Commands

http://msdn.microsoft.com/en-us/library/ms752308.aspx

• commands separate the semantics and the originator of an action from its logic
• allows the command logic to be customized for different targets
• The command is the action to be executed.
• The command source is the object which invokes the command (e.g. MenuItem, Button, and KeyGesture)
• The command target is the object that the command is being executed on.
• The command binding is the object which maps the command logic to the command.
• The implementation logic is the responsibility of the object on which the command is being executed on
• The command source can explicitly set the command target
• The InvalidateRequerySuggested method forces the CommandManager to raise the RequerySuggested event
• Related Topics - ApplicationCommands, KeyGesture, MouseGesture, KeyBinding

http://www.codeproject.com/KB/WPF/WpfCommandPatternApplied.aspx

To use the command system, the following approach is suggested:

1. Design and implement the command class hierarchy
2. Design and implement the command unit tests
3. Create a CommandCollection: static binding of each command with a CommandDescription
4. Embed button image resources
5. Add Command references in XAML
6. Configure the tooltip format upon application start
7. Setup the CommandRepository at application start: CommandRepository.AddRange()
8. Setup the CommandBinding in the application window: CommandBindings.AddRange(CommandRepository.Bindings )

With this framework the implementation logic is the responsibility of the command being executed -- MSDN states, "implementation logic is the responsibility of the object on which the command is being executed."  Is this a problem?

http://www.devx.com/DevX/Article/37893/0/page/2

Sample with two ListBox.CommandBindings binding to the same command

• WPF commands don't implement command behavior
• WPF commands merely notify UI elements that a command has been invoked
• The UI elements must implement any desired behavior

http://www.devx.com/DevX/Article/37893/0/page/3

Sample custom command (InsertCustomer)

http://www.codeproject.com/KB/WPF/SmartRoutedCommandsInWPF.aspx

• Paradoxically, routed commands are very useful because they don't do anything
• standard execution logic should be used as a fallback plan if the routed command was not handled by any element in the tree
• the RoutedCommand class does not expose any virtual methods that we can override to specify our default execution logic
• Implements SmartRoutedCommand: RoutedCommand w/ IsCommandSync dependency property, Can/ExecuteCore methods.
• This technique is like having the root of the element tree forward our command a notification that it is being used but nobody knows what to do, so that we can then use the subclass's default logic

The dependency property allows for marking a "root" element -- probably a window:

<Window x:Class="SmartRoutedCommandDemo.Window1" ... local:SmartRoutedCommand.IsCommandSink="True" >

In this example the default logic executes if nobody CanExecute the command.

NOTE: The window IsCommandSink for all instances of SmartRoutedCommand.  What if I only want this for specific commands?

Data Binding and Templating

http://msdn.microsoft.com/en-us/library/ms742521.aspx

[Notes]