iOS Passing Data between View Controllers Using the Delegate Pattern (passing data back)
Example
To pass data from the current view controller back to the previous view controller, you can use the delegate pattern.
This example assumes that you have made a segue in the Interface Builder and that you set the segue identifier to showSecondViewController. The outlets and actions must also be hooked up to the names in the following code.
First View Controller
The code for the First View Controller is
Swift
class FirstViewController: UIViewController, DataEnteredDelegate {
@IBOutlet weak var label: UILabel!
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "showSecondViewController", let secondViewController = segue.destinationViewController as? SecondViewController {
secondViewController.delegate = self
}
}
// required method of our custom DataEnteredDelegate protocol
func userDidEnterInformation(info: String) {
label.text = info
navigationController?.popViewControllerAnimated(true)
}
}
Objective-C
@interface FirstViewController : UIViewController <DataEnteredDelegate>
@property (weak, nonatomic) IBOutlet UILabel *label;
@end
@implementation FirstViewController
- (void)viewDidLoad {
[super viewDidLoad];
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
SecondViewController *secondViewController = segue.destinationViewController;
secondViewController.delegate = self;
}
-(void)userDidEnterInformation:(NSString *)info {
_label.text = info
[self.navigationController popViewControllerAnimated:YES];
}
@end
Note the use of our custom DataEnteredDelegate protocol.
Second View Controller and Protocol
The code for the second view controller is
Swift
// protocol used for sending data back
protocol DataEnteredDelegate: class {
func userDidEnterInformation(info: String)
}
class SecondViewController: UIViewController {
// making this a weak variable so that it won't create a strong reference cycle
weak var delegate: DataEnteredDelegate?
@IBOutlet weak var textField: UITextField!
@IBAction func sendTextBackButton(sender: AnyObject) {
// call this method on whichever class implements our delegate protocol (the first view controller)
delegate?.userDidEnterInformation(textField.text ?? "")
}
}
Objective-C
@protocol DataEnteredDelegate <NSObject>
-(void)userDidEnterInformation:(NSString *)info;
@end
@interface SecondViewController : UIViewController
@property (nonatomic) id <DataEnteredDelegate> delegate;
@property (weak, nonatomic) IBOutlet UITextField *textField;
@end
@implementation SecondViewController
- (void)viewDidLoad {
[super viewDidLoad];
}
- (IBAction) sendTextBackButton:(id)sender{
[_delegate userDidEnterInformation:textField.text];
}
@end
Note that the protocol is outside of the View Controller class.
