OnPropertyChanged does not compile

Question

I am trying to binding the content of a label in xaml to a public variable in C# behind. When never the value gets set from the UI, it should trigger the value in the C#.

This VS2008 C# + WPF

However, it does not compile, and it says:

error CS1502: The best overloaded method match for

'System.Windows.DependencyObject.OnPropertyChanged(System.Windows.DependencyPropertyChangedEventArgs)' has some invalid arguments

error CS1503: Argument '1': cannot convert from 'string' to 'System.Windows.DependencyPropertyChangedEventArgs'

Here is some code

C# code

 private bool _isLogOn;

        public  bool IjmFinished
        {
            get 
            {
               // return _fl.ProcessFinished;

                return _isLogOn;
            }
            set 
            {
                _isLogOn = value;
               OnPropertyChanged("IjmFinished");
            }
        }

xaml

 <Label Margin="120,0,0,82" Height="30" VerticalAlignment="Bottom" Content="{Binding Path = IjmFinished, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged, Converter={StaticResource IjmFinishedStatusConverter}}"  HorizontalAlignment="Left" Width="80" />  

If I uncomment out OnPropertyChanged("IjmFinished"); it can compile. I am wondering where I did wrong, and how I should change it? Thanks.

Answer 1

It looks like you're calling a method in your class that is meant to handle a Dependency Property change. Instead, you need to raise the INotifyPropertyChanged.PropertyChanged event:

PropertyChanged(this, new PropertyChangedEventArgs("ImFinished"));

---

Note that typically you will write a helper method for this in your base view-model class, which looks something like this:

protected void RaisePropertyChanged(string propertyName)
{
    var evt = PropertyChanged;   // create local copy in case the reference is replaced
    if (evt != null)             // check if there are any subscribers
        evt (this, new PropertyChangedEventArgs(propertyName));
}

That way you can use simply RaisePropertyChanged("ImFinished").

---

One final note: C# version 5 has a new attribute CallerMemberName which allows the RaisePropertyChanged method to get the calling property's name:

protected void RaisePropertyChanged([CallerMemberName]string propertyName = null)
{
    var evt = PropertyChanged;   // create local copy in case the reference is replaced
    if (evt != null)             // check if there are any subscribers
        evt (this, new PropertyChangedEventArgs(propertyName));
}

This saves you from the use of magic strings to specify the property name -- just call RaisePropertyChanged() from the property setter.