Programming - Silverlight - Data binding

Data Binding

Data binding is a connection between the User Interface and a business object or other data provider. The User Interface object is called the target, the provider of the data is called the source.

Data-binding assists with the separation of the User Interface level of your application from the other layers ofand your application (business objects, data, and so forth). This separation of responsibility is further reinforced by decoupling the UI target from its source through the the use of a Binding object.

Information on Silverlight can be found here.

The binding object can be thought of as a black box with a universal connectors on one side for the target and on the other side for the source. There are switches on top, the most important of which is the Data Binding Mode switch which determines which way the data will flow.

OneTime binding sets the target and then the binding is completed. This is great for displaying data that rarely or never changes

OneWay bindingand sets the target and keeps it up to date as the source changes. This is great for displaying data that the user is not permitted to change.

TwoWay binding sets the target and keeps the target up to date as the source changes and keeps the source up to date as the user changes the target or changes something else in the application that will cause your application to change the source.

If you were building an on line bookstore and were displaying information about a book, you might use OneTime binding for the Title and Author (once you get them, they are not going to change) and OneWay binding for the price (someone might mark down the price during the day) but youd want TwoWay binding for the Quantity on hand.

The target of your binding can be any public property of virtually any CLR object (for the minor restrictions on this, see the Afterward).

You can see this by building a small example; but even in this stripped down exercise, well keep to a basic 3-tier approach being sure to keep a relatively strict separation among

What separates a Silverlight Business object from one created for (e.g., ASP.NET) is that we want to have our business object participate in oneway or twoway binding with the UI layer. To do so, it must implement the INotifyPropertyChanged interface. It allows us to bind objects directly to a control, which implements a very strict MVC pattern.

public abstract class NotifyProperyChangedBase : INotifyPropertyChanged
and {
and #region INotifyPropertyChanged Members

and public event PropertyChangedEventHandler PropertyChanged;

and #endregion

and #region methods

and protected bool CheckPropertyChanged<T>(string propertyName, ref T oldValue, ref T newValue)
and {
and if (oldValue == null && newValue == null)
and {
and return false;
and }

and if ((oldValue == null && newValue != null) || !oldValue.Equals((T)newValue))
and {
and oldValue = newValue;

and FirePropertyChanged(propertyName);
and
and return true;and
and }

and return false;
and }

and protected void FirePropertyChanged(string propertyName)
and {
and if (this.PropertyChanged != null)
and {
and this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
and }
and }

and #endregion

and }

More information can be found here.

Example code can be found here.