无法使用带有 presentModalViewController 的协议和委托在视图之间发送数据

Question

我正在做电梯的事情。我在使用 presentModalViewController 发送具有不同视图的数据时遇到问题。我收到红色消息“favoriteColorString”属性未找到。我复制了完全相同但不同的表单名称和按钮。 “favoriteColorString”出现错误，无法发送电梯2数据。

我尝试了两种不同的方法。

  Elevator2View.favoriteColorString = [[NSString alloc] initWithFormat:@"Your favorite color is %@", favoriteColorTextField.text];

和

  favoriteColorString = [[NSString alloc] initWithFormat:@"Your favorite color is %@", favoriteColorTextField.text];

这是我的代码：

ElevatorView.h

#import <UIKit/UIKit.h>
#import "Elevator2View.h"

@interface ElevatorView : UIViewController<PassSecondColor>
 {

Elevator2View   *Elevator2View;

IBOutlet UITextField     *favoriteColorTextField;
IBOutlet UILabel         *favoriteColorLabel;
IBOutlet UILabel         *secondFavoriteColorLabel;

NSString        *secondFavoriteColorString;

}

@property (nonatomic, retain) Elevator2View *Elevator2View;
@property (nonatomic, retain) IBOutlet UITextField  *favoriteColorTextField;
@property (nonatomic, retain) IBOutlet UILabel      *favoriteColorLabel;
@property (nonatomic, retain) IBOutlet UILabel      *secondFavoriteColorLabel;

@property (copy) NSString   *secondFavoriteColorString;

@end

ElevatorView.m

#import "ElevatorView.h"
#import "Elevator2View.h"
    @implementation ElevatorView
@synthesize Elevator2View, favoriteColorTextField, favoriteColorLabel, secondFavoriteColorLabel;
@synthesize secondFavoriteColorString;



-(IBAction)level1:(id)sender;{
   favoriteColorTextField.text = @"1";
      Elevator2View.favoriteColorString = [[NSString alloc] initWithFormat:@"Your favorite color is %@", favoriteColorTextField.text];

      [self presentModalViewController:[[[Elevator2View alloc] init]
                                  autorelease] animated:NO];
}

Elevator2View.h

#import <UIKit/UIKit.h>

@protocol PassSecondColor <NSObject>
@required
- (void) setSecondFavoriteColor:(NSString *)secondFavoriteColor;
@end

@interface Elevator2View : UIViewController{
IBOutlet UITextField *secondFavoriteColorTextField;
IBOutlet UILabel     *favoriteColorLabel;
IBOutlet UILabel     *secondFavoriteColorLabel;
NSString             *favoriteColorString;
id <PassSecondColor> delegate;

}

@property (copy) NSString   *favoriteColorString;



@property (nonatomic, retain) IBOutlet UITextField  *secondFavoriteColorTextField;
@property (nonatomic, retain) IBOutlet UILabel      *favoriteColorLabel;
@property (nonatomic, retain) IBOutlet UILabel      *secondFavoriteColorLabel;
@property (retain) id delegate;

@end

Elevator2View.m

#import "Elevator2View.h"

@interface Elevator2View ()

@end

@implementation Elevator2View
@synthesize secondFavoriteColorTextField, favoriteColorLabel, secondFavoriteColorLabel;
@synthesize favoriteColorString;
@synthesize delegate;

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

- (void) viewWillAppear:(BOOL)animated
{
    favoriteColorLabel.text = favoriteColorString;  
}

- (void) viewWillDisappear:(BOOL) animated
{
//  [[self delegate] setSecondFavoriteColor:secondFavoriteColorTextField.text];
}


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

- (void)didReceiveMemoryWarning
{
   [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}



@end

见http://www.theappcodeblog.com/?p=90

Answer 1

“找不到属性”的原因是您将 ivar 命名为与类相同。 点符号只是一种语法糖：object.property = value 等价于 [object setProperty:value]。在Objective C 中，类也是对象，当您调用Elevator2View.favoriteColorString = whatever 时，Xcode 显然认为您正在尝试调用类Elevator2View 的class 方法setFavoriteColorString。

摆脱这个错误很容易：只需将您的 ivar Elevator2View *Elevator2View 重命名为其他名称。事实上，Xcode 4.4 和更新的版本会为你的属性自动合成 ivar：如果你有一个属性 propertyName，那么 Xcode 会自动合成 ivar _propertyName。您的财产Elevator2View 将拥有_Elevator2View ivar。因此，除非您真的需要具有不同命名方案的 ivars，否则您可以摆脱 @synthesize，并且您也不需要为您的属性声明 ivars。

（虽然我更喜欢为属性声明 ivars（遵循 Xcode 命名方案），因为 lldb 通常不会在对象检查器中显示自动合成的不声明 ivars。）

那是关于属性、变量和命名约定的。但是你在这段代码中做了什么？

-(IBAction)level1:(id)sender;{
   favoriteColorTextField.text = @"1";
      Elevator2View.favoriteColorString = [[NSString alloc] initWithFormat:@"Your favorite color is %@", favoriteColorTextField.text];

      [self presentModalViewController:[[[Elevator2View alloc] init]
                                  autorelease] animated:NO];
}

你设置Elevator2View的值 - 你的实例变量的 - 属性，然后创建Elevator2View的全新对象class并呈现 作为模态视图控制器。 （顺便说一句，presentModalViewController:animated: 在 iOS 6.0 中已弃用）。当然，这个全新的新 Elevator2View 对象不知道Elevator2View（你的实例变量的）属性是什么！