【OC】多界面传值
属性传值
属性的传值一般来说是从前往后进行的
这个的实现比较简单，我们可以在视图A之中实现一个 事件 ，然后将信息发送给后一个视图B并且控制视图弹出。以下是我用searchBar完成的一个界面传值功能，当我们在控制器A之中点击搜索时，就会将searchBar之中的文字内容通过控制器B的属性传给控制器B，实现了属性传值
#import "ViewController.h"
#import "ViewController2.h"
@interface ViewController () <UISearchBarDelegate>
@property (nonatomic, strong)UISearchBar *searchBar;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.searchBar = [[UISearchBar alloc] init];
self.searchBar.frame = CGRectMake(100, 100, 200, 200);
self.searchBar.delegate = self;
[self.view addSubview:self.searchBar];
}
-(void)searchBarSearchButtonClicked:(UISearchBar *)searchBar{
NSLog(@"1");
ViewController2* controller2 = [[ViewController2 alloc] init];
controller2.text = searchBar.text;
[self presentViewController:controller2 animated:YES completion:nil];
}
-(void) touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
[self.searchBar resignFirstResponder];
}
@end
#import <UIKit/UIKit.h>
NS_ASSUME_NONNULL_BEGIN
@interface ViewController2 : UIViewController
@property (nonatomic,strong)NSString* text;
@end
NS_ASSUME_NONNULL_END
#import "ViewController2.h"
@interface ViewController2 ()
@end
@implementation ViewController2
- (void)viewDidLoad {
[super viewDidLoad];
self.view.backgroundColor = [UIColor redColor];
UILabel* label = [[UILabel alloc] init];
label.text = self.text;
label.frame = CGRectMake(100, 100, 200, 200);
[self.view addSubview:label];
}
协议/代理传值
原理：B 持有一个 delegate 属性（类型为协议），A 实现该协议并将自己赋值给 B 的 delegate。B 需要传值时调用 delegate 方法，A 就能接收到数据
// 1. 定义协议（通常写在 B 的头文件）
@protocol BDelegate <NSObject>
- (void)didSelectValue:(NSString *)value;
@end
// 2. B 持有 delegate（必须用 weak）
@property (nonatomic, weak) id<BDelegate> delegate;
// 3. B 中触发
[self.delegate didSelectValue:@"hello"];
// 4. A 实现协议
- (void)didSelectValue:(NSString *)value {
NSLog(@"收到: %@", value);
}
delegate 必须声明为 weak，否则 A 持有 B、B 又强持有 A，造成循环引用内存泄漏。
Demo:
CityListViewController.h（B 页面头文件）
#import <UIKit/UIKit.h>
// 1. 定义协议
@protocol CityListDelegate <NSObject>
- (void)cityListViewController:(UIViewController *)vc didSelectCity:(NSString *)city;
@end
@interface CityListViewController : UIViewController
// 2. 声明 delegate 属性（必须用 weak）
@property (nonatomic, weak) id<CityListDelegate> delegate;
@end
CityListViewController.m（B 页面实现）
#import "CityListViewController.h"
@interface CityListViewController () <UITableViewDataSource, UITableViewDelegate>
@property (nonatomic, strong) UITableView *tableView;
@property (nonatomic, strong) NSArray<NSString *> *cities;
@end
@implementation CityListViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.title = @"选择城市";
self.view.backgroundColor = [UIColor systemBackgroundColor];
self.cities = @[@"北京", @"上海", @"广州", @"深圳", @"成都"];
self.tableView = [[UITableView alloc] initWithFrame:self.view.bounds style:UITableViewStyleInsetGrouped];
self.tableView.dataSource = self;
self.tableView.delegate = self;
[self.view addSubview:self.tableView];
}
#pragma mark - UITableViewDataSource
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return self.cities.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cell"];
if (!cell) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"cell"];
}
cell.textLabel.text = self.cities[indexPath.row];
return cell;
}
#pragma mark - UITableViewDelegate
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
[tableView deselectRowAtIndexPath:indexPath animated:YES];
NSString *selectedCity = self.cities[indexPath.row];
// 3. 调用 delegate 方法，将城市名传回去
if ([self.delegate respondsToSelector:@selector(cityListViewController:didSelectCity:)]) {
[self.delegate cityListViewController:self didSelectCity:selectedCity];
}
[self.navigationController popViewControllerAnimated:YES];
}
@end
ViewController.m（A 页面实现）
#import "ViewController.h"
#import "CityListViewController.h"
// 4. A 遵守协议
@interface ViewController () <CityListDelegate>
@property (nonatomic, strong) UILabel *cityLabel;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.title = @"代理传值";
self.view.backgroundColor = [UIColor systemBackgroundColor];
// 城市 Label
self.cityLabel = [[UILabel alloc] initWithFrame:CGRectMake(40, 200, self.view.bounds.size.width - 80, 50)];
self.cityLabel.text = @"请选择城市";
self.cityLabel.textAlignment = NSTextAlignmentCenter;
