Question

我需要在我的应用程序的两个类（从ViewController Class_A到ViewController Class_B）之间传递NSString，我已经在StackOverflow上搜索了，但这是我的情况的简化代码：

Class_A.h

#import "Class_B.h"

@interface ViewController : UIViewController {
    NSString *stringToPass;
}

@property (retain, nonatomic) NSString *stringToPass;
-(NSString *)stringPassage:(id)sender;

@end

Class_A.m

- (NSString *)stringPassage:(id)sender{
    NSString *string = @"A FANTASTIC STRING!"; //here I define string INTO the - (NSString *) method
    NSLog(@"String to pass: %@",string);
    return string;
}

Class_B.h

#import "Class_A.h"

Class_B.m

- (void)viewDidLoad
{
    [super viewDidLoad];

    Class_A *Class_A_Instance = [[Class_A alloc] init];
    NSString *importedString = [Class_A_Instance stringPassage:self];
    [Class_A_Instance release];

    NSLog(@"Received String: %@",importedString);

    // Do any additional setup after loading the view from its nib.
}

嗯，它就像一个魅力！当加载Class_B时，我可以在日志输出中读取“String to pass：A FANTASTIC STRING！”和“收到的字符串：一个神奇的字符串！”;但如果我只改变这部分代码（我需要它！）：

Class_A.m

 - (void)viewDidLoad
{
    [super viewDidLoad];

    stringToPass = @"ANOTHER FANTASTIC STRING!";

        // Do any additional setup after loading the view, typically from a nib.
   }

- (NSString *)stringPassage:(id)sender{
    NSString *string = stringToPass; // here I must call the string FROM another method of Class_A (in this example from - (void)viewDidLoad
    NSLog(@"String to pass: %@",string);
    return string;
}

我可以在日志输出中读取“String to pass：（null）”和obv“Received String：（null）”;它令人难以置信，因为我可以将全局变量* stringToPass完美地传递给Class_A的每个方法，除了这个 - （NSString *）方法。那么问题是什么？谢谢！

Answer 1

在您致电- (void)viewDidLoad之后才会调用{p> -(NSString *)stringPassage。尝试将stringToPass = @"ANOTHER FANTASTIC STRING!";移至-(id)init

的Class_A方法

Answer 2

您正在调用init方法，而不是viewDidLoad方法。

如果你将它添加到Class_A，你会更接近：

-(id) init {
    self = [super init];
    if(self) {
        stringToPass = @"ANOTHER FANTASTIC STRING!";   
    }

    return self;
}

Answer 3

我们有两个viewControllers，即FirstVC和SecondVC。在SecondVC中创建一个字符串，

@interface SecondVC : UIViewController { NSString *string2pass; }

@property (retain, nonatomic) NSString *string2pass;

在FirstVC中，当您要呈现SecondVC时，将字符串传递为

- (void)presentSecondView 
  { 
    SecondVC *secondVC = [[SecondVC alloc]initWithNibName:@"SecondVC" bundle:nil]; 

    secondVC.string2pass = @"this is a passing string";

   [self presentModalViewController:resView animated:YES];

  }    
- (void)viewDidLoad 
  { 
      NSString *string4mFirstVC = string2Pass 
  }

类之间的NSString

3 个答案: