Distinguish if the user or the program changed a value in a wpf datagrid

Question

i have a mvvm application in which i have a DataGrid in Wpf and want to get notified if a user changes a value in a column.

All dataGridColumns have a binding to my viewmodel, which invokes a PropertyChanged Command if it gets changed. Now the Problem is, how i can determine if the property has been changed by the user or by the code? Because i only want to add a note to the corresponding line when it has been changed manually by the user.

The Column of interest is implemented like this in wpf:

 <DataGridTextColumn
  Header="DIL"
  Binding="{Binding DilutionFactor, StringFormat={}{0:n4}}" 
  Visibility="{Binding Value,
  Source={StaticResource DilVis}, 
  Converter={StaticResource BooleanToVisibilityConverter}}" 
  IsReadOnly="False"/>

Which is bound to the ViewModel Property:

    public double DilutionFactor
    {
        get { return _dilutionFactor; }
        set
        {
            _dilutionFactor = value;
            Update(); // PropertyChanged Command
            UpdatePipetteVolumes(); // function to update corresponding volumes
        }
    }

Is there a event or anything i can use to trigger a method when the user changes the value of the DIL column, which is not triggered when the code updates the value?

Answer 1

You could set a boolean flag each time before you programmatically change the value. Then in the property setter you can check that property to see if the user invoked the change. However, this method might need a lot of code changes for heavily used properties.

Another way: Add a second property which just sets and returns the existing property. Then use that new property for the datagrid binding:

public double DilutionFactorUser
{
    get { return this.DilutionFactor; }
    set
    {
        this.DilutionFactor = value;
        // Here comes the code that is only executed on user-invoked changes
    }
}

public double DilutionFactor
{
    get { return _dilutionFactor; }
    set
    {
        _dilutionFactor = value;
        Update(); // PropertyChanged Command
        UpdatePipetteVolumes(); // function to update corresponding volumes
    }
}

Set up your Datagrid to bind to DilutionFactorUser