Question

我在我的应用程序中使用MagicalRecord和CoreData Wrapper实现了最喜欢的场景。我正在搜索价值，如果在我的实体中找到该属性，它会将其删除为fav，否则它会将其添加到fav。在这里DX *foundDX = [DX MR_findFirstByAttribute:@"code" withValue:cell.DXCodeName.text]; foundDX是我正在检查的值。
我已经在我的tableView中添加了一个UISearchBar。因此，当加载视图时，它会显示已使用可能不喜欢的fav项目。如果用户搜索并选择一个项目，它会成功将其添加到fav并成功将其从数据模型中删除。但如果我再次点击“收藏”按钮，它就会崩溃。

   if (!foundDX.code) {
        //If we are always getting into here that means that either foundDX is nil
        //or the code is nil so you need to verify the logic around that.
        if (indexPath != nil)
        {
            if (!_AddEditDX) {
                self.AddEditDX = [DX MR_createEntity];
            }
            [self.AddEditDX setCode:cell.DXCodeName.text];
            [self.AddEditDX setDescriptions:cell.DXDescText.text];
            [self.AddEditDX setIsFav:[NSNumber numberWithInt:1]];

            [[NSManagedObjectContext MR_defaultContext] MR_saveToPersistentStoreAndWait];
            [self.favDXArray addObject:self.AddEditDX];
            [self fetchFavDX];

            [cell.DXFavButton setImage:[UIImage imageNamed:@"star_filled"] forState:UIControlStateNormal];
            [KSToastView ks_showToast:@"Added to Favourite" duration:1.0f];

        }
    } else if(self.favDXArray.count > indexPath.row) {
        //You can get rid of the if(foundDX.code) because this is the else block to not having it so we must have it.
        //Only thing to worry about is the array size
        NSLog(@"count is: %ld and row is: %ld",_favDXArray.count, (long)indexPath.row);
        DX *tempDX = [self.favDXArray objectAtIndex:indexPath.row];
        [tempDX MR_deleteEntity];

        [cell.DXFavButton setImage:[UIImage imageNamed:@"star_blank"] forState:UIControlStateNormal];
        [self.favDXArray removeObjectAtIndex:indexPath.row];
        [[NSManagedObjectContext MR_defaultContext] MR_saveToPersistentStoreAndWait];
        [KSToastView ks_showToast:@"Removed from Favourite" duration:1.0f];
    }

通过应用一些断点我发现：
假设代码是E45而foundDX没有第一次找到它并将其添加到数据模型中。然后再按下“收起”按钮将其删除，实际上它已将其删除。但是，如果我再次点击fav按钮，foundDX仍然是E45，因此它会崩溃。但是如果我关闭应用并再次运行它E45就不再存在了。

的更新
我已经更新了上面的代码。我在fetchFavDX中使用viewDidLoad，因此我尝试在上面的代码中更新的方法中调用它。而在fetchFavDX我这样做：

-(void)fetchFavDX {
    self.favDXArray = [NSMutableArray arrayWithArray:[DX MR_findAllSortedBy:@"code" ascending:YES]];
}

现在它在前两次工作正常，这意味着添加/删除/添加/删除。之后它只运行块if (!foundDX.code)，这意味着它不会进入else部分。

Answer 1

你应该检查self.favDXArray计数是否比indexpath.row长，这样就可以实际删除/检索。它会是这样的：

if(self.favDXArray.count > indexPath.row){
    DX *tempDX = [self.favDXArray objectAtIndex:indexPath.row];
    [tempDX MR_deleteEntity];
    [cell.DXFavButton setImage:[UIImage imageNamed:@"star_blank"] forState:UIControlStateNormal];
    [self.favDXArray removeObjectAtIndex:indexPath.row];
    [KSToastView ks_showToast:@"Removed from Favourite" duration:1.0f];
    [[NSManagedObjectContext MR_defaultContext] MR_saveToPersistentStoreAndWait];
}

<强>更新

if (!foundDX.code) {
 //If we are always getting into here that means that either foundDX is nil 
//or the code is nil so you need to verify the logic around that. 
    if (indexPath != nil)
    {
        self.AddEditDX = [DX MR_createEntity];
        [self.AddEditDX setCode:cell.DXCodeName.text];
        [self.AddEditDX setDescriptions:cell.DXDescText.text];
        [self.AddEditDX setIsFav:[NSNumber numberWithInt:1]];

        [[NSManagedObjectContext MR_defaultContext] MR_saveToPersistentStoreAndWait];
        [self.favDXArray addObject:self.AddEditDX];
        [self fetchFavDX];

        [cell.DXFavButton setImage:[UIImage imageNamed:@"star_filled"] forState:UIControlStateNormal];
        [KSToastView ks_showToast:@"Added to Favourite" duration:1.0f];

    }
} else if(self.favDXArray.count > indexPath.row) {
//You can get rid of the if(foundDX.code) because this is the else block to not having it so we must have it. 
//Only thing to worry about is the array size
    NSLog(@"count is: %ld and row is: %ld",_favDXArray.count, (long)indexPath.row);
    DX *tempDX = [self.favDXArray objectAtIndex:indexPath.row];
    [tempDX MR_deleteEntity];

    [cell.DXFavButton setImage:[UIImage imageNamed:@"star_blank"] forState:UIControlStateNormal];
    [self.favDXArray removeObjectAtIndex:indexPath.row];
    [[NSManagedObjectContext MR_defaultContext] MR_saveToPersistentStoreAndWait];
    [KSToastView ks_showToast:@"Removed from Favourite" duration:1.0f];
}

确保获取foundDX的方法正在返回您期望的内容。同时确保添加/删除使您处于预期的状态，即您拥有已添加或删除的内容

MagicalRecord中的findFirstByAttribute再次找到已删除的实体

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