How can I avoid recursion when updating my ViewModel properties?

Question

In my View I have a slider and a combobox.

When I change the slider, I want the combobox to change.

When I change the combobox, I want the slider to change.

I can udpate one or the other, but if I try to update both I get a StackOverflow error since one property keeps updating the other in an infinite loop.

I've tried putting in a Recalculate() where the updating is done in one place, but still run into the recursion problem.

How can I have each control update the other without going into recursion?

in View:

<ComboBox 
    ItemsSource="{Binding Customers}"
    ItemTemplate="{StaticResource CustomerComboBoxTemplate}"
    Margin="20"
    HorizontalAlignment="Left"
    SelectedItem="{Binding SelectedCustomer, Mode=TwoWay}"/>


<Slider Minimum="0" 
        Maximum="{Binding HighestCustomerIndex, Mode=TwoWay}" 
        Value="{Binding SelectedCustomerIndex, Mode=TwoWay}"/>

in ViewModel:

#region ViewModelProperty: SelectedCustomer
private Customer _selectedCustomer;
public Customer SelectedCustomer
{
    get
    {
        return _selectedCustomer;
    }

    set
    {
        _selectedCustomer = value;
        OnPropertyChanged("SelectedCustomer");
        SelectedCustomerIndex = _customers.IndexOf(_selectedCustomer);
    }
}
#endregion

#region ViewModelProperty: SelectedCustomerIndex
private int _selectedCustomerIndex;
public int SelectedCustomerIndex
{
    get
    {
        return _selectedCustomerIndex;
    }

    set
    {
        _selectedCustomerIndex = value;
        OnPropertyChanged("SelectedCustomerIndex");
        SelectedCustomer = _customers[_selectedCustomerIndex];
    }
}
#endregion

Answer 1

try in the set functions something like:

public int SelectedCustomerIndex
{
    get
    {
        return _selectedCustomerIndex;
    }

    set
    {
        if (value != _selectedCustomerIndex)
        {
         _selectedCustomerIndex = value;
         OnPropertyChanged("SelectedCustomerIndex");
         SelectedCustomer = _customers[_selectedCustomerIndex];
        }
    }
}

to fire the events only when there is an actual change in value. This way, a second call to the set property with the same value does not cause another change event.

You have to do that for the other property as well of course.