Figure 2. How to bind a property to a user-level setting.

The great thing of this technique is that you don't need to write a single line of code. In fact, you just need to define one or more settings in the Settings page of the My Project designer (Visual Basic) or Properties designer (C#), for example the MainFormLocation and MainFormSize settings (see Figure 1). It is crucial that these settings are defined as user settings, because application-level settings are read-only. Next, you can select the form, switch to the Properties window, open the (Application Settings) section, click on the arrow near the ClientSize and Location properties, and select the user setting you want to bind the property to. If you haven't created the user setting yet, you can do it now by clicking on the New element. (See Figure 2.)

As I already noted, the noteworthy detail is that these settings are automatically updated when the end user moves or resizes the form. You can bind other properties, for example Text, BackColor, etc. If you perform this action for all the forms in the application, you can implement a simple yet powerful persistance mechanism for all user's preferences, again without writing code!

Obviously, you can extend this mechanism to properties of individual controls. Not all properties can notify to the world that they have been modified, though. More precisely, the control that exposes the property must implement the IBindableComponent interface and must expose an event named XxxxChanged for each property, or it must implement the INotifyPropertyChanged interface (new in .NET 2.0). Most Windows Forms controls, but not all of them, implement these interfaces. For example, the ToolStripItem control doesn't implement it. In this case, the property is assigned correctly when the form loads, but you must update the corresponding user setting via code.