在其他类中关闭视图控制器后设置 UILabel 的文本

Question

我还没有找到可以回答我的问题的类似问题。

我的问题是：为什么我不能在 dissmissViewController 之后从另一个类访问 UILabel？

这是我的代码：

ClassA.h：

@interface ClassA : UIViewController {
    UILabel *_ErrorLabel;
    UIActivityIndicatorView *_acIn1;
}

@property (weak, nonatomic) IBOutlet UILabel *ErrorLabel;
@property (weak, nonatomic) IBOutlet UIActivityIndicatorView *acIn1;

ClassA.m：

shouldPerformSegue, prepareForSegue and statusBarStyle Methods

ClassB.h：

- (IBAction)dismiss;

ClassB.m：

- (IBAction)dismiss
{
  [self dismissViewControllerAnimated:YES completion:^{
      ClassA *login = [[ClassA alloc] init];
      [[login ErrorLabel] setText:@"Please use login."];
      [[login acIn1] stopAnimating];
      [[login acIn1] setHidesWhenStopped:YES];
      [[login acIn1] setHidden:YES];
  }];
}

这是我的代码，我真的希望有人能帮助我：我即将放弃我不知道为什么这行不通！

感谢您的帮助。

~马库斯

编辑1：

我有一个 ViewController ClassA，它包含两个文本字段，当您单击登录时，您会进入一个 TabBarController，其中一个选项卡包含 ClassB ViewController，并且在 ClassB ViewController 中有一个注销按钮 --> 关闭，当您单击此按钮时按钮你应该来到 ClassA ViewController 并且 ErrorLabel 文本应该改变。

完整类：A --> LoginViewControler.h

#import <UIKit/UIKit.h>
#import "ShowProfileViewController.h"

@interface LoginViewController : UIViewController <ShowProfileViewControllerDelegate> {
    UILabel *_ErrorLabel;
    UIActivityIndicatorView *_acIn1;
}

@property (weak, nonatomic) IBOutlet UITextField *usernameTextField;
@property (weak, nonatomic) IBOutlet UITextField *passwordTextField;
@property (weak, nonatomic) IBOutlet UILabel *ErrorLabel;
@property (weak, nonatomic) IBOutlet UIActivityIndicatorView *acIn1;

@end

完整类：A --> LoginViewController.m

#import "LoginViewController.h"
#import "NewsNavigationController.h"
#import "TabViewController.h"

@interface LoginViewController () <UITextFieldDelegate>

@end

@implementation LoginViewController

@synthesize usernameTextField;
@synthesize passwordTextField;
@synthesize ErrorLabel;
@synthesize acIn1;

- (void)viewDidLoad
{
    [super viewDidLoad];
    [usernameTextField setDelegate:self];
    [passwordTextField setDelegate:self];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}

- (UIStatusBarStyle)preferredStatusBarStyle
{
    return UIStatusBarStyleLightContent;
}

- (BOOL)shouldPerformSegueWithIdentifier:(NSString *)identifier sender:(id)sender
{
    
    if([identifier isEqualToString:@"login"])
    {
        [acIn1 startAnimating];
        [acIn1 setHidden:NO];
        if([self login]){
            return YES;
        } else {
            [self showErrorMessage:@"Data not correct!"];
            [acIn1 stopAnimating];
            [acIn1 setHidesWhenStopped:YES];
            [acIn1 setHidden:YES];
            return NO;
        }
    }
    else {
        [acIn1 stopAnimating];
        [acIn1 setHidesWhenStopped:YES];
        [acIn1 setHidden:YES];
        return NO;
    }
}

- (void)showErrorMessage:(NSString *)message
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error!"
                                                    message:message
                                                    delegate:self
                                                    cancelButtonTitle:@"OK"
                                                    otherButtonTitles:nil];
    [alert show];
}

- (BOOL)login
{
    NSString *usernameS = usernameTextField.text;
    NSString *passwordS = passwordTextField.text;
    
    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://localhost:8888/login.php?username=%@&password=%@", usernameS, passwordS]]];
    
    NSDictionary *jsonDictionary = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];

    NSDictionary *loginDic = [jsonDictionary objectForKey:@"login"];

    NSString *ErrorString = [loginDic objectForKey:@"returnString"];
    
