无法获得自定义@protocol在iOS上工作 [英] Can't get custom @protocol working on iOS

问题描述

注意：以下是使用启用了自动引用计数（ARC）的iOS。我认为ARC可能有很多与为什么它不工作，因为这是根据我通过谷歌找到的例子设置。

我试图创建一个协议，通知用户从UITableView中选择的文件名。

FileListViewController.h

  @protocol FileListDelegate< NSObject> 
  - （void）didSelectFileName：（NSString *）fileName; 
 
 @end 
 
 @interface FileListViewController：UITableViewController 
 {
 @private 
 NSArray * fileList; 
 id< FileListDelegate>代表; 
} 
 @property（nonatomic，retain）NSArray * fileList; 
 @property（nonatomic，assign）id< FileListDelegate>代表; 
 
 @end 
  

FileListViewController.m

  #importFileListViewController.h
 
 @implementation FileListViewController 
 
 @synthesize fileList; 
 @synthesize delegate; 
  

这会导致

错误。

  @synthesize delegate; 
 

这是FileListViewController.m：错误：自动引用计数问题：现有的ivar'委托' unsafe_unretained属性'delegate'必须是__unsafe_unretained

如果我改变FileListViewController.h把__weak和（weak），那么它会运行。

  @protocol FileListDelegate< NSObject> 
  - （void）didSelectFileName：（NSString *）fileName; 
 
 @end 
 
 @interface FileListViewController：UITableViewController 
 {
 @private 
 NSArray * fileList; 
 __weak id< FileListDelegate>代表; 
} 
 @property（nonatomic，retain）NSArray * fileList; 
 @property（weak）id< FileListDelegate>代表; 
 
 @end 
  

但是当我尝试设置代理时，应用崩溃。一个称为ImportViewController的视图是从'FileListViewController'创建一个视图，并将委托设置为它自己（ImportViewController），所以我可以实现我的自定义协议'didSelectFileName'。我得到的错误是

* 由于未捕获异常NSInvalidArgumentException终止应用程序，原因：' - [ImportViewController setDelegate：]：unrecognized选择器发送到实例0x6c7d430'

我运行的代码是

ImportViewController.m

   - （void）tableView：（UITableView *）tableView didSelectRowAtIndexPath：（NSIndexPath *）indexPath 
 {
 FileListViewController * fileListViewController = [self.storyboard instantiateViewControllerWithIdentifier：@filelist]; 
 
 [fileListViewController setDelegate：self]; 
 [self.navigationController pushViewController：fileListViewController animated：YES]; 
 
} 
  

我的问题是：

• 为什么放置（weak）和__weak使它工作？我不
  明白为什么这个工作，因为我发现它googling和没有一个
  的解释。


• 为什么无法使用
  '[fileListViewController setDelegate：self];'设置我的委托？似乎
  编译器不知道委托存在。

解决方案

看起来像：

  FileListViewController * fileListViewController = 
 [self.storyboard instantiateViewControllerWithIdentifier：@filelist]; 
  

您没有获得 FileListViewController 对象。看看它说的消息：

- [ImportViewController setDelegate：]：无法识别的选择器发送到实例0x6c7d430 p>

这就是为什么您的应用程式崩溃。还要尝试定义一个retain属性，而不是仅仅分配，如果代理被释放在其他地方，您的应用程序不会崩溃。

Note: the below is using iOS with Automatic Reference Counting (ARC) enabled. I think ARC may have a lot to do with why it isn't working as this is set up as per examples i've found via google.

I am trying to create a protocol to notify a delegate of the filename the user selects from a UITableView.

FileListViewController.h

@protocol FileListDelegate <NSObject>
- (void)didSelectFileName:(NSString *)fileName;

@end

@interface FileListViewController : UITableViewController
{
    @private
        NSArray *fileList;
        id <FileListDelegate> delegate;
}
@property (nonatomic, retain) NSArray *fileList;
@property (nonatomic, assign) id <FileListDelegate> delegate;

@end

FileListViewController.m

#import "FileListViewController.h"

@implementation FileListViewController

@synthesize fileList;
@synthesize delegate;

This gives an error at the

@synthesize delegate;

line which is "FileListViewController.m: error: Automatic Reference Counting Issue: Existing ivar 'delegate' for unsafe_unretained property 'delegate' must be __unsafe_unretained"

If i change FileListViewController.h putting __weak and (weak) then it will run.

@protocol FileListDelegate <NSObject>
- (void)didSelectFileName:(NSString *)fileName;

@end

@interface FileListViewController : UITableViewController
{
    @private
        NSArray *fileList;
        __weak id <FileListDelegate> delegate;
}
@property (nonatomic, retain) NSArray *fileList;
@property (weak) id <FileListDelegate> delegate;

@end

But when I try to set the delegate the app crashes. A view called 'ImportViewController' is creating a view from 'FileListViewController' and setting the delegate to itself (ImportViewController) so I can implement my custom protocol of 'didSelectFileName'. The error I get is;

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ImportViewController setDelegate:]: unrecognized selector sent to instance 0x6c7d430'

The code I am running is;

ImportViewController.m

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    FileListViewController *fileListViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"filelist"];

    [fileListViewController setDelegate:self];
    [self.navigationController pushViewController:fileListViewController animated:YES];

}

My Questions are:

• Why does putting (weak) and __weak in make it work? I don't understand why this works as I found it googling and there wasn't an explanation.
• Why can't I set my delegate using this '[fileListViewController setDelegate:self];' ? It seems like the compiler doesn't know 'delegate' exists.

解决方案

It seems that with :

FileListViewController *fileListViewController =
    [self.storyboard instantiateViewControllerWithIdentifier:@"filelist"];

you didn't get an FileListViewController object. Look at the message it says :

-[ImportViewController setDelegate:]: unrecognized selector sent to instance 0x6c7d430

and that why your app crashes. Also try to define a retain property, instead of just assign, in case the delegate is deallocated elsewhere, your app won't crash.

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