Difference between revisions of "JFace Data Binding/SSE"

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===== Beans =====
 
===== Beans =====
 
[["[DataBinding] Best pratice to observe instance model (Bean, EMF..) which change"
 
http://www.eclipse.org/newsportal/article.php?id=80276&group=eclipse.platform#80276]
 
  
 
==== IObserving/ILazyObserving ====
 
==== IObserving/ILazyObserving ====

Revision as of 09:08, 16 March 2009

Contents

Target

Project Structured Source Editing (SSE) which is sub-project of WTP provides the capability to manage structured document (like DOM XML, CSS document..).

Target of JFace Data Binding/SSE is to support bindings with SSE nodes (DOM, CSS...). Today sources of this project are not available because we are discussing with Eclipse Team to see where we can put this project. This project can be used for instance when you wish manage XML content with an UI editor like :

  • PDE which manage plugin.xml with an UI (Extensions page).
  • JSF Web Tools which manage faces-config.xml with an UI.


Into JFace Data Binding/SSE sample you can find a Shapes Editor which manage XML content. Here you can see that SWT Text title UI is bounded with title attribute of diagram element :

ShapesDOMSSEEditor.png

JFace DOM-SSE Databinding

Before explaining features of JFace DOM-SSE Databinding, if you don't know DOM-SSE, I adwice you to read the section #What is DOM-SSE?

Features/Node instances observed

To explain JFace DOM-SSE Databinding features, take the sample Shapes DOM-SSE Editor, which bind attribute title of root element of the DOM Document with SWT Text title. The observed Node is root element :

Element diagram = document.getDocumentElement();

This node change each time, as soon as user change content of XML editor (remove the diagram element, recreate it...).

We start with the XML content

   <diagram title="My shapes diagram"

You can see, that XML is not well formatted because diagram element is not closed. WST is enable to built W3c DOM Document even if XML content is not well formatted.

Bind with existing observed Node

When you open the XML shape file into Shapes DOM-SSE Editor, you can see XML editor is filled with XML content and SWT Text UI has "My shapes diagram" value :

Jface-db-sse-shapes-editor 1.png

In this case, diagram element instance is observed.

Observed Node = instance1.

Bind with null observed Node

Remove the XML content of the XML editor, the XML editor is blank and SWT Text UI has blank value :

Jface-db-sse-shapes-editor 2.png

In this case, root element is null and it's this null value wich is observed.

Observed Node = instance2.

Re-bind observed Node

Re-type the XML content into XML editor :

   <diagram title="My shapes diagram"

Diagram element is created and append it to the DOM. SWT Text UI has again "My shapes diagram" value.

Observed Node = instance3.

Lazy observed Node

Imagine you have blank XML content into XML editor and that user type "M", into SWT Text title. With standard databinding, XML editor will not updated because observed Node doesn't exist. With JFace DOM-SSE Databinding you can manage that. It's called Lazy Observed Node.

To test that, set blank XML content into XML editor. this action remove diagram element instance3. Observed Node is null (Observed Node = instance4).

Type "M" into SWT Text title. This action generate diagram element and rebind it (Observed Node =instance5). This re-binding generate title attribute with "M" value :

Jface-db-sse-shapes-editor 3.png

Sample code

Before read below code, you must understand #Concept of JFace DOM-SSE Databinding. This sampel show you how bind SWT Text title with title attribute of diagram element :


Realm realm = ...
DataBindingContext context = ...

// 1. Create container observed instance for DOM-SSE 
IInstanceObservedContainer container = new
  DOMModelInstanceObservedContainer(model, this);
		
// 2. Create diagram observed with lazy mode.
IObserving diagramObserving =  new ILazyObserving() {
  public Object getObserved() {
    return document.getDocumentElement();
  }

  public Object createObserved() {
    Element diagram = document.createElement("diagram");
    return document.appendChild(diagram);
  }
};
		
// 3. Create IObservableValue with InstanceObservables. 
// InstanceObservables#observeValue create an ObservedValue by using 
// diagramObserving and register it into the instance container
IObservableValue diagramObservable = InstanceObservables.observeValue(container, diagramObserving);
 
// Bind SWT Text 1 with title attribute of root Node.
context.bindValue(
       SWTObservables.observeText(titleText, SWT.Modify),  
       SSEDOMObservables.observeDetailAttrValue(realm,diagramObservable, "title"), 
       null, null);

Concept

As you can see into the #Features/Node instances observed section, JFace DOM-SSE Databinding manage :

  • Re-bind instance Observed Node.
  • Lazy creation of Observed Node if need.

