使用委託模式（傳回資料）

要將資料從當前檢視控制器傳遞迴上一個檢視控制器，可以使用委託模式。

此示例假定你已在 Interface Builder 中建立了 segue，並將 segue 識別符號設定為 showSecondViewController。出口和操作還必須連線到以下程式碼中的名稱。

第一檢視控制器

第一檢視控制器的程式碼是

迅速

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 的

@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

請注意我們的自定義 DataEnteredDelegate 協議的使用。

第二檢視控制器和協議

第二個檢視控制器的程式碼是

迅速

// 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 的

@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

請注意，protocol 位於 View Controller 類之外。