NSComboBoxBindings

I’ve been trying to get this work for several days now and it becomes an headache for me…

I’ve created a NSArrayController that is responsible for a set of NSManagedObjects. One of the related entity property is a ‘category’ relationship. Another CategoryArrayController is then associated to that entity.

What I want to do is to manage Categories through a NSComboBox box. I’ve set bindings to :

content : CategoryArrayController.arrangedObjects

contentValues : CategoryArrayController.arrangedObjects.category

value : TransactionArrayController.selection.category

That works fine for programmatically added category value, that is I can select them through the NSComboBox. However, I cannot add a new category in the user interface. When I enter it, I get a message :

2005-11-28 11:44:10.198 test[426] ** -[NSCFString _isKindOfEntity:] selector not recognized [self = 0x3f7b90]*

Does anyone have a idea for that ?

Well, I assume that “category” is a to-one relationship to a “category” entity. contentValues (note the pluralization) should be pointing to a set (a to-many relationship) like “categories” … further, it should be pointed to a string value (because contentValues is alist of the strings that will be displayed to the user) … So it should be arrangedObjects.categories.categoryTitle or something similar.

… oops - let me amend my statement after looking more closely. Your CategoryArrayController controls your “categories” … so, assuming your category entity has a “categoryTitle” or similar string property, contentValues should be bound to arrangedObjects.categoryTitle. Sorry for any confusion caused by my quick answer.

I finally managed to do it. Here is the final mail I posted to the cocoa mailing list

So I’ve got the following model (credits to Wain ;) :

< Transaction > < category > «————> < Category > < category >

The NSCombobox ‘ bindings should be set to

    content : CategoryArrayController.arrangedObjects
    contentValues : CategoryArrayController.arrangedObjects.category
    value : TransactionArrayController.selection.category.category

Indeed, value expects a NSString, to be printed in the text area of the NSCombobox.

Now, Coredata cannot automatically update the ‘category’ Relationship in the Transaction Entity, as the value in not a NSManagedObject.

So we must intercept the NSCombox Selection change, and code it ourselves. I did it with comboBoxSelectionDidChange: delegate method :

(void)comboBoxSelectionDidChange:(NSNotification *)notification {
// User entered a known category name

         NSEnumerator *e = categoryController arrangedObjects] objectEnumerator];
         id categoryObject;

          while ( (categoryObject = [e nextObject]) ) {                               
              if ([[categoryObject valueForKey:@"category"] isEqualToString:[categoryComboBox objectValueOfSelectedItem)
              {
                  unsigned int selectionIndex = [transactionArrayController selectionIndex];            

                  NSManagedObject *transaction =  transactionArrayController arrangedObjects] objectAtIndex:selectionIndex];
                  [transaction setValue:categoryObject forKey:@"category"];

                  break;
               }
           } }

Ok, what about adding new category ? I had a little problem, because :

nor controlTextDidEndEditing: neither textDidEndEditing: [[NSComboBox delegate method were called, for a currently unknown reason
an “An error occurred” message modal window appeared, because a category name was expected…

I had to do something “very early”, so I use the NSComboBox contr:isValidObject: delegate method (from NSControl).

(BOOL)control:(NSControl *)control isValidObject:(id)object { BOOL categoryIsOK = FALSE; NSManagedObject *category; NSString *categoryName = [NSString stringWithString:object]; [categoryName retain];

// User entered a known category name NSEnumerator *e = categoryController arrangedObjects] objectEnumerator]; id categoryObject;

while ( (categoryObject = [e nextObject]) ) { if ([[categoryObject valueForKey:@”category”] isEqualToString:categoryName]) { categoryIsOK = TRUE; category = categoryObject; break; } }

// Existing category not found, User is creating a new category if (categoryIsOK == FALSE) { [[NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
```
  category = [NSEntityDescription
      insertNewObjectForEntityForName:@"Category" inManagedObjectContext:managedObjectContext];
   
  [category setValue:categoryName forKey:@"category"];
  [categoryController addObject:category];
  categoryIsOK = TRUE;   }
```
unsigned int selectionIndex = [transactionArrayController selectionIndex];

NSManagedObject *transaction = [[transactionArrayController arrangedObjects] objectAtIndex:selectionIndex];

[transaction setValue:category forKey:@”category”];

return TRUE; }

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