在视图控制器之间传递数据

在iOS开发中，视图控制器之间的数据传递是一个常见需求。本文将详细介绍多种在视图控制器间传递数据的方法，包括正向传递、反向传递等。

正向传递数据

直接设置属性

若要将数据从一个视图控制器传递到另一个视图控制器，可直接设置目标视图控制器的属性。以下是示例代码：

// ViewControllerB.h
@interface ViewControllerB : UIViewController
@property (nonatomic, assign) BOOL isSomethingEnabled;
@end

// ViewControllerA.m
#import "ViewControllerB.h"
- (void)loadViewControllerB {
    ViewControllerB *viewControllerB = [[ViewControllerB alloc] initWithNib:@"ViewControllerB" bundle:nil];
    viewControllerB.isSomethingEnabled = YES;
    [self.navigationController pushViewController:viewControllerB animated:YES];
}

使用Segue传递

若使用Storyboards，可利用Segue正向传递数据。示例如下：

// ViewControllerB.h
@interface ViewControllerB : UIViewController
@property (nonatomic, assign) BOOL isSomethingEnabled;
@end

// ViewControllerA.m
#import "ViewControllerB.h"
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:@"showDetailSegue"]) {
        ViewControllerB *controller = (ViewControllerB *)segue.destinationViewController;
        controller.isSomethingEnabled = YES;
    }
}

反向传递数据

使用协议和代理

为实现从ViewControllerB向ViewControllerA反向传递数据，可使用协议和代理。示例代码如下：

// ViewControllerB.h
@class ViewControllerB;
@protocol ViewControllerBDelegate <NSObject>
- (void)addItemViewController:(ViewControllerB *)controller didFinishEnteringItem:(NSString *)item;
@end

@interface ViewControllerB : UIViewController
@property (nonatomic, weak) id <ViewControllerBDelegate> delegate;
@end

// ViewControllerB.m
- (void)popViewController {
    NSString *itemToPassBack = @"Pass this value back to ViewControllerA";
    [self.delegate addItemViewController:self didFinishEnteringItem:itemToPassBack];
    [self.navigationController popViewControllerAnimated:YES];
}

// ViewControllerA.h
#import "ViewControllerB.h"
@interface ViewControllerA : UIViewController <ViewControllerBDelegate>
@end

// ViewControllerA.m
- (void)addItemViewController:(ViewControllerB *)controller didFinishEnteringItem:(NSString *)item {
    NSLog(@"This was returned from ViewControllerB %@", item);
}

// 在ViewControllerA中推送ViewControllerB时设置代理
- (void)pushViewControllerB {
    ViewControllerB *viewControllerB = [[ViewControllerB alloc] initWithNib:@"ViewControllerB" bundle:nil];
    viewControllerB.delegate = self;
    [[self navigationController] pushViewController:viewControllerB animated:YES];
}

使用Block

Block是匿名函数，也可用于反向传递数据。示例如下：

// ControllerA.h
@property void(^selectedVoucherBlock)(NSString *);

// ControllerA.m
- (void)viewDidLoad {
    [super viewDidLoad];
    __unsafe_unretained typeof(self) weakSelf = self;
    self.selectedVoucherBlock = ^(NSString *voucher) {
        weakSelf->someLabel.text = voucher;
    };
}

// 推送ControllerB
- (void)pushToControllerB {
    ControllerB *vc = [[ControllerB alloc] initWithNib:@"ControllerB" bundle:nil];
    vc.sourceVC = self;
    [self.navigationController pushViewController:vc animated:NO];
}

// ControllerB.m
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    NSString *voucher = vouchersArray[indexPath.row];
    if (sourceVC.selectVoucherBlock) {
        sourceVC.selectVoucherBlock(voucher);
    }
    [self.navigationController popToViewController:sourceVC animated:YES];
}

使用NSNotificationCenter传递数据

可使用NSNotificationCenter在不同类之间传递数据。示例如下：

// 注册观察者
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleDeepLinking:) name:@"handleDeepLinking" object:nil];

// 处理通知
- (void)handleDeepLinking:(NSNotification *) notification {
    id someObject = notification.object;
}

// 发布通知
id someObject;
[NSNotificationCenter.defaultCenter postNotificationName:@"handleDeepLinking" object:someObject];

Swift实现示例

正向传递数据

// FirstViewController.swift
import UIKit

class FirstViewController: UIViewController {
    @IBOutlet weak var textField: UITextField!

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "showSecondViewController" {
            let secondViewController = segue.destination as! SecondViewController
            secondViewController.receivedString = textField.text!
        }
    }
}

// SecondViewController.swift
import UIKit

class SecondViewController: UIViewController {
    @IBOutlet weak var label: UILabel!
    var receivedString = ""

    override func viewDidLoad() {
        super.viewDidLoad()
        label.text = receivedString
    }
}

反向传递数据

// FirstViewController.swift
import UIKit

class FirstViewController: UIViewController, DataEnteredDelegate {
    @IBOutlet weak var label: UILabel!

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "showSecondViewController" {
            let secondViewController = segue.destination as! SecondViewController
            secondViewController.delegate = self
        }
    }

    func userDidEnterInformation(info: String) {
        label.text = info
    }
}

// SecondViewController.swift
import UIKit

protocol DataEnteredDelegate: AnyObject {
    func userDidEnterInformation(info: String)
}

class SecondViewController: UIViewController {
    weak var delegate: DataEnteredDelegate? = nil
    @IBOutlet weak var textField: UITextField!

    @IBAction func sendTextBackButton(sender: AnyObject) {
        delegate?.userDidEnterInformation(info: textField.text!)
        _ = self.navigationController?.popViewController(animated: true)
    }
}