iphone - 关闭模态视图 Controller 并将数据传回

Question

我有两个 View Controller ，firstViewController 和 secondViewController。我正在使用此代码切换到我的 secondViewController(我还向它传递了一个字符串):

secondViewController *second = [[secondViewController alloc] initWithNibName:nil bundle:nil];

second.myString = @"This text is passed from firstViewController!";

second.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;

[self presentModalViewController:second animated:YES];

[second release];

然后我在 secondViewController 中使用这段代码切换回 firstViewController:

[self dismissModalViewControllerAnimated:YES];

一切正常。我的问题是，如何将数据传递给 firstViewController？我想将另一个字符串从 secondViewController 传递到 firstViewController。

Answer 1

您需要使用委托(delegate)协议(protocol)...以下是操作方法:

在您的 secondViewController 的头文件中声明一个协议(protocol)。它应该看起来像这样:

#import <UIKit/UIKit.h>

@protocol SecondDelegate <NSObject>
-(void)secondViewControllerDismissed:(NSString *)stringForFirst
@end


@interface SecondViewController : UIViewController
{
    id myDelegate;  
}

@property (nonatomic, assign) id<SecondDelegate>    myDelegate;

不要忘记在您的实现 (SecondViewController.m) 文件中合成 myDelegate:

@synthesize myDelegate;

在您的 FirstViewController 的头文件中订阅 SecondDelegate 协议(protocol):

#import "SecondViewController.h"

@interface FirstViewController:UIViewController <SecondDelegate>

现在，当您在 FirstViewController 中实例化 SecondViewController 时，您应该执行以下操作:

// If you're using a view controller built with Interface Builder.
SecondViewController *second = [[SecondViewController alloc] initWithNibName:"SecondViewController" bundle:[NSBundle mainBundle]];
// If you're using a view controller built programmatically.
SecondViewController *second = [SecondViewController new]; // Convenience initializer that uses alloc] init]
second.myString = @"This text is passed from firstViewController!";
second.myDelegate = self;
second.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentModalViewController:second animated:YES];
[second release];

最后，在您的第一个 View Controller (FirstViewController.m) 的实现文件中，为 secondViewControllerDismissed 实现 SecondDelegate 的方法:

- (void)secondViewControllerDismissed:(NSString *)stringForFirst
{
    NSString *thisIsTheDesiredString = stringForFirst; //And there you have it.....
}

现在，当您要关闭第二个 View Controller 时，您想要调用第一个 View Controller 中实现的方法。这部分很简单。你所要做的就是，在你的第二个 View Controller 中，在关闭代码之前添加一些代码:

if([self.myDelegate respondsToSelector:@selector(secondViewControllerDismissed:)])
{
    [self.myDelegate secondViewControllerDismissed:@"THIS IS THE STRING TO SEND!!!"];
}
[self dismissModalViewControllerAnimated:YES];

委托(delegate)协议(protocol)非常、非常、非常有用。熟悉它们对你有好处:)

NSNotifications 是实现此目的的另一种方式，但作为最佳实践，当我想跨多个 viewController 或对象进行通信时，我更喜欢使用它。如果您对使用 NSNotifications 感到好奇，这是我之前发布的答案:Firing events accross multiple viewcontrollers from a thread in the appdelegate

编辑:

如果要传递多个参数，dismiss 之前的代码如下所示:

if([self.myDelegate respondsToSelector:@selector(secondViewControllerDismissed:argument2:argument3:)])
{
    [self.myDelegate secondViewControllerDismissed:@"THIS IS THE STRING TO SEND!!!" argument2:someObject argument3:anotherObject];
}
[self dismissModalViewControllerAnimated:YES];

这意味着您的 SecondDelegate 方法在您的 firstViewController 中的实现现在看起来像:

- (void) secondViewControllerDismissed:(NSString*)stringForFirst argument2:(NSObject*)inObject1 argument3:(NSObject*)inObject2
{
    NSString thisIsTheDesiredString = stringForFirst;
    NSObject desiredObject1 = inObject1;
    //....and so on
}