通过 NSNotification 从 UICollectionView 中删除单元格 [英] Deleting cells from UICollectionView via NSNotification

问题描述

为了简单起见，我有一个基于 UICollectionView 的简单应用程序 - 一个 UICollectionView 和一个基于 NSMutableArray 的数据模型.

I have a simple UICollectionView based app - one UICollectionView and a NSMutableArray based data model for simplicity.

我可以通过 didSelectItemAtIndexPath: 委托方法毫无问题地删除单元格:

I can delete cells with no problem via the didSelectItemAtIndexPath: delegate method:

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{
    [self.data removeObjectAtIndex:[indexPath row]];
    [self.collectionView deleteItemsAtIndexPaths:@[indexPath]];
}

但是，我正在尝试通过 UICollectionViewCell 子类中的 UIMenuController 添加删除选项，该子类通过 UILongPressGestureRecognizer 触发工作正常，我成功触发 NSNotification

However, I'm trying to add a delete option via a UIMenuController in a UICollectionViewCell subclass which is triggered via a UILongPressGestureRecognizer which all works fine and I successfully trigger an NSNotification

-(void)delete:(id)sender{
      NSLog(@"Sending deleteme message");
      [[NSNotificationCenter defaultCenter] postNotificationName:@"DeleteMe!" object:self userInfo:nil];
}

我在 ViewController 中捕获它并调用以下方法:

I catch it in my ViewController and call the following method:

-(void)deleteCell:(NSNotification*)note{
       MyCollectionViewCell *cell = [note object];
       NSIndexPath *path = nil;
       if((path = [self.collectionView indexPathForCell:cell]) != nil){
           [self.data removeObjectAtIndex:[path row]];
           [self.collectionView deleteItemsAtIndexPaths:@[path]];
       }
}

它在 deleteItemsAtIndexPaths 上崩溃:调用

And it crashes on the deleteItemsAtIndexPaths: call

-[UICollectionViewUpdateItem action]: unrecognized selector sent to instance 0xee7eb10

我已经检查了所有明显的东西——比如来自 NSNotification 的对象和从 indexPathForCell: 调用创建的 indexPath，这一切看起来都很好.似乎我在两个地方都使用相同的信息调用 deleteItemsAtIndexPath:，但由于某种原因，它在通过通知路由时失败了.

I've checked everything obvious - like the object from NSNotification and the indexPath created from the indexPathForCell: call and it all seems totally fine. It seems like I'm calling deleteItemsAtIndexPath: with the same information in both places, but for some reason it fails when it goes via the notification route.

这是错误中给出的地址的信息:

This is the info at the address given in the error:

(lldb) po 0xee7eb10
(int) $1 = 250080016 <UICollectionViewUpdateItem: 0xee7eb10> index path before update (<NSIndexPath 0x9283a20> 2 indexes [0, 0]) index path after update ((null)) action (delete)

也许更新为空后的索引路径很重要……

Perhaps the index path after update being null is significant...

有什么想法吗?

推荐答案

我找到了一个粗略但可行的解决方法，它甚至会检查是否已经在未来的版本中实现了操作(比类别更好)

I found a crude but working workaround, and it even checks if action is already implemented in a future release (better than a category)

// Fixes the missing action method when the keyboard is visible
#import <objc/runtime.h>
#import <objc/message.h>
__attribute__((constructor)) static void PSPDFFixCollectionViewUpdateItemWhenKeyboardIsDisplayed(void) {
    @autoreleasepool {
    if ([UICollectionViewUpdateItem class] == nil) return; // pre-iOS6.
    if (![UICollectionViewUpdateItem instancesRespondToSelector:@selector(action)]) {
            IMP updateIMP = imp_implementationWithBlock(^(id _self) {});
            Method method = class_getInstanceMethod([UICollectionViewUpdateItem class], @selector(action));
            const char *encoding = method_getTypeEncoding(method);
            if (!class_addMethod([UICollectionViewUpdateItem class], @selector(action), updateIMP, encoding)) {
                NSLog(@"Failed to add action: workaround");
            }
        }
    }
}

添加了对 iOS5 的检查.
Edit2:我们在许多商业项目中都提供了它(http://pspdfkit.com)，而且效果很好.

Added check for iOS5.
We're shipping that in lots of commercial projects (http://pspdfkit.com) and it works great.

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