    NSLog(@"[+] Login: %@", ErrorString);
    
    if ([ErrorString isEqualToString:@"Success"]){
        ErrorLabel.text = @"Login";
        return YES;
    }
    else {
        ErrorLabel.text = ErrorString;
        return NO;
    }
    
}

- (void)didDismissViewController
{
    [ErrorLabel setText:@"Bitte benutzen Sie den Login."];
    [acIn1 stopAnimating];
    [acIn1 setHidesWhenStopped:YES];
    [acIn1 setHidden:YES];
}

- (void)prepareForSegue:(UIStoryboardSegue *)inSegue sender:(id)inSender
{
    if([inSegue.identifier isEqualToString:@"login"])
    {
        ShowProfileViewController *vc = [[ShowProfileViewController alloc] init];
        vc.delegate = self;
        TabViewController *tabViewController = inSegue.destinationViewController;
        NewsNavigationController *theController = [[tabViewController viewControllers] objectAtIndex:0];
        [self presentViewController:vc animated:YES completion:nil];
    }
}


@end

完整类：B --> ShowProfileViewController.h

#import <UIKit/UIKit.h>

@protocol ShowProfileViewControllerDelegate

- (void)didDismissViewController;

@end

@interface ShowProfileViewController : UIViewController

@property (nonatomic, assign) id<ShowProfileViewControllerDelegate> delegate;

- (IBAction)dismiss;

@end

完整类：B --> ShowProfileViewController.m

#import "ShowProfileViewController.h"
#import "LoginViewController.h"

@interface ShowProfileViewController ()

@end

@implementation ShowProfileViewController


- (void)viewDidLoad
{
    [super viewDidLoad];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}

-(BOOL) textFieldShouldReturn:(UITextField *)textField{
    
    [textField resignFirstResponder];
    return YES;
}

- (void)viewWillAppear:(BOOL)inAnimated
{
    [super viewWillAppear:inAnimated];
}

- (IBAction)dismiss
{
    [self dismissViewControllerAnimated:YES completion:^{
        [self.delegate didDismissViewController];
    }];
}

@end

Answer 1

这不起作用，因为在完成块中，您正在创建 LoginViewController 的新实例，并设置其文本。您实际上应该做的是设置现有LoginViewController 的文本，它应该在关闭ShowProfileViewController 后出现

为了实现您想要的行为，您可以使用delegation pattern。如果你不熟悉这项技术，学习它是非常重要的。它在 iOS 和 Mac OS X 开发中被广泛使用。

您可能需要对以下代码进行一些调整。

在ShowProfileViewController.h 中，在@interface 之前添加：

@protocol ShowProfileViewControllerDelegate

- (void)didDismissViewController    

@end

另外，将以下属性声明添加到ShowProfileViewController：

@property (nonatomic, assign) id<ShowProfileViewControllerDelegate> delegate;

然后，更改 LoginViewController.h 的样子

#import "ShowProfileViewController.h" 

@interface LoginViewController : UIViewController <ShowProfileViewControllerDelegate> {
    UILabel *_ErrorLabel;
    UIActivityIndicatorView *_acIn1;
}

@property (weak, nonatomic) IBOutlet UILabel *ErrorLabel;
@property (weak, nonatomic) IBOutlet UIActivityIndicatorView *acIn1;

现在，在 ShowProfileViewController.m 中，替换 dismiss 方法中的代码，使其如下所示：

- (IBAction)dismiss
{
  [self dismissViewControllerAnimated:YES completion:^{
      [self.delegate didDismissViewController];
  }];
}

在LoginViewController.m中，添加如下方法：

- (void)didDismissViewController 
{
  [[self ErrorLabel] setText:@"Please use login."];
  [[self acIn1] stopAnimating];
  [[self acIn1] setHidesWhenStopped:YES];
  [[self acIn1] setHidden:YES];
}

最后，您需要将ShowProfileViewController 中的delegate 属性设置为指向LoginViewController 实例。在LoginViewController.m 中查找您创建的代码部分并呈现ShowProfileViewController 视图控制器并将delegate 属性设置为self。如果您使用故事板，您应该在 prepareForSegue: 中使用。

Answer 2

  ClassA *login = [[ClassA alloc] init];

正在创建一个全新的实例。不是你用来上 B 班的那个