Communication between ViewModel and Composer

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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
	}
}

Posting a Command from a ViewModel to a Composer

Because a ViewModel has a binder attached to it, triggering a global command doesn't need BindUtils. We just can use global command binding.

Assume that we want to inform a composer to update shopping cart's items.

Bind global command in a ZUL (Sender)

 <window apply="org.zkoss.bind.BindComposer" binder="@init(queueName='myqueue')"
   viewModel="@id('vm') @init('example.MyViewModel')" >

    <button id="addProduct" label="Add" onClick="@global-command('updateShoppingCart')"/>
</window>

As we mentioned before, global command is sent by event queue, the composer (receiver) should subscribe to the same scope event queue to receive this global command.

Subscribe to the event queue for the global command (Receiver)

public class MyComposesr extends SelectorComposer<Component>{
	
	@Subscribe("myqueue")
	public void updateShoppingCart(Event evt){
		if(evt instanceof GlobalCommandEvent){
			if("updateShoppingCart".equals(((GlobalCommandEvent)evt).getCommand())){
				//update shopping cart's items
			}				
		}
	}
}

• For @Subscribe , please refer to ZK Developer's Reference/MVC/Controller/Subscribe to EventQueues.
• To subscribe a event queue by method call, please refer to ZK Developer's Reference/Event Handling/Event Queues#Subscribe_to_an_Event_Queue

Version History

Version	Date	Content
6.0.0	May 2012	Supplement to advanced topic.