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

问题描述

我有一个简单的基于UICollectionView的应用程序 - 一个UICollectionView和一个基于NSMutableArray的数据模型，为了简单起见。

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

我可以通过didSelectItemAtIndexPath：delegate方法删除没有问题的单元格：

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<$ c添加删除选项$ c> UIMenuController 在 UICollectionViewCell 子类中，它是通过 UILongPressGestureRecognizer 触发的很好，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：call创建的indexPath，这一切看起来都很好。看起来我正在调用deleteItemsAtIndexPath：在两个地方使用相同的信息，但由于某种原因，当它通过通知路由时它会失败。

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.

这是信息在错误中给出的地址：

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)

更新后的索引路径可能很重要...

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

任何想法？

推荐答案

我找到了一个粗略但有效的解决方法，它甚至会检查行动是否已在未来版本中实施（优于某个类别）

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");
            }
        }
    }
}

编辑：添加了对iOS5的检查。

编辑2：我们在很多商业项目中发布了这些内容（ http：// pspdfkit.com ）它很棒。

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

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