Ios 在函数之间传递后数据丢失

关于NSDictionary上丢失的数据（或我试图在视图控制器之间传递的任何数据类型），我在这里遇到了问题。我正在传递数据，我将在下面的代码中显示。但是在传递并再次访问数据之后，我收到了一个

null

对象

FirstViewController.m

-(void)showSecondViewController{
  SecondViewController *secondVC = [SecondViewController new];
  NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
  [passedData setObject:@"First Object" forKey:@"first_obj"];
  [passedData setObject:@"Second Object" forKey:@"second_obj"];
  [secondVC setData:passedData];
  [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

-(void)setData(NSDictionary *)data{
   passedDataContainer = data;
}

-(void)usePassedData{
  NSLog(@"Display Passed Data from FirstViewController: %@",data);
}

在my

SecondViewController.h中

 @interface SecondViewController : UIViewController
{
   NSDictionary *passedDataContainer;
}

-(void)setData(NSDictionary *)data;

@property(strong, nonatomic) NSDictionary *data;

在
SecondViewController.m

-(void)showSecondViewController{
  SecondViewController *secondVC = [SecondViewController new];
  NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
  [passedData setObject:@"First Object" forKey:@"first_obj"];
  [passedData setObject:@"Second Object" forKey:@"second_obj"];
  [secondVC setData:passedData];
  [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

-(void)setData(NSDictionary *)data{
   passedDataContainer = data;
}

-(void)usePassedData{
  NSLog(@"Display Passed Data from FirstViewController: %@",data);
}

由此，我假设我从我的
FirstViewController
中得到了我的
NSDictionary
，但是当我使用它时，比如说

-(void)usePassedData{
  NSLog(@"Display Passed Data from FirstViewController: %@",passedDataContainer);
}

在这个代码段中，输出将是

Display Passed Data from FirstViewController: (null)

我希望我已经很好地解释了这个案例。我已经检查了我在这里找到的一些可能的修复，例如，这篇文章-->。如果我知道这是什么原因，我会很高兴，因为我对Objective-C不熟悉

另外，我正在使用ARC

谢谢。
如果要将数据从secondviewcontroller传递到first view controller，则可以使用自定义委托，使用自定义委托，可以将数据从secondviewcintroller传递到firstviewcontroller

链接可能对您有所帮助。
这是了解学员的链接。
有许多方法可以实现您的解决方案

默认值
代理（自定义）
针对您的问题：
使用对NSDictionary的@PRoperty（Strong）引用，并从FirstViewController使用SecondViewController实例的适当alloc引用它。
尝试这样做，希望这对您有所帮助：）

在您的
SecondViewController.h




   @synthesize data; //just synthesize it

-(void)showSecondViewController{
 SecondViewController *secondVC = [SecondViewController new];
 NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
 [passedData setObject:@"First Object" forKey:@"first_obj"];
 [passedData setObject:@"Second Object" forKey:@"second_obj"];
  secondVC.data = passedData; //[secondVC setData:passedData];//change this
 [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

在
SecondViewController.m

-(void)showSecondViewController{
  SecondViewController *secondVC = [SecondViewController new];
  NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
  [passedData setObject:@"First Object" forKey:@"first_obj"];
  [passedData setObject:@"Second Object" forKey:@"second_obj"];
  [secondVC setData:passedData];
  [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

-(void)setData(NSDictionary *)data{
   passedDataContainer = data;
}

-(void)usePassedData{
  NSLog(@"Display Passed Data from FirstViewController: %@",data);
}



   @synthesize data; //just synthesize it

-(void)showSecondViewController{
 SecondViewController *secondVC = [SecondViewController new];
 NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
 [passedData setObject:@"First Object" forKey:@"first_obj"];
 [passedData setObject:@"Second Object" forKey:@"second_obj"];
  secondVC.data = passedData; //[secondVC setData:passedData];//change this
 [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}



   @synthesize data; //just synthesize it

-(void)showSecondViewController{
 SecondViewController *secondVC = [SecondViewController new];
 NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
 [passedData setObject:@"First Object" forKey:@"first_obj"];
 [passedData setObject:@"Second Object" forKey:@"second_obj"];
  secondVC.data = passedData; //[secondVC setData:passedData];//change this
 [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

和您的
FirstViewController.m

-(void)showSecondViewController{
  SecondViewController *secondVC = [SecondViewController new];
  NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
  [passedData setObject:@"First Object" forKey:@"first_obj"];
  [passedData setObject:@"Second Object" forKey:@"second_obj"];
  [secondVC setData:passedData];
  [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

-(void)setData(NSDictionary *)data{
   passedDataContainer = data;
}

-(void)usePassedData{
  NSLog(@"Display Passed Data from FirstViewController: %@",data);
}



   @synthesize data; //just synthesize it

-(void)showSecondViewController{
 SecondViewController *secondVC = [SecondViewController new];
 NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
 [passedData setObject:@"First Object" forKey:@"first_obj"];
 [passedData setObject:@"Second Object" forKey:@"second_obj"];
  secondVC.data = passedData; //[secondVC setData:passedData];//change this
 [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}


根据您的解释，您正在使用
故事板序列
从
第一视图控制器
转换到
第二视图控制器
。您需要以
prepareforsgue
方法而不是
showSecondViewController
方法传递数据

   @synthesize data; //just synthesize it

-(void)showSecondViewController{
 SecondViewController *secondVC = [SecondViewController new];
 NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
 [passedData setObject:@"First Object" forKey:@"first_obj"];
 [passedData setObject:@"Second Object" forKey:@"second_obj"];
  secondVC.data = passedData; //[secondVC setData:passedData];//change this
 [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

试试这个

FirstViewController.m

-(void)showSecondViewController{

  [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
     if ([segue.identifier isEqualToString:@"SecondViewControllerSegue"]){
     NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
     [passedData setObject:@"First Object" forKey:@"first_obj"];
     [passedData setObject:@"Second Object" forKey:@"second_obj"];

     SecondViewController *secondVC = (SecondViewController *)segue.destinationViewController;
    [secondVC setData:passedData];
}

在
SecondViewController.h

 @interface SecondViewController : UIViewController
{
   NSDictionary *passedDataContainer;
}

-(void)setData(NSDictionary *)data;

@property(strong, nonatomic) NSDictionary *data;

在
SecondViewController.m中

-(void)showSecondViewController{
  SecondViewController *secondVC = [SecondViewController new];
  NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
  [passedData setObject:@"First Object" forKey:@"first_obj"];
  [passedData setObject:@"Second Object" forKey:@"second_obj"];
  [secondVC setData:passedData];
  [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

-(void)setData(NSDictionary *)data{
   passedDataContainer = data;
}

-(void)usePassedData{
  NSLog(@"Display Passed Data from FirstViewController: %@",data);
}

为什么不使用属性？此教程链接可能会帮助您：