The Mode property page provides more information about binding modes and an example of how to specify the direction of a binding.
Before going into the different features of data binding outlined above, we will first discuss in the next section the fundamental concepts that are critical to understanding WPF data binding.
Regardless of what element you are binding and the nature of your data source, each binding always follows the model illustrated by the following figure: As illustrated by the above figure, data binding is essentially the bridge between your binding target and your binding source.
The Update Source Trigger property of the binding determines what triggers the update of the source.
The dots of the right arrows in the following figure illustrate the role of the Update Source Trigger property: If the Update Source Trigger value is Property Changed, then the value pointed to by the right arrow of Two Way or the One Way To Source bindings gets updated as soon as the target property changes.
As mentioned previously and as indicated by the arrow in the figure above, the data flow of a binding can go from the binding target to the binding source (for example, the source value changes when a user edits the value of a Text Box) and/or from the binding source to the binding target (for example, your Text Box content gets updated with changes in the binding source) if the binding source provides the proper notifications.
You may want your application to enable users to change the data and propagate it back to the source object.
As described in the last section, the direction of the data flow is determined by the value of the Mode property of the binding.
However, does your source value get updated while you are editing the text or after you finish editing the text and point your mouse away from the Text Box?
The following figure illustrates the different types of data flow: Note that to detect source changes (applicable to One Way and Two Way bindings), the source must implement a suitable property change notification mechanism such as INotify Property Changed.