如何使用委托/協議在多個視圖控制器之間傳遞值

Question

基本上，我現在打算使用委托在視圖控制器之間傳遞值。

視圖控制器的流是A-> B-> C

當用戶在“ C”視圖控制器中執行某些操作時，如何將值傳遞回第一個視圖控制器“ A”？

在我自己的代碼中，委托方法永遠不會觸發，並且“ self.delegate”始終為“ null”。 我不確定為什么以及如何解決這個問題。

下面是第一個VC和第三個VC的代碼：

#import "ViewController.h"
#import "ThirdViewController.h"

@interface ViewController ()<PassValueProtocal>
@property (weak, nonatomic) IBOutlet UILabel *myLabel;

@end

@implementation ViewController
{
    ThirdViewController *thirdVC;
}

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

- (void) passValueBack:(NSString *)value
{
    NSLog(@"HAHAH");
}

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


- (IBAction)segueToSecondVC:(UIButton *)sender
{
    thirdVC = [ThirdViewController sharedManager];
    thirdVC.delegate = self;
}

@end

#import "ThirdViewController.h"

@interface ThirdViewController ()
@property (weak, nonatomic) IBOutlet UITextField *myTextField;

@end

@implementation ThirdViewController

+ (id) sharedManager
{
    NSLog(@"myDelegate sharedManager");
    static ThirdViewController *sharedManager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{ sharedManager = [[self alloc] init]; });
    return sharedManager;
}

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

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

- (IBAction)passValueAction:(UIButton *)sender
{
    NSLog(@"%@", self.delegate);
    if ([self.delegate respondsToSelector:@selector(passValueBack:)])
    {
        [self.delegate passValueBack:self.myTextField.text];
    }
}

Answer 1

上面的代碼沒有顯示您在UIViewController哪里設置委托。 這可能是為什么它為nil以及為什么永遠不會觸發您的委托方法的原因。 在初始化UIViewController但在像這樣推送它之前設置委托屬性：

// Inside your third viewcontroller class:
@interface ThirdViewController ()
@property (weak, nonatomic) id delegate; // make sure the delegate is set to weak
@end


// Maybe in your AppDelegate, before you push the third view controller
ThirdViewController *thirdVC = [[ThirdViewController alloc] init];
thirdVC.delegate = self;
// Now push the VC. The below assumes a UINavigationController but that detail isn't important.
[self.navigationController pushViewController:thirdVC animated:YES];

Answer 2

是的，有可能做。 為了從C-> A傳回數據，您需要鏈接代表

這是情節提要的外觀： http : //i.imgur.com/9PXdlno.png?1

在情節提要中注意標記標識符

FirstViewController：

import UIKit

class FirstViewController: UIViewController, SecondViewControllerDelegate {

    @IBAction func buttonPressed(sender: AnyObject) {
        performSegueWithIdentifier("goToSecondView", sender: self)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if(segue.identifier == "goToSecondView"){
            let secondVC: SecondViewController = segue.destinationViewController as! SecondViewController

            secondVC.delegate = self
        }
    }

    func speakSecond(name: String) {
        print("Data from Third view is: \(name)")
    }
}

SecondViewController：

import UIKit

protocol SecondViewControllerDelegate{
    func speakSecond(name: String)
}


class SecondViewController: UIViewController, ThirdViewControllerDelegate {

    var delegate: SecondViewControllerDelegate?

    @IBAction func buttonPressed(sender: AnyObject) {
        performSegueWithIdentifier("goToThirdView", sender: self)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if(segue.identifier == "goToThirdView"){
            let thirdVC: ThirdViewController = segue.destinationViewController as! ThirdViewController
            thirdVC.delegate = self
        }
    }

    func speakThird(name: String) {
        delegate?.speakSecond(name)
    }
}

ThirdViewController：

import UIKit

protocol ThirdViewControllerDelegate{
    func speakThird(name: String)
}

class ThirdViewController: UIViewController {

    var delegate: ThirdViewControllerDelegate?

    @IBOutlet var textField: UITextField!

    @IBAction func buttonPressed(sender: AnyObject) {
        let text = textField.text
        delegate?.speakThird(text)
        self.navigationController?.popToRootViewControllerAnimated(true)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

}