self.cityLabel.font = [UIFont systemFontOfSize:20 weight:UIFontWeightMedium];
[self.view addSubview:self.cityLabel];
// 跳转按钮
UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
button.frame = CGRectMake(100, 280, self.view.bounds.size.width - 200, 44);
[button setTitle:@"选择城市" forState:UIControlStateNormal];
button.titleLabel.font = [UIFont systemFontOfSize:17];
[button addTarget:self action:@selector(pushToCityList) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:button];
}
- (void)pushToCityList {
CityListViewController *cityVC = [[CityListViewController alloc] init];
// 5. 设置 delegate 为 self（A 自己）
cityVC.delegate = self;
[self.navigationController pushViewController:cityVC animated:YES];
}
#pragma mark - CityListDelegate
// 6. 实现协议方法，接收传回的城市名
- (void)cityListViewController:(UIViewController *)vc didSelectCity:(NSString *)city {
self.cityLabel.text = city;
}
@end
block传值
原理：B 声明一个 block 属性，A 在跳转到 B 之前赋值这个 block。B 需要传值时调用这个 block，回调直接在 A 的闭包里执行。
// 1. B 声明 block 属性
@property (nonatomic, copy) void(^valueBlock)(NSString *value);
// 2. A 赋值 block
B *bVC = [[B alloc] init];
bVC.valueBlock = ^(NSString *value) {
NSLog(@"收到: %@", value);
};
// 3. B 中触发
if (self.valueBlock) {
self.valueBlock(@"hello");
}
关键：若 block 内部引用了 self，需要用 __weak typeof(self) weakSelf = self; 避免循环引用。block 属性要用 copy 修饰。
B 页面声明一个 block 属性，A 跳转前赋值 block，B 选择城市后调用 block 回调。
CityListViewController.h（B 页面头文件）
objc#import <UIKit/UIKit.h>
@interface CityListViewController : UIViewController
// 1. 声明 block 属性（用 copy 修饰）
@property (nonatomic, copy) void(^selectCityBlock)(NSString *city);
@end
CityListViewController.m（B 页面实现）
objc#import "CityListViewController.h"
@interface CityListViewController () <UITableViewDataSource, UITableViewDelegate>
@property (nonatomic, strong) UITableView *tableView;
@property (nonatomic, strong) NSArray<NSString *> *cities;
@end
@implementation CityListViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.title = @"选择城市";
self.view.backgroundColor = [UIColor systemBackgroundColor];
self.cities = @[@"北京", @"上海", @"广州", @"深圳", @"成都"];
self.tableView = [[UITableView alloc] initWithFrame:self.view.bounds style:UITableViewStyleInsetGrouped];
self.tableView.dataSource = self;
self.tableView.delegate = self;
[self.view addSubview:self.tableView];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return self.cities.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cell"];
if (!cell) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"cell"];
}
cell.textLabel.text = self.cities[indexPath.row];
return cell;
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
[tableView deselectRowAtIndexPath:indexPath animated:YES];
NSString *selectedCity = self.cities[indexPath.row];
// 2. 调用 block，将城市名回传
if (self.selectCityBlock) {
self.selectCityBlock(selectedCity);
}
[self.navigationController popViewControllerAnimated:YES];
}
@end
ViewController.m（A 页面实现）
objc#import "ViewController.h"
#import "CityListViewController.h"
@interface ViewController ()
@property (nonatomic, strong) UILabel *cityLabel;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.title = @"Block 传值";
self.view.backgroundColor = [UIColor systemBackgroundColor];
self.cityLabel = [[UILabel alloc] initWithFrame:CGRectMake(40, 200, self.view.bounds.size.width - 80, 50)];
self.cityLabel.text = @"请选择城市";
self.cityLabel.textAlignment = NSTextAlignmentCenter;
self.cityLabel.font = [UIFont systemFontOfSize:20 weight:UIFontWeightMedium];
[self.view addSubview:self.cityLabel];
UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
button.frame = CGRectMake(100, 280, self.view.bounds.size.width - 200, 44);
[button setTitle:@"选择城市" forState:UIControlStateNormal];
button.titleLabel.font = [UIFont systemFontOfSize:17];
[button addTarget:self action:@selector(pushToCityList) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:button];
}
- (void)pushToCityList {
CityListViewController *cityVC = [[CityListViewController alloc] init];
// 3. 赋值 block，__weak 避免循环引用
__weak typeof(self) weakSelf = self;
cityVC.selectCityBlock = ^(NSString *city) {
weakSelf.cityLabel.text = city;
};
[self.navigationController pushViewController:cityVC animated:YES];
}
@end
通知传值（NSNotification）
原理：发送者 post 一条通知到通知中心，所有注册了该通知名的观察者都会收到，实现一对多广播。
// 1. 观察者注册（A 或任意对象）
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(handleNoti:)
