NonPublicAccess.md

Non Public Access Extension Points

Someta allows you to provide non-public access to methods in a target class. This can be useful, for example, if you have a NotifyPropertyChanged extension point with a protected OnPropertyChanged method, you can use this extension point to provide acccess to that protected method from within your extension point.

Note: Currently this extension point only supports methods. (i.e. not properties, events, etc.)

INonPublicAccess

This interface works in conjunction with InjectAccess and InjectTarget. The purpose of this interface is to act as a marker for whether or not to look for properties decorated with the attribute InjectAccess in your extension point. If such properties are found, the corresponding properties will be set to a delegate that matches the signature of the target method plus an addition parameter in the front representing the instance.

The target method is matched to the InjectAccess property by adding the InjectTarget attribute to the target method. The Key property should be the same for both.

Example

public void NonPublicAccess()
{
    var testClass = new NonPublicAccessTestClass();
    int counter = 0;
    testClass.PropertyChanged += (sender, args) => counter++;
    testClass.Value = 42;
    Console.WriteLine(counter);         // Prints 1
}

[NotifyPropertyChanged]
class NonPublicAccessTestClass : INotifyPropertyChanged
{
    // Except for this property, the rest of this class would be suitable as a base class for any class that wants to reuse this logic.
    public int Value { get; set; }

    public event PropertyChangedEventHandler? PropertyChanged;

    [InjectTarget(nameof(OnPropertyChanged))]
    protected virtual void OnPropertyChanged(string propertyName, object oldValue, object newValue)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    // this is only here to cause an overload situation
    protected virtual void OnPropertyChanged(string propertyName, object oldValue, string newValue)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

[AttributeUsage(AttributeTargets.Class)]
class NotifyPropertyChanged : Attribute, IPropertySetInterceptor, INonPublicAccess
{
    [InjectAccess("OnPropertyChanged")]
    public Action<object, string, object, object>? OnPropertyChanged { get; set; }

    public void SetPropertyValue(PropertyInfo propertyInfo, object instance, object oldValue, object newValue, Action<object> setter)
    {
        if (!Equals(oldValue, newValue))
        {
            setter(newValue);
            OnPropertyChanged?.Invoke(instance, propertyInfo.Name, oldValue, newValue);
        }
    }
}

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