WPF call method when property changes

Question

In C#, how can a method be called when a property changes (both method and property belong to the same class)?

e.g.,

class BrowserViewModel
{
    #region Properties

    public List<TreeViewModel> Status { get; private set; }
    public string Conditions { get; private set; }

    #endregion // Properties

    // i'd like to call this method when Status gets updated
    void updateConditions
    {
         /* Conditions = something depending on the TreeViewItem select status */
    }
}

Binding

<TreeView Grid.Row="1"
    x:Name="StatusTree"
    ItemContainerStyle="{StaticResource TreeViewItemStyle}"
    ItemsSource="{Binding Path=Status, Mode=OneTime}"
    ItemTemplate="{StaticResource CheckBoxItemTemplate}"
/>

Use-Case (if you are curious)

The property Status is bound to a TreeView control in the xaml. When it is updated, I'd like to call a method that updates the property Conditions. This property is bound to a TextBox in the xaml.

I'm new to Eventing in C#, so am a little lost.

Edit

1. class TreeViewModel implements INotifyPropertyChanged.
2. Conditions is updated by getting the IsChecked Value from the TreeView.
3. The size of the Status List never changes. When a TreeViewItem is selected/unselected the TreeViewModel changes.
4. TreeViewModel source (FooViewModel on this page)
5. Binding code above.

6. Didn't have to change Binding Mode for IsChecked.

       <HierarchicalDataTemplate 
           x:Key="CheckBoxItemTemplate"
           ItemsSource="{Binding Children, Mode=OneTime}"
           >
               <StackPanel Orientation="Horizontal">
               <!-- These elements are bound to a TreeViewModel object. -->
               <CheckBox
                   Focusable="False" 
                   IsChecked="{Binding IsChecked}" 
                   VerticalAlignment="Center"
                   />
               <ContentPresenter 
                   Content="{Binding Name, Mode=OneTime}" 
                   Margin="2,0"
                   />
               </StackPanel>
       </HierarchicalDataTemplate>
   

Answer 1

I assume you want updateConditions to fire whenever an item is added/removed/changed in your list, not if the list reference itself changes.

Since you're implementing INotifyPropertyChanged within your TreeViewModel, I think you'll want to use ObservableCollection<T> instead of a plain List<T>. Check it here: http://msdn.microsoft.com/en-us/library/ms668604.aspx

Represents a dynamic data collection that provides notifications when items get added, removed, or when the whole list is refreshed.

class BrowserViewModel
{
    #region Properties

    public ObservableCollection<TreeViewModel> Status { get; private set; }
    public string Conditions { get; private set; }

    #endregion // Properties

    // i'd like to call this method when Status gets updated
    void updateConditions
    {
         /* Conditions = something */
    }

    public BrowserViewModel()
    {
        Status = new ObservableCollection<TreeViewModel>();
        Status.CollectionChanged += (e, v) => updateConditions();
    }
}

CollectionChanged will fire whenever an item is added/removed/changed. As far as I know, it will consider it "changed" when its reference changes or any of its properties are changed (which is notified through INotifyPropertyChanged)

Just checked it here: http://msdn.microsoft.com/en-us/library/ms653375.aspx

ObservableCollection.CollectionChanged Event Occurs when an item is added, removed, changed, moved, or the entire list is refreshed.

ObservableCollection<T> resides in the System.Collections.ObjectModel namespace, in System.dll assembly.