如何设置一个简单的委托以在两个视图控制器之间进行通信？ [英] How do I set up a simple delegate to communicate between two view controllers?

问题描述

我有两个UITableViewController，需要使用委托将子视图控制器的值传递给父进程。我知道代表是什么，只是想看一个简单的例子。

谢谢

解决方案

简单示例...

我们假设子视图控制器有一个 UISlider 我们希望通过委托将滑块的值传递给父级。

在子视图控制器的头文件中，声明委托类型及其方法： / p>

ChildViewController.h

  #import < UIKit / UIKit.h> 
 
 // 1.向前声明ChildViewControllerDelegate  - 这只是声明
 //存在一个ChildViewControllerDelegate类型，以便我们可以使用它
 //稍后。 
 @protocol ChildViewControllerDelegate; 
 
 // 2.视图控制器类的声明，像往常一样
 @interface ChildViewController：UIViewController 
 
 //委托属性应始终为弱引用
 //参见http://stackoverflow.com/a/4796131/263871的理由
 //（提示：如果您不使用ARC，请使用`assign`而不是`weak`）
 @property（nonatomic，weak）id< ChildViewControllerDelegate>代表; 
 
 //一个简单的IBAction方法，我将与
 // UI中的关闭按钮相关联。我们将在此处理程序中调用委托的childViewController：didChooseValue：
 //方法。 
  - （IBAction）handleCloseButton：（id）sender; 
 
 @end 
 
 // 3.委托人界面的定义
 @protocol ChildViewControllerDelegate< NSObject> 
 
  - （void）childViewController：（ChildViewController *）viewController 
 didChooseValue：（CGFloat）value; 
 
 @end 
  

在子视图控制器的实现中，调用委托方法

ChildViewController.m

  #importChildViewController.h
 
 @implementation ChildViewController 
 
  - （void）handleCloseButton：（id）sender {
 // Xcode会抱怨我们在这里访问一个超过
 //的弱属性，因为理论上可以在访问之间填充
 //导致不可预测的结果。所以我们先从
 //本地，强烈地引用代表开始。 
 id< ChildViewControllerDelegate> strongDelegate = self.delegate; 
 
 //我们的委托方法是可选的，所以我们应该
 //检查代理是否实现它
 if（[strongDelegate responsesToSelector：@selector（childViewController：didChooseValue :)] ）{
 [strongDelegate childViewController：self didChooseValue：self.slider.value]; 
} 
} 
 
 @end 
  

父视图控制器的头文件，声明它实现 ChildViewControllerDelegate 协议。

RootViewController.h

  #import< UIKit / UIKit.h> 
 #importChildViewController.h
 
 @interface RootViewController：UITableViewController< ChildViewControllerDelegate> 
 
 @end 
  

在父视图控制器的实现中，实现委托方法

RootViewController.m

  #importRootViewController.h
 
 @implementation RootViewController 
 
  - （void）tableView：（UITableView *）tableView didSelectRowAtIndexPath：（NSIndexPath *）indexPath {
 ChildViewController * detailViewController = [[ChildViewController alloc] init]; 
 //将self指定为子视图控件的委托
 detailViewController.delegate = self; 
 [self.navigationController pushViewController：detailViewController animated：YES]; 
} 
 
 //实现ChildViewControllerDelegate的委托方法
  - （void）childViewController：（ChildViewController *）viewController didChooseValue：（CGFloat）value {
 
 //做一些有价值的东西... 
 
 // ...然后关闭子视图控制器
 [self.navigationController popViewControllerAnimated：YES]; 
} 
 
 @end 
  

希望这有帮助！ p>

I have two UITableViewControllers and need to pass the value from the child view controller to the parent using a delegate. I know what delegates are and just wanted to see a simple to follow example.

Thank You

解决方案

Simple example...

Let's say the child view controller has a UISlider and we want to pass the value of the slider back to the parent via a delegate.

In the child view controller's header file, declare the delegate type and its methods:

ChildViewController.h

#import <UIKit/UIKit.h>

// 1. Forward declaration of ChildViewControllerDelegate - this just declares
// that a ChildViewControllerDelegate type exists so that we can use it
// later.
@protocol ChildViewControllerDelegate;

// 2. Declaration of the view controller class, as usual
@interface ChildViewController : UIViewController

// Delegate properties should always be weak references
// See http://stackoverflow.com/a/4796131/263871 for the rationale
// (Tip: If you're not using ARC, use `assign` instead of `weak`)
@property (nonatomic, weak) id<ChildViewControllerDelegate> delegate;

// A simple IBAction method that I'll associate with a close button in
// the UI. We'll call the delegate's childViewController:didChooseValue: 
// method inside this handler.
- (IBAction)handleCloseButton:(id)sender;

@end

// 3. Definition of the delegate's interface
@protocol ChildViewControllerDelegate <NSObject>

- (void)childViewController:(ChildViewController*)viewController 
             didChooseValue:(CGFloat)value;

@end

In the child view controller's implementation, call the delegate methods as required.

ChildViewController.m

#import "ChildViewController.h"

@implementation ChildViewController

- (void)handleCloseButton:(id)sender {
    // Xcode will complain if we access a weak property more than 
    // once here, since it could in theory be nilled between accesses
    // leading to unpredictable results. So we'll start by taking
    // a local, strong reference to the delegate.
    id<ChildViewControllerDelegate> strongDelegate = self.delegate;

    // Our delegate method is optional, so we should 
    // check that the delegate implements it
    if ([strongDelegate respondsToSelector:@selector(childViewController:didChooseValue:)]) {
        [strongDelegate childViewController:self didChooseValue:self.slider.value];
    }
}

@end

In the parent view controller's header file, declare that it implements the ChildViewControllerDelegate protocol.

RootViewController.h

#import <UIKit/UIKit.h>
#import "ChildViewController.h"

@interface RootViewController : UITableViewController <ChildViewControllerDelegate>

@end

In the parent view controller's implementation, implement the delegate methods appropriately.

RootViewController.m

#import "RootViewController.h"

@implementation RootViewController

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    ChildViewController *detailViewController = [[ChildViewController alloc] init];
    // Assign self as the delegate for the child view controller
    detailViewController.delegate = self;
    [self.navigationController pushViewController:detailViewController animated:YES];
}

// Implement the delegate methods for ChildViewControllerDelegate
- (void)childViewController:(ChildViewController *)viewController didChooseValue:(CGFloat)value {

    // Do something with value...

    // ...then dismiss the child view controller
    [self.navigationController popViewControllerAnimated:YES];
}

@end

Hope this helps!

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