GMF关于采用拖动方式创建连线的实例

场景：A1 A2两个容器，分别有隔间，隔间分别容纳B1 B2两种对象，任意B1和B2之间可以单向连线（即B1-〉B2）。

问题：为了更好的用户体验，需要直接拖动A1内的B1到B2上方Drop时候，创建连线C。

解决路径：

1、A1隔间内B1可拖动，给A1隔间安装：installEditPolicy(EditPolicy.LAYOUT_ROLE, new FlowLayoutEditPolicy()....

2、A2隔间可响应拖动，给A2隔间安装：

 installEditPolicy(EditPolicyRoles.DRAG_DROP_ROLE,
				new DragDropEditPolicy() {

					protected Command getDropElementCommand(EObject element,
							DropObjectsRequest request) {

						B2EditPart ep = findB2EditPartFromPoint(request
								.getLocation());
						setDropB2EditPart(ep); //自定义方法，记录拖动到的EP

						if (ep == null)
							return null;
						IElementType type = XXXElementTypes.CConnection_4001;
						CreateRelationshipRequest req = new CreateRelationshipRequest(
								element, ep.resolveSemanticElement(),
								type);
						ConnectionViewAndElementDescriptor viewDescriptor = new ConnectionViewAndElementDescriptor(
								new CreateElementRequestAdapter(req),((IHintedType) type).getSemanticHint(),
								XXXDiagramEditorPlugin.DIAGRAM_PREFERENCES_HINT);

						CreateConnectionViewAndElementRequest verequest = new CreateConnectionViewAndElementRequest(
								viewDescriptor);

						EditPart sourceEditPart = XXXBaseItemSemanticEditPolicy
								.getDiagramEditPart(getHost()).findEditPart(
										null, element);

						 // create the subtopics link command
						 ICommand createSubTopicsCmd = new
						 DeferredCreateConnectionViewAndElementCommand(verequest,
						 new EObjectAdapter((EObject) sourceEditPart.getModel()),
						 new EObjectAdapter(ep.getPrimaryView()),
						 getHost().getViewer());
			
						 return new ICommandProxy(createSubTopicsCmd);
					}
				});

 

 

 

        //根据拖动的位置找B2的方法
	private B2EditPart findB2EditPartFromPoint(Point pt) {
		EditPart ep = this.getRoot().getViewer().findObjectAt(pt);
		if (ep instanceof B2EditPart)
			return (B2EditPart) ep;
		else if (ep.getParent() instanceof AttributeEditPart) {
			return (B2) ep.getParent();
		}
		return null;
	}

3、A2隔间的A2CompartmentItemSemanticEditPolicy中，响应创建元素Request

 

	protected Command getCreateCommand(CreateElementRequest req) {
			
                //.........以上为自动生成代码

		if (XXXElementTypes.CConnection_4001 == req.getElementType()) {
			EObject target = null;

			if (getHost() instanceof A2CompartmentEditPart) {
				A2CompartmentEditPart) part = (B2CompartmentEditPart) getHost();

				B2EditPart ep = part.getDropB2EditPart();
				if (ep != null)
					target = ep.resolveSemanticElement();
				else
					return null;
				CreateRelationshipRequest req1 = new CreateRelationshipRequest(
						req.getNewElement(), target, req.getElementType());

				B2ItemSemanticEditPolicy poc = (B2ItemSemanticEditPolicy) ep
						.getEditPolicy(EditPolicyRoles.SEMANTIC_ROLE);
				Command cmd1 = poc.getCompleteCreateRelationshipCommand(req1); //此方法最终传导到了XXXBaseItemSemanticEditPolicy
				return cmd1;
			}

		}

		return super.getCreateCommand(req);
}

 

 

4、XXXBaseItemSemanticEditPolicy中完成getCreateRelationshipCommand

protected Command getCreateRelationshipCommand(CreateRelationshipRequest req) {

		if (req.getSource()!=null&&req.getTarget()!=null){
		CConnectionCreateCommand cmd = new CConnectionCreateCommand(req,
				req.getSource(), req.getTarget());

		return new ICommandProxy(cmd);
		}
		return null;
	}