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Eclipse GMF Guide
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Layout Service Example

Introduction

This guide describes the Layout Service example in the SDK.  This example demonstrates a how to create a custom provider for the Layout Service which can be invoked from with-in a diagram editor.

Description

This plug-in is named org.eclipse.gmf.examples.runtime.diagram.layout.  The purpose of the plug-in is provide an action that invokes a custom layout.  In this case the custom layout is called a 'Square' layout which will calculate a square area based on the number of shapes and arrange the shapes in a grid with-in the calculated square.

The algorithm for this custom layout is defined inside a provider called 'SquareLayoutProvider'.  To register this provider, an extension for the org.eclipse.gmf.runtime.diagram.ui.layoutProviders extension point must be added to the plugin.xml file.

i.e.

   <extension
         point = "org.eclipse.gmf.runtime.diagram.ui.layoutProviders" >
      <layoutProvider              class = "org.eclipse.gmf.examples.runtime.diagram.layout.provider.SquareLayoutProvider" >
        
<Priority
               name = "Medium" >
         </Priority>
      </layoutProvider>
   </extension>

If we examine the 'SquareLayoutProvider' java class, in the provides() routine, it is merely checking to see if the nodes on the diagram can be laid-out according to the algorithm and also verifying that the layout type being passed through the ILayoutNodesOperation is of type 'SQUARE_LAYOUT'.  This check is necessary because we only want to invoke this layout when our specific action is called, not when a default arrange action is invoked.

The layoutNodes (?) routine is where the actual computation takes place.  It returns a 'Runnable' that performs the execution of the layout.

Usage

Refer to this example if you need:

  1. How to create a manipulate shapes positions programmatically
  2. How to create a custom layout provider that can be invoked through a specific action



Copyright (c) 2000,2005 IBM Corporation and others. All Rights Reserved.




 
 
  Published under the terms of the Eclipse Public License Version 1.0 ("EPL") Design by Interspire