];
        [mdvc setGoalNumber:[NSNumber numberWithInt:6]];
    

    if (indexPath.section == 1 && indexPath.row == 2) 
        [mdvc setLabelText:[[[NSString alloc] initWithString:@"Short Term Goal 3:"] autorelease]];
        [mdvc setGoalNumber:[NSNumber numberWithInt:7]];
    

    if (indexPath.section == 1 && indexPath.row == 3) 
        [mdvc setLabelText:[[[NSString alloc] initWithString:@"Short Term Goal 4:"] autorelease]];
        [mdvc setGoalNumber:[NSNumber numberWithInt:8]];
    

    // show the navigation controller modally
    [self presentModalViewController:navController animated:YES];

    // Clean up resources
    [navController release];
    [mdvc release];

    // ==> Ah... we are done...

【参考方案1】：

答案是盯着我的脸！

这是我所做的：

为委托添加了一个新功能

@protocol ModalViewControllerDelegate <NSObject>
@required
    - (void)didDismissModalView:(NSNumber *)goalNbr newText:(NSString *)textToSave;
    - (void)didCancelModalView;
    - (void)willShow:(id)theView;
@end

在viewWillAppear 函数中，我添加了以下内容：

if ([delegate respondsToSelector:@selector(willShow:)])
    [delegate willShow:self];

这允许完全访问将要显示的模态视图，因此我们能够更改活动模态视图中的标签、文本框和变量。

- (void)willShow:(ModalViewController *)theView 

    [theView.goalLabel setText:labelText];
    [theView setGoalNumber:goalNumber];
    [theView.goalText setText:goalText];

【参考方案2】：

为了完整起见，万一其他人偶然发现了这个（它帮助了我）......

模态视图控制器的接口需要定义一个变量来保存委托：

@protocol ReminderPhotoViewDelegate <NSObject>
@required
- (void)willShow:(id)theView;
@end
@interface ReminderPhotoViewController : UIViewController 
    id<ReminderPhotoViewDelegate> delegate;
    UIImageView *reminderImage;
    UILabel *reminderLabel;

@property (assign) id<ReminderPhotoViewDelegate> delegate;
@property (nonatomic, retain) IBOutlet UIImageView *reminderImage;
@property (nonatomic, retain) IBOutlet UILabel *reminderLabel;
@end

在模态控制器的实现中，一定要综合这些属性：

@implementation ReminderPhotoViewController
@synthesize reminderImage, reminderLabel;
@synthesize delegate;

无论你的“调用”控制器是什么，都必须在它自己的实现中声明对这个协议的支持：

#import "ReminderPhotoViewController.h"
@interface ReminderViewController : UIViewController <ReminderPhotoViewDelegate> 

最后，当您创建模态控制器的实例时，您需要将调用类设置为其委托：

ReminderPhotoViewController *photo = [[ReminderPhotoViewController alloc] init];
[photo setDelegate:self];

这是一组更完整的声明和代码 - 这正是答案显示的内容，只是有更多的支持代码。

然后，如上所述，您的调用控制器从协议中添加方法：

- (void)willShow:(ReminderPhotoViewController *)theView 
    theView.reminderImage.image = selectedImage;
    theView.reminderLabel.text = selectedText;