Communication between ViewModel and Composer

This page is under construction, so we cannot guarantee the accuracy of the content!

In order to understand the following paragraphs, you had better understand concept of global command and how to bind an event to it.

The global command binding usage section demonstrates how to communicate between multiple ViewModels. We can also use the same mechanism to perform communication between a composer and a ViewModel, but usage is a little different.

Posting a Command from a Composer to a ViewModel

We have already known that global command is triggered by binder sending events into event queue. Hence ViewModels can communicate each other by their own binders. But a composer doesn't have a binder to send a global command for it. Therefore, we provide a utility class, BindUtils, that can do this job. You can use it in a composer.

For example, after adding a product, you want to tell ShoppingCartViewModel to refresh shopping cart's items.

Send a global command in a composer (Sender)

public class MyComposer extends SelectorComposer{

	@Listen("onAddProductOrder=#PrdoDiv #prodGrid row productOrder")
	public void addProduct(Event fe) {

		//business logic of adding a product

		BindUtils.postGlobalCommand(null, null, "updateShoppingCart", null);
	}
}

• we use BindUtils.postGlobalCommand(String queueName, String queueScope, String cmdName, Map<java.lang.String,java.lang.Object> args) to post a command. We leave first two arguments as "null" to use default queue name and default scope (desktop). The third arguments is global command's name. You can send extra data with a Map by the fourth argument.

• The specified global command is then executed by all ViewModel's binders that have subscribed to the event queue in the same (desktop) scope.

In the ShoppingCartViewModel, we should declare a global command method named "updateShoppingCart" to receive this command request and refresh cart items. The code snippet below shows this.

Global command in a ViewModel (Receiver)

public class ShoppingCartViewModel {
	
	...
	
	@GlobalCommand
	@NotifyChange("cartItems")
	public void updateShoppingCart() {
		//update shopping cart
	}
}

Version History

Version	Date	Content
6.0.0	May 2012	Supplement to advanced topic.