Master detail/ObservableValue

The first idea is to use Master detail concept.

Beans

IObserving/ILazyObserving

Observed Node instance change every time and can be null. So when IObservableValue must be created to observe the Node, Node cannot be use directly because it can be null on start and instance change evry time. The first concept is to use org.eclipse.core.databinding.IObserving interface to observe Node :

package org.eclipse.core.databinding.observable;

public interface IObserving {
  public Object getObserved();
}

In the diagram element case, IObserving is implemented like this :

IObserving diagramObserved = new IObserving() {
  public Object getObserved() {
    return document.getDocumentElement();
  }
};

To manage lazy observed Node, JFace DOM-SSE Databinding provides org.eclipse.ufacekit.core.databinding.instance.observable.ILazyObserving which extends IObserving and IObservedFactory :

package org.eclipse.ufacekit.core.databinding.instance.observable;

import org.eclipse.core.databinding.observable.IObserving;

public interface ILazyObserving extends IObserving, IObservedFactory {

}

org.eclipse.ufacekit.core.databinding.instance.observableIObservedFactory have IObservedFactory#createObserved() method which is called when observed Node cannot be find when another IObservableValue (In Shapes DOM-SSE Editor context, SWT TextObservable) whish update the value of observed Node (attribute value) :

package org.eclipse.ufacekit.core.databinding.instance.observable;

public interface IObservedFactory {
  Object createObserved();
}

In the diagram element case, ILazyObserving is implemented like this :

IObserving diagramObserved = new ILazyObserving() {
  public Object getObserved() {
    return document.getDocumentElement();
  }
  public Object createObserved() {
    Element diagram = document.createElement("diagram");
    return document.appendChild(diagram);
  }
};

IInstanceObservedContainer

JFace DOM-SSE Databinding manage the rebinding of observed Node instance if need. To manage that, the first concept is to have a container of observed instance which is enable to manage the problematic of change observed instance. JFace DOM-SSE Databinding provides the org.eclipse.ufacekit.core.databinding.instance.IInstanceObservedContainer interface :

package org.eclipse.ufacekit.core.databinding.instance;

import org.eclipse.core.databinding.observable.IObserving;

public interface IInstanceObservedContainer {

  void addObserving(IObserving observing, IInstanceObservedChanged changed);

  void observeInstances();

  void dispose();

}

IInstanceObservedContainer has 3 methods :

  • addObserving : this method register the #IObserving/ILazyObserving into the container and add it an event listener #IInstanceObservedChanged which is called as soon as Node instance change.
  • observeInstances : this method loop for each #IObserving/ILazyObserving which was registered and check if instance observed Node IObserving#getObserved() has change. If it has change, it call list of #IInstanceObservedChanged linked to the IObserving. Into DOM-SSE context, this method is called as soon as DOM change.
  • dispose : this method unregister the observing registered and remove listener if need. Into DOM-SSE context, it's very IMPORTANT to call it when EditorPart is closed, to remove listener.
IInstanceObservedChanged

IInstanceObservedChanged is event listener which is called by a IInstanceObservedContainer implementation, as soon as Node instance change.

package org.eclipse.ufacekit.core.databinding.instance;

public interface IInstanceObservedChanged {

  void instanceChanged(Object oldInstance, Object newInstance);
}
AbstractInstanceObservedContainer

IInstanceObservedContainer can be implemented with several way to manage Bean, EMF, DOM instance. The class base is org.eclipse.ufacekit.core.databinding.instance.AbstractInstanceObservedContainer which implements the 3 #IInstanceObservedContainer methods.

public abstract class AbstractInstanceObservedContainer implements IInstanceObservedContainer {  
...

  protected abstract void dispose(Object observed);

  protected abstract boolean isDirty(Object oldInstance, IObserving observing);
...

