从委托视图向委托视图发送数据[Objective-C]

Question

So I am trying to learn how to send data from one view controller to another.

My code thus far takes the data entered from one VC ( DelegateVC ) and displays it in a label on another VC( ViewController ).

Here the delegate is ViewController and the delegated is DelegateVC .

===========================================================================

Main Question

But what if I want to pass the data of the label from ViewController to DelegateVC ? How can I accomplish this? I tried engineering the same concept of delegates but with the DelegateVC as the delegate of ViewController . Not sure if this is the write approach.

TL;DR:

In VC , if I hit Next View , I go to DelegateVC and enter "test", it will show up in VC's receiving label as "test".

Now the next time I hit Next View , I want the existing label's value to show up in the TextField of DelegateVC . Instead of a blank TextField , there will be the value "test".

=========================================================================== Let's say I have a Main.storyboard like so:

I have a ViewController.h file as:

#import <UIKit/UIKit.h>
@interface ViewController : UIViewController


@end

ViewController.m :

#import "ViewController.h"
#import "DelegatedVC.h"

@interface ViewController () <MainVCDelegate>
@property (strong, nonatomic) IBOutlet UILabel *receivingLabel;
- (IBAction)nextView:(id)sender;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}


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


- (IBAction)nextView:(id)sender {

}

-(void) sendBackData:(DelegatedVC *)delegatedVC :(NSString *)textField {
    [delegatedVC dismissViewControllerAnimated:YES completion:nil];
    self.receivingLabel.text = textField;
}
-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    DelegatedVC *secondVC = segue.destinationViewController;
    secondVC.delegate = self;
}
@end

DelegateVC.h:

#import <UIKit/UIKit.h>
@protocol MainVCDelegate;

@interface DelegatedVC : UIViewController
@property (strong, nonatomic) IBOutlet UITextField *sendDataTF;
- (IBAction)sendData:(id)sender;
@property (weak, nonatomic) id<MainVCDelegate> delegate;
@end

@protocol MainVCDelegate <NSObject>
-(void) sendBackData: (DelegatedVC *) delegatedVC : (NSString *) textField;
@end

DelegateVC.m:

#import "DelegatedVC.h"
@protocol MainVCDelegate;

@interface DelegatedVC ()

@end

@implementation DelegatedVC

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
}

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

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

- (IBAction)sendData:(id)sender {
    [self.delegate sendBackData: self : _sendDataTF.text];
}
@end

Answer 1

But what if I want to pass the data of the label from ViewController to DelegateVC? How can I accomplish this?

So you're doing the delegation right as I can see in your code. Back to your main question, you just need to declare a public NSString object in your DelegateVC.h , and then access that and pass the data to that from your ViewController 's prepareForSegue .

Next step, in your DelegateVC.m , get your NSString object's value and pass it to your UITextField .

Let me know if this helps :)

Answer 2

A delegate allows one object to send messages to another object when an event happens.

In your case to pass data of label from ViewController to DelegateVC , you do not need to use delegate. But since you want to update receivingLabel when changing happens on sendDataTF textfield , in this case you need a delegate and I think you have done it well.

Solution : You need to declare a property in DelegateVC to store passing string from ViewController and set that text in sendDataTF on viewDidLoad .

Declare a property in DelegateVC.h:

@interface DelegatedVC : UIViewController

@property (weak, nonatomic) id<MainVCDelegate> delegate;
@property (strong, nonatomic) NSString *labelString;

@property (strong, nonatomic) IBOutlet UITextField *sendDataTF;

- (IBAction)sendData:(id)sender;

@end

Pass receivingLabel text in ViewController.m:

-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender           
{
   DelegatedVC *secondVC = segue.destinationViewController;
   secondVC.delegate = self;
   secondVC.labelString = self.receivingLabel.text;
}

Set labelString in DelegateVC.m:

- (void)viewDidLoad {
  [super viewDidLoad];
  self.sendDataTF.text = self.labelString;
}

Hope it will work.

Answer 3

Here is proper working code you can have a look at :

DelegateVc.h File with Label and button

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

@interface DelegateVC : UIViewController
@property (weak, nonatomic) IBOutlet UILabel *ReceiveLabel;
@property (weak, nonatomic) IBOutlet UIButton *NextView;
@property (strong, nonatomic) NSString *TextFeildText;

DelegateVC.m File With segues

-(void)viewWillAppear:(BOOL)animated{
    _ReceiveLabel.text = _TextFeildText;
}
- (IBAction)NextViewBtnAction:(id)sender {
    [self performSegueWithIdentifier:@"ToDelegated" sender:sender];
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    // Make sure your segue name in storyboard is the same as this line
    if ([[segue identifier] isEqualToString:@"ToDelegated"])
    {
        // Get reference to the destination view controller
        DelegatedVC *vc = [segue destinationViewController];
        vc.LabelText = _ReceiveLabel.text;

        // Pass any objects to the view controller here, like...

    }
}

DelagatedVc.h with textfield

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

@interface DelegatedVC : UIViewController
@property (weak, nonatomic) IBOutlet UITextField *RCTextField;
@property (weak, nonatomic) IBOutlet UIButton *SenddataBtn;
@property (strong, nonatomic) NSString *LabelText;
@end

DelagatedVc.m with Segue

-(void)viewWillAppear:(BOOL)animated{
    _RCTextField.text = _LabelText;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (IBAction)SendDataBtnAction:(id)sender {
    [self performSegueWithIdentifier:@"ToDelegate" sender:sender];
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    // Make sure your segue name in storyboard is the same as this line
    if ([[segue identifier] isEqualToString:@"ToDelegate"])
    {
        // Get reference to the destination view controller
        DelegateVC *vc = [segue destinationViewController];
        // Pass any objects to the view controller here, like...
        vc.TextFeildText = _RCTextField.text;


    }
}

My storyBoard Outlook