Patterns and Practices series has an article titled Prism ( Composite Application Guidance for WPF)
This helps to build WPF client applications that are flexible and composite. Composite applications are loosely coupled, the parts independently evolve but work together in the overall application.
Prism can help you develop your WPF client application.
Typically Prism is intended for complex UI applications. As such it should be evaluated for use in your application. You can determine the fit if you want the following:
You are building an application that integrates and renders data from multiple sources
You are developing, testing and deploying modules independent of the rest of the application.
Your application has several views and will add more over time.
Your application targets both WPF and Silverlight and you want to share code between the two.
You shouldn't use Prism if your application doesn't require any of the above.
Using Prism is non-invasive because you can integrate existing libraries with the Prism library through a design that favors composition over the inheritance. You can incrementally add Prism capabilities to your application and you can opt-in and opt-out of these capabilties.
Prism commands are a way to handle User Interface actions. WPF allows the presenter or controller to handle the UI logic separately from the UI layout and presentation. Presenter or controller can handle command while they live outside the logical tree. WPF-routed commands deliver command messages through the UI elements in the tree, but the elements outside the tree will not receive these messages because they only propagate events up or down the from the focused element to the explicitly stated element. Additionally WPF-routed commands required a command handler in the code behind.
DelegateCommand and CompositeCommand are two custom implementations of the ICommand interface that require that deliver messages outside of the logical tree. These DelegateCommand uses its delegate to invoke the CanExecute or Execute method on the target object when the command is invoked. Because the class is generic, it invokes compile time checking of the command parameters which traditional WPF commands don't. It removes the need for creating a new command type for every instance where you need commanding
CompositeCommand has multiple child commands. Action on the composite command is invoked against all its children. When you click a submit all button, all the associated submit commands are invoked. When the Execute and CanExecute method is invoked, it calls the respective methods on the child control. Additionally, the ShouldExecute method is provided if one or more of the child commands are to be unsubscribed from the calls. The command can unsubscribe by setting the IsActive property to false. Individual commands are registered and unregistered using the RegisterCommand and UnregisterCommand
SilverLight supports the data binding only against the DataContext or against static resources. Silverlight does not support the data binding against other elements in a visual tree. This causes issues if you want to bind to a control that is within an Items control. In such cases, a solution is to bind the command property to a static resource and set the value of the static resource to the command you want to bind.
The command support in Silverlight is built using an attached behaviour pattern. This pattern connects events raised by controls to code on a presenter or a presentation model. It comprises of two parts an attached property and a behaviour object. The attached property establishes a relationship between the target control and the behaviour object. The behaviour object monitors the target control and takes actions based on event or state change on the control.
This helps to build WPF client applications that are flexible and composite. Composite applications are loosely coupled, the parts independently evolve but work together in the overall application.
Prism can help you develop your WPF client application.
Typically Prism is intended for complex UI applications. As such it should be evaluated for use in your application. You can determine the fit if you want the following:
You are building an application that integrates and renders data from multiple sources
You are developing, testing and deploying modules independent of the rest of the application.
Your application has several views and will add more over time.
Your application targets both WPF and Silverlight and you want to share code between the two.
You shouldn't use Prism if your application doesn't require any of the above.
Using Prism is non-invasive because you can integrate existing libraries with the Prism library through a design that favors composition over the inheritance. You can incrementally add Prism capabilities to your application and you can opt-in and opt-out of these capabilties.
Prism commands are a way to handle User Interface actions. WPF allows the presenter or controller to handle the UI logic separately from the UI layout and presentation. Presenter or controller can handle command while they live outside the logical tree. WPF-routed commands deliver command messages through the UI elements in the tree, but the elements outside the tree will not receive these messages because they only propagate events up or down the from the focused element to the explicitly stated element. Additionally WPF-routed commands required a command handler in the code behind.
DelegateCommand and CompositeCommand are two custom implementations of the ICommand interface that require that deliver messages outside of the logical tree. These DelegateCommand uses its delegate to invoke the CanExecute or Execute method on the target object when the command is invoked. Because the class is generic, it invokes compile time checking of the command parameters which traditional WPF commands don't. It removes the need for creating a new command type for every instance where you need commanding
CompositeCommand has multiple child commands. Action on the composite command is invoked against all its children. When you click a submit all button, all the associated submit commands are invoked. When the Execute and CanExecute method is invoked, it calls the respective methods on the child control. Additionally, the ShouldExecute method is provided if one or more of the child commands are to be unsubscribed from the calls. The command can unsubscribe by setting the IsActive property to false. Individual commands are registered and unregistered using the RegisterCommand and UnregisterCommand
SilverLight supports the data binding only against the DataContext or against static resources. Silverlight does not support the data binding against other elements in a visual tree. This causes issues if you want to bind to a control that is within an Items control. In such cases, a solution is to bind the command property to a static resource and set the value of the static resource to the command you want to bind.
The command support in Silverlight is built using an attached behaviour pattern. This pattern connects events raised by controls to code on a presenter or a presentation model. It comprises of two parts an attached property and a behaviour object. The attached property establishes a relationship between the target control and the behaviour object. The behaviour object monitors the target control and takes actions based on event or state change on the control.
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