You must implements 2 methods :

  • dispose : if you wish for instance remove listener for each observed Node instance when IInstanceObservedContainer #dispose() is called.
  • isDirty : returns true if current Node instance (oldInstance) is dirty (instance has changed) and false otherwise.
StructuredModelInstanceObservedContainer

StructuredModelInstanceObservedContainer is abstract class container for SSE model. It extends AbstractInstanceObservedContainer and manage SSE Model. The constrctor of this class wait org.eclipse.wst.sse.core.internal.provisional.IStructuredModel instance. Into this constructor a org.eclipse.wst.sse.core.internal.provisional.IModelStateListener is added to the SSE model to call IInstanceObservedContainer#observeInstances() each time SSE model change :

private class InternalModelStateListener implements IModelStateListener {
 ...
  public void modelChanged(IStructuredModel model) {
    StructuredModelInstanceObservedContainer.super.observeInstances();
  }
 ...
}
DOMModelInstanceObservedContainer

DOMModelInstanceObservedContainer is class container for DOM-SSE model. It extends StructuredModelInstanceObservedContainer and manage DOM-SSE Model. It implements AbstractInstanceObservedContainer#isDirty(Object oldInstance, IObserving) like this :

  protected boolean isDirty(Object oldInstance, IObserving observing) {
    if (oldInstance == null)
      return true;
    return (((Node) oldInstance).getParentNode() == null);
  }

When Node as not parent Node, it means that Node is not attached to a DOM Document. This case comes when Node instance has changed.

ObservedValue/LazyObservedValue

ObservedValue
package org.eclipse.ufacekit.core.databinding.instance.observable.value;

import org.eclipse.core.databinding.observable.IObserving;
import org.eclipse.core.databinding.observable.Realm;
import org.eclipse.core.databinding.observable.value.WritableValue;
import org.eclipse.ufacekit.core.databinding.instance.IInstanceObservedChanged;

public class ObservedValue extends WritableValue implements
		IInstanceObservedChanged {

	private IObserving observing;

	public ObservedValue(Realm realm, IObserving observing) {
		super(realm, observing.getObserved(), null);
		this.observing = observing;
	}
	
	public ObservedValue(IObserving observing) {
		super(observing.getObserved(), null);
		this.observing = observing;		
	}

	public void instanceChanged(Object oldInstance, Object newInstance) {
		super.setValue(newInstance);
	}

	public IObserving getObserving() {
		return observing;
	}

}
LazyObservedValue
package org.eclipse.ufacekit.core.databinding.instance.observable.value;

import org.eclipse.core.databinding.observable.Realm;
import org.eclipse.ufacekit.core.databinding.instance.observable.ILazyObserving;
import org.eclipse.ufacekit.core.databinding.instance.observable.IObservedFactory;

public class LazyObservedValue extends ObservedValue implements
		IObservedFactory {

	private boolean creatingObserved = false;

	public LazyObservedValue(Realm realm, ILazyObserving observing) {
		super(realm, observing);
	}

	public LazyObservedValue(ILazyObserving observing) {
		super(observing);
	}

	public void instanceChanged(Object oldInstance, Object newInstance) {
		if (!creatingObserved)
			super.instanceChanged(oldInstance, newInstance);
	}

	public Object createObserved() {
		try {
			creatingObserved = true;
			return ((ILazyObserving) getObserving()).createObserved();
		} finally {
			creatingObserved = false;
		}
	}
}
InstanceObservables

InstanceObservables factory for IObservableValue :

package org.eclipse.ufacekit.core.databinding.instance;

import org.eclipse.core.databinding.observable.IObserving;
import org.eclipse.core.databinding.observable.value.IObservableValue;
import org.eclipse.ufacekit.core.databinding.instance.observable.ILazyObserving;
import org.eclipse.ufacekit.core.databinding.instance.observable.value.LazyObservedValue;
import org.eclipse.ufacekit.core.databinding.instance.observable.value.ObservedValue;

public class InstanceObservables {

	public static IObservableValue observeValue(
			IInstanceObservedContainer container, IObserving observing) {
		ObservedValue observableValue = createObservedValue(observing);
		container.addObserving(observing, observableValue);
		return observableValue;
	}

	private static ObservedValue createObservedValue(IObserving observing) {
		if (observing instanceof ILazyObserving) {
			return new LazyObservedValue((ILazyObserving) observing);
		}
		return new ObservedValue(observing);
	}

