将数据从子模态视图传递到父视图控制器的最佳方式是什么?
我有一个子模态登录屏幕在我的iPad应用程序，我想传递回用户信息的父分屏视图控制器。
我正在考虑使用NSNotification，但我不确定这是否是最简单/最有效的方式来传递数据回父。
谢谢!艾伦。
我建议像iPatel那样使用委托来解决您的问题。父视图控制器和登录视图控制器之间的关系使得这种模式合适。当一个对象为了完成特定的职责而创建另一个对象时，应该将委托视为使被创建对象与创建者进行通信的一种方式。选择委托的一个特别令人信服的理由是，如果要完成的任务可能有多个步骤，需要对象之间的高级交互。你可以看看NSURLConnectionDelegate协议作为例证。连接到URL是一项复杂的任务，涉及处理响应、满足身份验证挑战、保存下载的数据和处理错误等阶段，连接和委托在连接的生命周期内共同处理这些问题。
你可能已经注意到，在Objective-C协议是用来实现委托没有紧密耦合创建的对象(在这种情况下你的登录视图控制器)到创建它的对象(父视图控制器)。然后，登录视图控制器可以与任何可以接收在其协议中定义的消息的对象进行交互，而不是依赖于任何特定的类实现。明天，如果你收到一个要求，允许任何视图控制器显示登录视图，登录视图控制器将不需要改变。你的其他视图控制器可以实现它的委托协议，创建和呈现登录视图，并将自己分配为委托，而登录视图控制器永远不会知道它们的存在。
你在Stack Overflow上找到的一些委托示例可能非常令人困惑，与内置框架中的委派示例非常不同。必须仔细选择协议的名称和接口，以及分配给每个对象的职责，以便最大限度地重用代码并实现代码的目标。
你应该首先看一下内置框架中的许多委托协议，以了解在代码中表达的关系是什么样子的。下面是基于您的登录用例的另一个小示例。我希望您会发现委托的目的是明确的，所涉及的对象的角色和职责是明确的，并通过代码中的名称来表达。首先，让我们看看LoginViewController的委托协议:
#import <UIKit/UIKit.h>
@protocol LoginViewControllerDelegate;
@interface LoginViewController : UIViewController
// We choose a name here that expresses what object is doing the delegating
@property (nonatomic, weak) id<LoginViewControllerDelegate> delegate;
@end
@protocol LoginViewControllerDelegate <NSObject>
// The methods declared here are all optional
@optional
// We name the methods here in a way that explains what the purpose of each message is
// Each takes a LoginViewController as the first argument, allowing one object to serve
// as the delegate of many LoginViewControllers
- (void)loginViewControllerDidLoginSuccessfully:(LoginViewController *)lvc;
- (void)loginViewController:(LoginViewController *)lvc didFailWithError:(NSError *)error;
- (void)loginViewControllerDidReceivePasswordResetRequest:(LoginViewController *)lvc;
- (void)loginViewControllerDiDReceiveSignupRequest:(LoginViewController *)lvc;
- (BOOL)loginViewControllerShouldAllowAnonymousLogin:(LoginViewController *)lvc;
@end
登录控制器可以与它的委托通信许多事件，也可以向它的委托询问用于自定义其行为的信息。它在实现中将事件作为对用户操作响应的一部分传递给委托:
#import "LoginViewController.h"
@interface LoginViewController ()
@property (weak, nonatomic) IBOutlet UIButton *anonSigninButton;
@end
@implementation LoginViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Here we ask the delegate for information used to layout the view
BOOL anonymousLoginAllowed = NO;
// All our protocol methods are @optional, so we must check they are actually implemented before calling.
if ([self.delegate respondsToSelector:@selector(loginViewControllerShouldAllowAnonymousLogin:)]) {
// self is passed as the LoginViewController argument to the delegate methods
// in this way our delegate can serve as the delegate of multiple login view controllers, if needed
anonymousLoginAllowed = [self.delegate loginViewControllerShouldAllowAnonymousLogin:self];
}
self.anonSigninButton.hidden = !anonymousLoginAllowed;
}
- (IBAction)loginButtonAction:(UIButton *)sender
{
// We're preteneding our password is always bad. So we assume login succeeds when allowed anonmously
BOOL loginSuccess = [self isAnonymousLoginEnabled];
NSError *loginError = [self isAnonymousLoginEnabled] ? nil : [NSError errorWithDomain:@"domain" code:0 userInfo:nil];
// Fake concurrency
double delayInSeconds = 1.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
// Notify delegate of failure or success
if (loginSuccess) {
if ([self.delegate respondsToSelector:@selector(loginViewControllerDidLoginSuccessfully:)]) {
[self.delegate loginViewControllerDidLoginSuccessfully:self];
}
}
else {
if ([self.delegate respondsToSelector:@selector(loginViewController:didFailWithError:)]) {
[self.delegate loginViewController:self didFailWithError:loginError];
}
}
});
}
- (IBAction)forgotPasswordButtonAction:(id)sender
{
// Notify delegate to handle forgotten password request.
