NotifyPropertyChangedBase

NotifyPropertyChangedBase provides a simple to use yet powerful base class NotifyPropertyChanged that implements the INotifyPropertyChanged interface. Whether you're writing UWP, Xamarin, WPF or any other app, it will help you work with data.

This is an open-source project so feel free to send a pull request or open an issue.

Pre-release

If you want to get updates more frequently or test bugfixes and new features before they go into production and you don't mind the possibility of new bugs, you can use the pre-release version of NotifyPropertyChangedBase from MyGet.org.

Get it here

How to use it?

NotifyPropertyChangedBase library helps you use INotifyPropertyChanged interface without needing to write your own logic. The one and only thing you need to do is to make your models inherit from the abstract class NotifyPropertyChanged. So instead of worrying about backing stores - variables that hold data of properties - about compairing data or calling the PropertyChanged event you will register your property and this class will do the rest.

It's usage is very similar to the usage of DependencyObject, that you may be familiar with from UWP or WPF, however it does not inherit from it nor it can only be used on the UI thread. You can access it from any thread you want.

To benefit from the advantages of NotifyPropertyChangedBase, you have to register your property using the RegisterProperty method. It has three required parameters and one overload accepting fourth parameter:

• name of the property (using it you'll be accessing its value and doing all the work with the property)
• type of the property
• default value of the property
• (optional) property changed callback - a method that will be invoked after given property changes, but before the PropertyChanged event is invoked, providing you info about the previous value of the property and it's new - current value

Please note that unlike DependencyProperty.Register the RegisterProperty method here does not return anything and you don't have to store anything. You're accessing the property using only it's name.

To get and set values of registered properties you'll use GetValue and SetValue or ForceSetValue. The difference between SetValue and ForceSetValue is that the latter always sets the new value to a property and invokes the PropertyChanged event and registered callbacks, no matter whether the value is different from the current one. However SetValue checks whether the old value and the new one are differet using the Equals method (you may want to override it to achieve the desired result on this check). SetValue assigns the new value and invokes the PropertyChanged event and registered callbacks only if the two values are not equal.

All these methods have an argument propertyName specifying which property are you working with but you can fully omit these as the compiler will pass the name of property/method from which these methods are called from because the argument has the CallerMemberNameAttribute (does not apply to .NET 4.0 where the attribute is not available). SetValue and ForceSetValue have one another argument that is passed before the propertyName containing the value to be set to given property.

There's also the OnPropertyChanged method, also having a propertyName argument with the same attribute, which you can use to invoke the PropertyChanged event manually.

PropertyChangedCallback

Besides the PropertyChanged event that is invoked when any of the properties changes, NotifyPropertyChangedBase provides the PropertyChangedCallback that is registered for each property independently. Registered callbacks are invoked always before the PropertyChanged event.

There are two ways to register them - using overloaded RegisterProperty method which accepts a delegate of type PropertyChangedCallback as the last argument or using RegisterPropertyChangedCallback. The latter is designed to add another callback any time after registering the property. You can also unregister a callback, registered using whichever of those two methods, using the UnregisterPropertyChangedCallback method.

The handlers of these callbacks get two values as arguments - sender which holds the reference to the class that invoked that certain callback and e of type PropertyChangedCallbackArgs which has the following properties:

• Handled - indicates whether this certain callback has been handled. Default value is false.
• OldValue - holds the previous value of the related property.
• NewValue - holds the current value of the related property.

Having a control over everything

Using the IsPropertyChangedEventInvokingEnabled and IsPropertyChangedCallbackInvokingEnabled properties you can enable/disable invocation of the PropertyChanged event or registered callbacks. Their default value is true but setting them to false will disable the respected events so even the ForceSetValue method will not be invoking them.

Setting IsPropertyChangedCallbackInvokingEnabled to false will not unregister already registered callbacks.

Example

Here's a simple class using some advantages of NotifyPropertyChangedBase. It has two properties, Bar and Greeting. Both are backed by NotifyPropertyChanged class so anytime their value is changed, the PropertyChanged event is automatically invoked.

    using NotifyPropertyChangedBase;

    class Foo : NotifyPropertyChanged
    {
        public int Bar
        {
            get { return (int)GetValue(); }
            set { SetValue(value); }

            // These will do the same:
            // get { return (int)GetValue(nameof(Bar)); }
            // get { return (int)GetValue("Bar"); }
        }
        public string Greeting
        {
            get { return (string)GetValue(); }
            set { SetValue(value); }
        }

        public Foo()
        {
            // Property without a callback
            RegisterProperty(nameof(Bar), typeof(int), 0);
            // This will do the same:
            // RegisterProperty("Bar", typeof(int), 0);

            // Property with a callback
            RegisterProperty(nameof(Greeting), typeof(string), null, GreetingPropertyChanged);
        }

        private void GreetingPropertyChanged(NotifyPropertyChanged sender, PropertyChangedCallbackArgs e)
        {
            Console.WriteLine($"Value of Greeting changed from '{e.OldValue}' to '{e.NewValue}'");
        }
    }

I'm using the nameof keyword but you can of course use just a string i.e. "Bar" etc. when working with properties.

This is just a simple example. Of course you can call GetValue, SetValue and ForceSetValue anywhere in the code, not only in the body of related properties but using Bar = 5; over SetValue(5, nameof(Bar)); and so on seems much simpler to me.

Structure of the NotifyPropertyChanged class

All the members of this class (except of the PropertyChanged event) are protected so only derived classes can use them.