[errai-dev] Declarative API for PropertyChangeHandlers in DataBinding

[Mike Brock]

This gets us a little closer to something like this:

@Singleton
public class MyBean {
	@Inject @AutoBound MyModel model;
	@Inject @Bound Label name;

	public void onMyModelChange(@NewModel MyModel updatedModel) {
  		// do something with updatedModel
	}

	@ModelSetter
	public void setModel(MyModel model) {
		this.model = model;
	}
}

Note that I didn't inject a DataBinder<T> but rather the MyModel directly. Also pay attention to the @ModelSetter annotation. The theory behind this is the DataBinder<T> would be created in the Bootstrapper but never actually injected. The @ModelSetter is a hint to create decorator code that proxies that method so the hidden DataBinder's setModel() method can be called, and then the proxied model object then passed on to the MyBean.setModel(). This requires AOP-style parodying of the MyBean in this case. But I think it's a powerful tradeoff.

Mike.

On 2013-03-11, at 8:33 PM, Mike Brock <cbrock at redhat.com> wrote:

> While I was playing tonight I had a few ideas I wanted to bounce off everyone. What about a higher level API for handling change events?
> 
> Consider the following:
> 
> ====HelloWorld.java=========================================
> 
> @EntryPoint
> @Templated("#root")
> public class HelloWorld extends Composite {
>  @Inject @AutoBound private DataBinder<MyModel> model;
> 
>  @Inject @NeedsData @Bound @DataField private TextBox name;
>  @Inject @DataField private Button button;
> 
>  @EventHandler("button")
>  private void onClick(ClickEvent e) {
>    messageBox.setText("Hello there, " + model.getModel().getName());
>  }
> 
>   @OnModelChange
>   public void onMyModelChange(@OldModel     MyModel model,
>                                                             @NewModel   MyModel newModel,
> 							     @Property   String propertyName,
>                                                             @Source     Object source) {
>       // react to change
>   } 
> }
> 
> ----------------------------------------------------------------------------------------------------
> 
> ====ChangeEvents.java======================================
> 
> @Singleton
> public class ChangeEvents [
>   @OnGlobalModelChange
>   public void onMyModelChange(@OldModel     MyModel model,
>                                                             @NewModel   MyModel newModel,
> 							     @Property   String propertyName,
>                                                             @Source     Object source) {
>       // react to change
>   } 
> }
> 
> ----------------------------------------------------------------------------------------------------
> 
> Note: the idea is that each of the specified attributes are optional with the exception you must specify *at least* @OldModel or @NewModel. So in practice you might just do something like this:
> 
> public void onMyModelChange(@NewModel MyModel updatedModel) {
>   // do something with updatedModel
> }
> 
> The general idea is that the @ OnGlobalModelChange would match all *managed* (read: injected automatically by the container such as @AutoBound) DataBinders that match MyModel. Where-as the @OnModelChange in the HelloWorld class would be scoped just to that one ErraiUI bean. 
> 
> ----
> 
> This is just something I brainstormed in about 15 minutes. I am not fixed on this particular approach. But I found myself wanting a declarative way of listening for changes tonight that didn't involve me adding a @PostConstruct and manually adding a PropertyChangeHandler to the DataBinder. 
> 
> 
> 
> 
> 
> 
> 
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