if ([self.delegate respondsToSelector:@selector(loginViewControllerDidReceivePasswordResetRequest:)]) {
[self.delegate loginViewControllerDidReceivePasswordResetRequest:self];
}
}
- (IBAction)signupButtonAction:(id)sender
{
// Notify delegate to handle signup request.
if ([self.delegate respondsToSelector:@selector(loginViewControllerDiDReceiveSignupRequest:)]) {
[self.delegate loginViewControllerDiDReceiveSignupRequest:self];
}
}
- (BOOL)isAnonymousLoginEnabled
{
BOOL anonymousLoginAllowed = NO;
if ([self.delegate respondsToSelector:@selector(loginViewControllerShouldAllowAnonymousLogin:)]) {
anonymousLoginAllowed = [self.delegate loginViewControllerShouldAllowAnonymousLogin:self];
}
return anonymousLoginAllowed;
}
@end
主视图控制器实例化并呈现登录视图控制器，并处理其委托消息:
#import "MainViewController.h"
#import "LoginViewController.h"
#define LOGGED_IN NO
@interface MainViewController () <LoginViewControllerDelegate>
@end
@implementation MainViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Fake loading time to show the modal cleanly
if (!LOGGED_IN) {
double delayInSeconds = 1.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
// Create a login view controller, assign its delegate, and present it
LoginViewController *lvc = [[LoginViewController alloc] init];
lvc.delegate = self;
[self presentViewController:lvc animated:YES completion:^{
NSLog(@"modal completion finished.");
}];
});
}
}
#pragma mark - LoginViewControllerDelegate
- (void)loginViewControllerDidLoginSuccessfully:(LoginViewController *)lvc
{
NSLog(@"Login VC delegate - Login success!");
[self dismissViewControllerAnimated:YES completion:NULL];
}
- (void)loginViewController:(LoginViewController *)lvc didFailWithError:(NSError *)error
{
// Maybe show an alert...
// UIAlertView *alert = ...
}
- (void)loginViewControllerDidReceivePasswordResetRequest:(LoginViewController *)lvc
{
// Take the user to safari to reset password maybe
NSLog(@"Login VC delegate - password reset!");
}
- (void)loginViewControllerDiDReceiveSignupRequest:(LoginViewController *)lvc
{
// Take the user to safari to open signup form maybe
NSLog(@"Login VC delegate - signup requested!");
}
- (BOOL)loginViewControllerShouldAllowAnonymousLogin:(LoginViewController *)lvc
{
return YES;
}
@end
登录在某些方面可能是一个复杂的交互式过程，所以我建议你认真考虑使用委托而不是通知。然而，有一件事可能是有问题的，那就是委托必须只有一个对象。如果您需要多个不同的对象了解登录视图控制器的进度和状态，那么您可能需要使用通知。特别是如果登录过程可以被限制得非常简单，以一种除了传递单向消息和数据之外不需要任何交互的方式，那么通知可以成为一个可行的选择。你可以在通知中传递任意变量回到userInfo属性中，这是你决定在其中填充的任何NSDictionary。通知可能会影响性能，但我知道现在只有当观察者数量达到数百时才会发生这种情况。即使如此，在我看来，它也不是最自然的适合，因为您有父对象(或多或少控制子对象的生命周期)要求第三方对象从子对象更新。
您可以使用协议，这是最好的方法。
我将告诉你如何创建协议的基本思想还有，看看这个问题:如何在Objective-C中创建委托?
下面的代码为您提供了协议的基本概念，在下面的代码中，您可以从MasterViewController到DetailViewController获得按钮标题。
#DetailViewController.h
#import <UIKit/UIKit.h>
@protocol MasterDelegate <NSObject>
-(void) getButtonTitile:(NSString *)btnTitle;
@end
@interface DetailViewController : MasterViewController
@property (nonatomic, assign) id<MasterDelegate> customDelegate;
#DetailViewController.m
if([self.customDelegate respondsToSelector:@selector(getButtonTitile:)])
{
[self.customDelegate getButtonTitile:button.currentTitle];
}
#MasterViewController.m
create obj of DetailViewController
DetailViewController *obj = [[DetailViewController alloc] init];
obj.customDelegate = self;
[self.navigationController pushViewController:reportTypeVC animated:YES];
and add delegate method in MasterViewController.m for get button title.
#pragma mark -
#pragma mark - Custom Delegate Method
-(void) getButtonTitile:(NSString *)btnTitle;
{
NSLog(@"%@", btnTitle);
}