A view is a visual representation of concepts within your application. Everything you show in the main application window is contained within a view.

There can be multiple views on an application page, but only one view is active at a time. View instances encapsulate the creation of and access to the visual presentation of the underlying control. A view's descriptor, which is effectively a singleton, can be asked to instantiate new instances of a single view for display within an application with multiple windows. In other words, a single view instance is never shared between windows.

There can be multiple views on an application page, but only one view is active at a time. View instances encapsulate the creation of and access to the visual presentation of the underlying control. A view's descriptor, which is effectively a singleton, can be asked to instantiate new instances of a single view for display within an application with multiple windows. In other words, a single view instance is never shared between windows.

View descriptors produce the page components (in this case views) that will be shown to the users.

Creating a new view is done through subclassing the AbstractView class. This class mandates you to implement one method: createControl. In our example, the initial view class looks like this:

public class InitialView extends AbstractView
{
    // omitted for brevity

	protected JComponent createControl()
        {
		// In this view, we're just going to use standard Swing to place a
		// few controls.

		// The location of the text to display has been set as a Resource in the
		// property descriptionTextPath. So, use that resource to obtain a URL
		// and set that as the page for the text pane.

		JTextPane textPane = new JTextPane();
		JScrollPane spDescription = getComponentFactory().createScrollPane(textPane);
		try {
			textPane.setPage(getDescriptionTextPath().getURL());
		}
		catch (IOException e) {
			throw new RuntimeException("Unable to load description URL", e);
		}

		JLabel lblMessage = getComponentFactory().createLabel(getFirstMessage());
		lblMessage.setBorder(BorderFactory.createEmptyBorder(5, 0, 5, 0));

		JPanel panel = getComponentFactory().createPanel(new BorderLayout());
		panel.add(spDescription);
		panel.add(lblMessage, BorderLayout.SOUTH);

		return panel;
	}
}

To show a view on screen, you need to create a view descriptor. Creating a descriptor is easy based on the view. Every view can gas a view descriptor, creating it if needed.

            
view.getDescriptor();
        

Setting the current view is done by using a ShowViewCommand. This command sets the view of the application window in which the command is located.

To create such a command, use the following definition:

new ShowViewCommand("myId", myView.getDescriptor());

You can now use this command in your menu, or create a button in another view to switch to the defined view.

In the previous chapter, we explained how we can make shared commands, whose behavior is dependent on the context.

When creating a view, these shared commands’ behavior can be changed to add context-specific behavior (such as a ‘New’ or ‘Delete’ action). This is done by registering a command executor to the shared command’s id. The view class supports this registration by overriding a method

            
context.register("newContactCommand", newContactExecutor);
        

This executor then handles the behavior of the command

            
private class NewContactExecutor implements ActionCommandExecutor
{
    public void execute() {
        // put logic here
    }
}