Global Property Changed object casting results in null (in C#)

Question

I am having some trouble with initializing a new variable as the object being sent by the global property changed. I have two classes BeltConfiguration and BeltProperty (both classes have INotifyPropertyChanged ). I have a globalpropertychanged method in the BeltConfiguration class as seen here.

        private void BeltProperty_GlobalPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            BeltProperty validBelt = sender as BeltProperty;
            if (validBelt != null)
            {
                this.Validation = validBelt.Validation;
            }
            switch (e.PropertyName)
            {
                case "Value":
                    this.Validation.ValidState = ConfigurationValid.Unknown;
                    OnPropertyChanged("Validate");
                    break;
                case "ConfigurationInvalid":
                    this.Validation.ValidState = ConfigurationValid.False;
                    OnPropertyChanged("Validate");
                    break;
            }
        }

In the BeltProperty class, I call this with OnGlobalPropertyChanged("ConfigurationInvalid"); However, when I call it, no matter what I do, validBelt always results in being null . I looked at the object sender by stepping through the code and it says that the declaring method, GenericParametersAttributes , and GenericParametersPosition threw an exception of System.InvalidOperationException . I don't know if that has anything to do with why validBelt won't accept sender as BeltProperty . Thanks for any help or advice you can give me.

This is where I called BeltProperty_GlobalPropertyChanged in the Belt Property class.

    private ConfigurationValidation _Validation = new ConfigurationValidation(ConfigurationValid.Unknown, "", "", null);
    /// <summary>
    /// Stores information as to wether this belt property is valid or invalid, and the details.
    /// </summary>
    internal ConfigurationValidation Validation
    {
        get { return _Validation; }
        set {

            _Validation = value;
            if(_Validation.ValidState == ConfigurationValid.False)
            {
                OnGlobalPropertyChanged("ConfigurationInvalid");
            }
        }
    }

    /// <summary>
    /// A global on property change that runs for any instantiated object of this type.
    /// </summary>
    /// <param name="name"></param>
    static void OnGlobalPropertyChanged(string name)
    {
        GlobalPropertyChanged(
            typeof(BeltProperty),
            new PropertyChangedEventArgs(name));
    }

Answer 1

Since you are using a safe cast here:

BeltProperty validBelt = sender as BeltProperty

When validBelt is null after this assignment it means sender cannot be cast to an instance of BeltProperty .

Looking at your calling code it looks like you are not passing an instance of BeltProperty into your event handler.

Assuming GlobalPropertyChanged is your PropertyChangedEventHandler delegate change your OnGlobalPropertyChanged code to this:

/// <summary>
/// A global on property change that runs for any instantiated object of this type.
/// </summary>
/// <param name="name"></param>
static void OnGlobalPropertyChanged(string name)
{
    GlobalPropertyChanged(
        this,
        new PropertyChangedEventArgs(name)
    );
}