BB84.Notifications 3.3.616

BB84.Notifications

This repository contains relevant abstractions and implementations for one- and two-way binding of properties, for notifications about changed properties, for notifications about changed collections and for the Relay Command Pattern for synchronous and asynchronous operations.

Usage

Depending on the application, there are several ways to skin a cat.

The notifiable property class and interface

Designed with one or two way binding in mind.

public INotifiableProperty<int> NotifiableInt { get; set; } = new NotifiableProperty<int>(default);

If the property is changed, the PropertyChangingEventHandler is triggered before the value changes and the PropertyChangedEventHandler is triggered after the value has changed.

• The PropertyChangingEventHandler contains via the PropertyChangingEventArgs the name of the property that is changing and when casted to PropertyChangingEventArgs<T> the old value of the property.
• The PropertyChangedEventHandler contains via the PropertyChangedEventArgs the name of the property that has changed and when casted to PropertyChangedEventArgs<T> the new value of the property.

Further implementation possibilities can be achieved with the help of the INotifiableProperty<T> interface.

The notifiable object base class and interface

Designed to handle changes at the class level and propagate them.

public sealed class TestClass : NotifiableObject
{
    private int _property;

    public int Property
    {
        get => _property;
        set => SetProperty(ref _property, value);
    }
}

If the property is changed, the PropertyChangingEventHandler is triggered before the value changes and the PropertyChangedEventHandler is triggered after the value has changed.

• The PropertyChangingEventHandler contains via the PropertyChangingEventArgs the name of the property that is changing and when casted to PropertyChangingEventArgs<T> the old value of the property.
• The PropertyChangedEventHandler contains via the PropertyChangedEventArgs the name of the property that has changed and when casted to PropertyChangedEventArgs<T> the new value of the property.

Further implementation possibilities can be achieved with the help of the INotifiableObject interface.

The notifiable collection base class and interface

The NotifiableCollection class provides methods to handle the change within a collection and propagate it to the outside.

public sealed class MyStringCollection : NotifiableCollection, ICollection<string>
{
  private readonly Collection<string> _collection;

  public MyStringCollection()
    => _collection = new Collection<string>();

  ..
}

Most of the implementation must be done despite the base class itself. The intention has been to be able to signal the state of a collection before (CollectionChangingEventHandler) or after (CollectionChangedEventHandler) the addition, deletion or modification of objects.

• The CollectionChangingEventHandler contains via the CollectionChangingEventArgs the CollectionChangeAction and when casted to CollectionChangingEventArgs<T> the old value of the object.
• The CollectionChangedEventHandler contains via the CollectionChangedEventArgs the CollectionChangeAction and when casted to CollectionChangedEventArgs<T> the new value of the object.

Further implementation possibilities can be achieved with the INotifiableCollection interface or the INotifyCollectionChanged and INotifyCollectionChanging interfaces.

The notification attributes

The NotifyChangedAttribute and the NotifyChangingAttribute propagating the information also to those properties the are defined via the constructor. An example implementation could look like this:

private sealed class TestClass : NotifyPropertyBase
{
  private int _quantity;
  private int _value;

  public TestClass(int quantity, int value)
  {
    Quantity = quantity;
    Value = value;
  }

  [NotifyChanged(nameof(TotalValue))]
  public int Quantity { get => _quantity; set => SetProperty(ref _quantity, value); }

  [NotifyChanged(nameof(TotalValue))]
  public int Value { get => _value; set => SetProperty(ref _value, value); }

  public int TotalValue => Quantity * Value;
}

If the Quantity property or the Value property is changed, a PropertyChanged event is also triggered for the TotalValue property.

Documentation

The complete API documentation can be found here.