执行代表团 [英] Implementing delegation

问题描述

我认为我正在关注代表团的工作原理，这里是我遵循的教程，但我在某个地方搞砸了。我期望我的委托给NSLog，但不是。谁能找出我失踪或做错了？

I think I'm following how delegation works, here's the tutorial I followed, but I'm messing up somewhere. I'm expecting my delegate to NSLog but it's not. Can anyone find out what am I missing or doing wrong?

我的 MainViewController.h ：

@interface MainViewController : UITableViewController < AddClassDelegate >

MainViewController.m ：

- (void)cancelAddingClass {
    NSLog(@"Canceled Yo");
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

/*
 When a row is selected, the segue creates the detail view controller as the destination.
 Set the detail view controller's detail item to the item associated with the selected row.
 */
if ([[segue identifier] isEqualToString:@"addClassSegue"]) {

    UINavigationController *nc = (UINavigationController *)segue.destinationViewController;
    AddClassViewController *addClassVC = (AddClassViewController *)[nc.viewControllers objectAtIndex:0];
    addClassVC.delegate = self;
}

我的模态视图控制器 AddClassViewController.h ：

@protocol AddClassDelegate <NSObject>
- (void)cancelAddingClass;
@end

@interface AddClassViewController : UITableViewController

@property (weak, nonatomic) id< AddClassDelegate > delegate;

- (IBAction)cancelButtonPressed:(id)sender;

AddClassViewController.m ：

@synthesize delegate;

- (IBAction)cancelButtonPressed:(id)sender {
    [self.delegate cancelAddingClass];
}

cancelButtonPressed: 

被连接到模态

推荐答案

你的代码看起来不错，这表明问题是我们看不到的地方。我的猜测在这里：

Your code looks fine, which suggests the problem is somewhere we can't see. My guess is here:

AddClassViewController *addClassVC = [segue destinationViewController];
addClassVC.delegate = self;
NSLog(@"segued");

您是否在导航控制器中嵌入了模态视图控制器？如果是这样，destinationViewController会给你导航控制器，而不是AddClassViewController。检查调试器中实际上是什么类的addClassVC。

Have you embedded your modal view controller in a navigation controller? If so, destinationViewController gives you the navigation controller, not the AddClassViewController. Check what class addClassVC actually is in the debugger.

如果是导航控制器，没问题，只需要使用 .viewController 财产。在几行中使它更容易理解：

If it is a navigation controller, no problem, you just need to get to your actual VC using the .viewControllers property. On several lines to make it simpler to understand:

UINavigationController *nc = (UINavigationController *)segue.destinationViewController;
AddClassViewController *addClassVC = (AddClassViewController *)[nc.viewControllers objectAtIndex:0];
addClassVC.delegate = self;

你可以用更少的行来做，但它是一个混乱的铸造和嵌套的括号，这是更难调试

You can do it in fewer lines but it's a mess of casting and nested brackets, which is harder to debug.

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