Observable Collection 子项中的数据验证

Question

I want to have a list of properties of different types. Each property (eg BoolProperty , StringProperty ,..) derives from the PropertiesBase class. PropertiesBase class has the member PropertyName .

So there exist an ObservableCollection<PropertiesBase> where a datagrids ItemSource binds to. I am using WPF with MVVMLight.

If the PropertyName of a property is changed, it should be validated if the name is unique in the context of the observable collection.

    private string _propertyName;
    public string PropertyName
    {
        get => _propertyName;
        set
        {
            if (NAME_IS_NOT_UNIQUE)           <---- HOW TO SOLVE THIS
            {
                throw new ArgumentException("Property name must be unique");
            }

            if (_propertyName == value)
                return;
            _propertyName = value;
            RaisePropertyChanged("PropertyName");
        }
    }

My question is now:

How can I check in the PropertiesBase member PropertyName if the name is unique?

As this collection could be loaded from JSON I am not able to hand over a reference to the collection in the child constructors.

Thanks for any help!

Answer 1

It should be clear that a single entity cannot perform any validation based on any values in the other entities since it doesn't know anything about them.

You should either perform the validation in the collection itself or in the class that instantiates the collection and keep a reference to it.

You could for example handle the CollectionChanged event and hook up an event handler to the PropertyChanged event for each PropertiesBase that gets added to the collection. You perform the validation in the error handler. This should be easy since you have access to all items.

When it comes to "mark" and entity as invalid, you could for example do this using an IsValid property or similar. If you implement the INotifyDataErrorInfo interface in your model class, you could for example raise the ErrorsChanged event whenever the IsValid gets set from the event handler.

If you want to perform the validation in the setters of the model properties, you must get a reference to the collection in the model class somehow. There is no way around that.