How to Safely Implement INotifyPropertyChanged for Property Value Change Notifications?

How to Notify Property Value Changes Using Events

To observe property value changes, you can utilize the INotifyPropertyChanged interface, which includes the PropertyChanged event. This event can be subscribed to by consumers to detect alterations in specific properties.

public interface INotifyPropertyChanged
{
    event PropertyChangedEventHandler PropertyChanged;
}

Safe Implementation of INotifyPropertyChanged with Events

While Richard's earlier response introduced an unsafe implementation, here's a revised version that ensures thread safety:

public class MyClass : INotifyPropertyChanged
{
    private string imageFullPath;

    protected void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
            handler(this, e);
    }

    protected void OnPropertyChanged(string propertyName)
    {
        OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
    }

    public string ImageFullPath
    {
        get { return imageFullPath; }
        set
        {
            if (value != imageFullPath)
            {
                imageFullPath = value;
                OnPropertyChanged("ImageFullPath");
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

This implementation:

• Centralizes the property-change notification method for easy application to multiple properties.
• Avoids race conditions by making a copy of the PropertyChanged delegate.
• Conforms fully to the INotifyPropertyChanged interface.

Additional Specific Property Change Event

For additional granularity, you can define a separate event for a specific property, such as:

protected void OnImageFullPathChanged(EventArgs e)
{
    EventHandler handler = ImageFullPathChanged;
    if (handler != null)
        handler(this, e);
}

public event EventHandler ImageFullPathChanged;

In the property's setter, invoke both the general OnPropertyChanged event and the specific OnImageFullPathChanged event.

Simplifying Property Name Acquisition (C# 4.5 Only)

Finally, for C# 4.5 and above, utilize the CallerMemberAttribute to automatically extract the property name, eliminating the need for manual string literals:

protected void OnPropertyChanged(
        [System.Runtime.CompilerServices.CallerMemberName] string propertyName = "")
    {
        OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
    }

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