C# – Implementing INotifyPropertyChanged – does a better way exist

.netc++inotifypropertychangedwinforms

Microsoft should have implemented something snappy for INotifyPropertyChanged, like in the automatic properties, just specify {get; set; notify;}
I think it makes a lot of sense to do it. Or are there any complications to do it?

Can we ourselves implement something like 'notify' in our properties. Is there a graceful solution for implementing INotifyPropertyChanged in your class or the only way to do it is by raising the PropertyChanged event in each property.

If not can we write something to auto-generate the piece of code to raise PropertyChanged event?

Best Solution

Without using something like postsharp, the minimal version I use uses something like:

public class Data : INotifyPropertyChanged
{
    // boiler-plate
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }
    protected bool SetField<T>(ref T field, T value, string propertyName)
    {
        if (EqualityComparer<T>.Default.Equals(field, value)) return false;
        field = value;
        OnPropertyChanged(propertyName);
        return true;
    }

    // props
    private string name;
    public string Name
    {
        get { return name; }
        set { SetField(ref name, value, "Name"); }
    }
}

Each property is then just something like:

private string name;
public string Name
{
    get { return name; }
    set { SetField(ref name, value, "Name"); }
}

which isn't huge; it can also be used as a base-class if you want. The bool return from SetField tells you if it was a no-op, in case you want to apply other logic.


or even easier with C# 5:

protected bool SetField<T>(ref T field, T value,
    [CallerMemberName] string propertyName = null)
{...}

which can be called like this:

set { SetField(ref name, value); }

with which the compiler will add the "Name" automatically.


C# 6.0 makes the implementation easier:

protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

...and now with C#7:

protected void OnPropertyChanged(string propertyName)
   => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

protected bool SetField<T>(ref T field, T value,[CallerMemberName] string propertyName =  null)
{
    if (EqualityComparer<T>.Default.Equals(field, value)) return false;
    field = value;
    OnPropertyChanged(propertyName);
    return true;
}

private string name;
public string Name
{
    get => name;
    set => SetField(ref name, value);
}

And, with C# 8 and Nullable reference types, it would look like this:

public event PropertyChangedEventHandler? PropertyChanged;

protected void OnPropertyChanged(string propertyName) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

protected bool SetField<T>(ref T field, T value, [CallerMemberName] string propertyName = "")
{
    if (EqualityComparer<T>.Default.Equals(field, value)) return false;
    field = value;
    OnPropertyChanged(propertyName);
    return true;
}

private string name;
public string Name
{
    get => name;
    set => SetField(ref name, value);
}
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