}

LazyMasterDetailObservables

Return an instance of LazyDetailObservableValue. Same code than DetailObservableValue but manage lazy mode of IObserving :

...
public void doSetValue(Object value) {
		if (innerObservableValue != null)
			innerObservableValue.setValue(value);
		else {
			// FIXME : Add code to manage lazy creation of observed instance...
			if (outerObservableValue instanceof IObservedFactory) {
				Object newObserved = ((IObservedFactory) outerObservableValue)
						.createObserved();
				if (newObserved != null) {
					updateInnerObservableValue(outerObservableValue,
							newObserved);
					if (innerObservableValue != null)
						innerObservableValue.setValue(value);
				}
			}
		}
	}

Why JFace DOM-SSE Databinding?

This project provides the capability to manage binding with DOM-SSE nodes (IDOMNode). It is based on JFace DOM Databinding. Why having JFace DOM-SSE Databinding although JFace DOM Databinding manage DOM bindings.? The answer is :

  • DOM event listener problem : INodeNotifier 2 EventTarget. JFace DOM Databinding use W3C DOM Event Model to observe DOM node change. On other words Node of DOM Document to bind must implement EventTarget. DOM-SSE have their own Event Model. Node of DOM-SSE Document implement INodeNotifier. Goal of JFace DOM-SSE Databinding is to adapt DOM-SSE event INodeNotifier to W3C DOM event EventTarget.
  • Instance nodes problem. JFace DOM Databinding provides several observable to observe a Node instance. If Node instance change, binding is broken. Into XML editor context, the XML is typed by user, DOM is every time broken. Node instances change every time, so it's difficult to observe a Node instance, because instance change every time. Goal of JFace DOM-SSE Databinding is enable to observe Nodes. If Node is removed (user remove the XML content) and recreated (user retype XML content), JFace DOM-SSE Databinding is enable to recreate observable to observe the new Node instance.

What is DOM-SSE?

DOM-SSE is W3c DOM Document comming from IFile or TextEditor. XML Editor from WTP which is based on StructuredTextEditor manage internally DOM-SSE. The DOM-SSE is updated as soon as user type XML content. DOM-SSE is getted from WST IDOMModel like this :

IFile file = ... 
IModelManager manager = StructuredModelManager.getModelManager(); 
IDOMModel model = (IDOMModel)manager.getExistingModelForRead(file); 
if (model == null) { 
  model = manager.getModelForRead(file); 
} 

Document document = model.getDocument();

Each Nodes of DOM Document implements org.eclipse.wst.xml.core.internal.provisional.document.IDOMNode interface which extends :

  • W3C org.w3c.dom.Node.
  • org.eclipse.wst.sse.core.internal.provisional.INodeNotifier.

DOM-SSE can be observed by using :

  • IDOMModel#addModelStateListener(IModelStateListener listener) : as soon as DOM-SSE is updated (add/remove/update any Nodes), you can use IModelStateListener#modelChanged(IStructuredModel model) to detect that :
    IDOModel model = ...
    model.addModelStateListener(new IModelStateListener(){
      ...
      public void modelChanged(IStructuredModel model) {
    	
      }
    });
  • org.eclipse.wst.sse.core.internal.provisional.INodeNotifier provides the capability to add event listener and observe change of the node.
    IDOMElement element = ...
    element.addAdapter(new INodeAdapter() {
      public boolean isAdapterForType(Object type) {
        return true;
      }
      public void notifyChanged(INodeNotifier notifier, int eventType,
        Object changedFeature, Object oldValue, Object newValue, int pos) {
        
        // Element has changed (attribute changed, ...)
        // Do something
    				
      }
    });