How to force notifying DataContext changed?

[liwuqingxin]

Hello everyone!

EDIT 1 --------

More broadly, the question is how to force to notify an AvaloniaProperty changed, even it is not changed actually.
For an instance that implemented INotifyPropertyChanged, we can use instance.PropertyChanged(...) to do that. But with AvaloniaObject's AvaloniaProperty, how to do that?

END EDIT 1 --------

I have a custom DataGrid control. I use static expression like 'value / sum(value)' to calculate some column's value. In that situation, the calculation only performs when the DataContext of the row, which is also the cells'DataContext, is changed or the control is creating.

Now when I update a rowdata.value from '10' to '20', I want to force to notify that the DataRow's DataContext is changed, to update the expression column's cell. How can I do that efficiently?

I try to set the DataContext of the DataRow to null first and then set it back immediately. It works, but is not efficient enough. The DataContext updated twice in that way.

So, I would like to find out an api that is like INotifyPropertyChanged.PropertyChanged, which can notify the AvaloniaProperty change even if it is not changed actually.

Many thanks!

[timunie]

that's a task for your ItemViewModel. this.RaisePropertyChanged(nameof(TheOtherProperty)) if you use ReactiveUI. If you use another MVVM toolkit, lookup their docs.

[timunie]

this.RaisePropertyChanged(string.Empty) --> That should trigger the Binding for all properties

[liwuqingxin]

DataContextProperty is AvaloniaProperty but DirectProperty. RaisePropertyChanged does not fit for that. And I have tried to call the overload method of RaisePropertyChanged by reflecting. But it does not take effect.

 internal void RaisePropertyChanged<T>(
            AvaloniaProperty<T> property,
            Optional<T> oldValue,
            BindingValue<T> newValue,
            BindingPriority priority,
            bool isEffectiveValue);

[timunie]

On your ViewModel, leave the control alone. It's not how MVVM works

[liwuqingxin]

I have no ViewModel... I am creating a TableControl like DataGrid In Avalonia. So in my custom table control, I don't care about the ViewModel that the user provided. I Just wants to get notifed when any property of the row data changed and then notify the expression column to perform it's calculation again.

[liwuqingxin]

The StaticExpressionColumn binds to the DataContext and use a converter to calculate expression. So only the DataContext is changed the expression can be calculated again.

public class StaticExpressionColumn : DoubleBasedExpressionColumn
{
    protected override Control OnCreateCellControl()
    {
        var control = new LightTextBlock();
        var binding = new Binding
        {
            Priority = BindingPriority.LocalValue,
            Converter = new DynamicCvt((value, type, parameter, culture) =>
            {
                var ret = value == null ? value : CalcRawValue(value);
                return $"{ret:f2}";
            }),
        };
        control.Bind(TextBlock.TextProperty, binding);
        
        return control;
    }

    protected override string? GetFallbackHeader()
    {
        return Expression;
    }
}