dismissModalViewController并传回数据

问题描述：

我有两个视图控制器， firstViewController 和 secondViewController 。我使用此代码切换到我的secondViewController（我也传递一个字符串）：

I have two view controllers, firstViewController and secondViewController. I am using this code to switch to my secondViewController (I am also passing a string to it):

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中使用此代码切换回firstViewController：

I then use this code in secondViewController to switch back to the firstViewController:

[self dismissModalViewControllerAnimated:YES];

所有这一切都正常。我的问题是，如何将数据传递给firstViewController？我想从secondViewController传递一个不同的字符串到firstViewController。

All of this works fine. My question is, how would I pass data to the firstViewController? I would like to pass a different string into the firstViewController from the secondViewController.

答

你需要使用委托协议...这里是怎么做：

You need to use delegate protocols... Here's how to do it:

在你的secondViewController的头文件中声明一个协议。它应如下所示：

Declare a protocol in your secondViewController's header file. It should look like this:

#import <UIKit/UIKit.h>

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


@interface SecondViewController : UIViewController
{
    id myDelegate;  
}

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

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

Don't forget to synthesize the myDelegate in your implementation (SecondViewController.m) file:

@synthesize myDelegate;

在FirstViewController的头文件中订阅SecondDelegate协议：

In your FirstViewController's header file subscribe to the SecondDelegate protocol by doing this:

#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：

Now when you instantiate SecondViewController in FirstViewController you should do the following:

// 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，在第一个视图控制器（FirstViewController.m）的实现文件中，实现SecondDelegate的方法secondViewControllerDismissed：

Lastly, in the implementation file for your first view controller (FirstViewController.m) implement the SecondDelegate's method for secondViewControllerDismissed:

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

现在当你'重新关闭要调用第一个视图控制器中实现的方法的第二个视图控制器。这部分很简单。你所要做的就是，在你的第二个视图控制器中，在解雇代码之前添加一些代码：

Now when you're about to dismiss the second view controller you want to invoke the method implemented in the first view controller. This part is simple. All you do is, in your second view controller, add some code before the dismiss code:

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

委托协议非常，非常有用，非常有用。熟悉它们对你有好处：）

Delegate protocols are EXTREMELY, EXTREMELY, EXTREMELY useful. It would do you good to familiarize yourself with them :)

NSNotifications是另一种方法，但作为一种最佳实践，我更喜欢在我想要沟通时使用它跨多个viewControllers或对象。如果您对使用NSNotifications感到好奇，这是我之前发布的答案：从appdelegate中的一个主题中的多个viewcontrollers发送事件

NSNotifications are another way to do this, but as a best practice, I prefer using it when I want to communicate across multiple viewControllers or objects. Here's an answer I posted earlier if you're curious about using NSNotifications: Firing events accross multiple viewcontrollers from a thread in the appdelegate

编辑：

如果你想传递多个参数，解雇之前的代码如下所示：

If you want to pass multiple arguments, the code before dismiss looks like this:

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

这意味着你的firstViewController中的SecondDelegate方法实现现在看起来像：

This means that your SecondDelegate method implementation inside your firstViewController will now look like:

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

dismissModalViewController并传回数据

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