name:@"MyNotification"
object:nil];
// 2. 发送通知（B 或任意位置）
[[NSNotificationCenter defaultCenter] postNotificationName:@"MyNotification"
object:nil
userInfo:@{@"key": @"hello"}];
// 3. 处理通知
- (void)handleNoti:(NSNotification *)noti {
NSString *value = noti.userInfo[@"key"];
}
// 4. 移除观察者（dealloc 中！）
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
⚠️ 关键：必须在 dealloc 中移除观察者，否则对象销毁后若收到通知会崩溃（野指针）。iOS 9+ 系统会自动移除，但手动移除更安全。
页面选择城市后发送通知，A 页面注册监听该通知并接收城市名，实现跨层/跨模块传值。
NotificationNames.h（通知名常量，推荐单独定义）
objc#ifndef NotificationNames_h
#define NotificationNames_h
static NSString * const kSelectCityNotification = @"kSelectCityNotification";
static NSString * const kSelectCityKey = @"city";
#endif
CityListViewController.m（B 页面实现）
objc#import "CityListViewController.h"
#import "NotificationNames.h"
@interface CityListViewController () <UITableViewDataSource, UITableViewDelegate>
@property (nonatomic, strong) UITableView *tableView;
@property (nonatomic, strong) NSArray<NSString *> *cities;
@end
@implementation CityListViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.title = @"选择城市";
self.view.backgroundColor = [UIColor systemBackgroundColor];
self.cities = @[@"北京", @"上海", @"广州", @"深圳", @"成都"];
self.tableView = [[UITableView alloc] initWithFrame:self.view.bounds style:UITableViewStyleInsetGrouped];
self.tableView.dataSource = self;
self.tableView.delegate = self;
[self.view addSubview:self.tableView];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return self.cities.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cell"];
if (!cell) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"cell"];
}
cell.textLabel.text = self.cities[indexPath.row];
return cell;
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
[tableView deselectRowAtIndexPath:indexPath animated:YES];
NSString *selectedCity = self.cities[indexPath.row];
// 发送通知，将城市名放入 userInfo
[[NSNotificationCenter defaultCenter]
postNotificationName:kSelectCityNotification
object:nil
userInfo:@{kSelectCityKey: selectedCity}];
[self.navigationController popViewControllerAnimated:YES];
}
@end
ViewController.m（A 页面实现）
objc#import "ViewController.h"
#import "NotificationNames.h"
@interface ViewController ()
@property (nonatomic, strong) UILabel *cityLabel;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.title = @"通知传值";
self.view.backgroundColor = [UIColor systemBackgroundColor];
self.cityLabel = [[UILabel alloc] initWithFrame:CGRectMake(40, 200, self.view.bounds.size.width - 80, 50)];
self.cityLabel.text = @"请选择城市";
self.cityLabel.textAlignment = NSTextAlignmentCenter;
self.cityLabel.font = [UIFont systemFontOfSize:20 weight:UIFontWeightMedium];
[self.view addSubview:self.cityLabel];
UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
button.frame = CGRectMake(100, 280, self.view.bounds.size.width - 200, 44);
[button setTitle:@"选择城市" forState:UIControlStateNormal];
button.titleLabel.font = [UIFont systemFontOfSize:17];
[button addTarget:self action:@selector(pushToCityList) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:button];
// 注册通知监听
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:@selector(handleSelectCity:)
name:kSelectCityNotification
object:nil];
}
- (void)pushToCityList {
CityListViewController *cityVC = [[CityListViewController alloc] init];
[self.navigationController pushViewController:cityVC animated:YES];
}
// 接收通知
- (void)handleSelectCity:(NSNotification *)notification {
NSString *city = notification.userInfo[kSelectCityKey];
self.cityLabel.text = city;
}
// 必须移除观察者！
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
@end
KVO（键值观察）
原理：观察者注册监听某个对象的某个属性，当该属性值发生变化时，系统会自动调用观察者的回调方法，不需要任何主动通知代码。
// 1. 观察者注册监听
[model addObserver:self
forKeyPath:@"name"
options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld
context:nil];
// 2. 属性变化时自动回调
- (void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context {
if ([keyPath isEqualToString:@"name"]) {
NSString *newValue = change[NSKeyValueChangeNewKey];
NSLog(@"name 变成了: %@", newValue);
}
}
// 3. dealloc 中必须移除！
- (void)dealloc {
[model removeObserver:self forKeyPath:@"name"];
}
⚠️ 关键：必须在 dealloc 中调用 removeObserver:forKeyPath:，否则会崩溃。在 Swift 中推荐使用 Combine 或 @Published 代替 KVO。
由于笔者还没有深入学习KVO在此先不给出KVO的具体demo，学完KVO再回来补全