Data Synchronization

The ViewModel and the View each hold their own copy of the data shown on the View. Moreover, the ViewModel often also needs to duplicate at least some of the data provided by the Model. Data therefore needs to be synchronized between these entities. The following sections detail the responsibilities of the developer and suggest supporting classes.

Note
The developer responsibilities below should be read as suggestions rather than rules. For complex scenarios, it probably makes sense to implement things as suggested. In simple cases shortcuts can be taken, for example: For a GUI that only displays data that never changes, it makes little sense to implement change propagation. It is sufficient to implement initialization. For data that is only ever displayed and changed from a single view, change propagation from Model to ViewModel to View is unnecessary and does not need to be implemented.

Note

The developer responsibilities below should be read as suggestions rather than rules. For complex scenarios, it probably makes sense to implement things as suggested. In simple cases shortcuts can be taken, for example:

For a GUI that only displays data that never changes, it makes little sense to implement change propagation. It is sufficient to implement initialization.
For data that is only ever displayed and changed from a single view, change propagation from Model to ViewModel to View is unnecessary and does not need to be implemented.

This topic contains the following sections:

Initialization
Change Propagation from View to ViewModel to Model
Change Propagation from Model to ViewModel to View

Initialization

Entity	Developer Responsibilities	Supporting Classes
Model	Implement property getters
ViewModel	Call property getters in Model Implement property getters	OneWayBinding TwoWayBinding MultiBinding
View	Set DataContext Use binding expressions in XAML

Change Propagation from View to ViewModel to Model

Entity	Developer Responsibilities	Supporting Classes
Model	Implement property setters
ViewModel	Implement property setters Call property setters in Model	OneWayBinding TwoWayBinding MultiBinding
View	Set DataContext Use binding expressions in XAML

Change Propagation from Model to ViewModel to View

Entity	Developer Responsibilities	Supporting Classes
Model	Implement INotifyPropertyChanged	NotifyPropertyChanged
ViewModel	Implement INotifyPropertyChanged Subscribe to PropertyChanged events of the Model	NotifyPropertyChanged OneWayBinding TwoWayBinding MultiBinding
View	Set DataContext Use binding expressions in XAML