为什么会崩溃？
CategoryOfExpense *newCatEx = (CategoryOfExpense *) [NSEntityDescription entityForName:kCategoryOfExpense inManagedObjectContext:moc];
newCatEx.name = self.nameTextField.text; <- crashes here
newCatEx.icon = [NSData dataWithData:UIImagePNGRepresentation(self.iconImageView.image)];
错误是：
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Can't modify an immutable model.'
您正在调用entityForName:inManagedObjectContext:which 返回一个NSEntityDescription. 这将是实体的定义，就像您在构建模型时在 GUI 中描述它的方式一样。
我相信你想要的是insertNewObjectForEntityForName:inManagedObjectContext:创建一个新NSManagedObject的实体。
你这样做是错的。这是来自开发网站：
编辑实体描述：
Entity descriptions are editable until they are used by an object graph manager.
This allows you to create or modify them dynamically.
However, once a description is used (when the managed object model to which it belongs
is associated with a persistent store coordinator), it must not (indeed cannot) be changed.
This is enforced at runtime: any attempt to mutate a model or any of its sub-objects
after the model is associated with a persistent store coordinator causes an exception to
be thrown. If you need to modify a model that is in use, create a copy, modify the copy,
and then discard the objects with the old model.
最后提到的例外就是你得到的。进一步接近最后是你需要做的。
试试这个：
您可以通过调用实例来获取模型
-mutableCopy的可变副本。NSManagedObjectModel