Starting with yFiles version 2.3, method ShortestPaths.kShortestPathsCursor(y.base.Graph, y.base.DataProvider, y.base.Node, y.base.Node, int) can be used to successively return all possible shortest paths between two nodes. The static method finds the first k paths (where k is given by the last parameter) connecting a pair of nodes in a directed graph and having least costs. It returns a special YCursor object to iterate over these paths in a suitable fashion.

To get hold of all proper shortest paths, the returned cursor can be used to iterate over the k paths until a path is returned with costs larger than the first one (which is a proper shortest path). This technique is demonstrated in the sample code fragment below.
What the sample code does:

• First, intitializes the static method to return an unbound number of shortest paths between the two nodes.
• Then uses the costs of the first returned path as an indicator and iterates over the remaining paths until the costs of the current path exceed those of the first.
• Stores each proper shortest path encountered into a list.

// To hold an edge list for every path. 
YList allShortestPaths = new YList();

// The actual number of proper shortest paths is unknown, so we start with a really great value for 'k'. 
YCursor pathCursor = ShortestPaths.kShortestPathsCursor(graph, edgeCostsDP, startNode, endNode, Integer.MAX_VALUE);
if (pathCursor.ok())
{
  // The first path between the two nodes having least costs. 
  final EdgeList firstPath = (EdgeList)pathCursor.current();
  final double costsOfFirstPath = calculateCostsForPath(firstPath, edgeCostsDP);
  
  allShortestPaths.add(firstPath);
  pathCursor.next();
  
  // Look further. 
  while (pathCursor.ok())
  {
    EdgeList currPath = (EdgeList)pathCursor.current();
    double currCosts = calculateCostsForPath(currPath, edgeCostsDP);
    // If the current path is also a proper shortest path with costs equal to those 
    // of the first path, then add it to the list. 
    if (!(currCosts > costsOfFirstPath))
    {
      allShortestPaths.add(currPath);
      pathCursor.next();
    }
    else
      break;
  }
}

See the Javadoc API description for class ShortestPaths for more information on the yFiles library's shortest path algorithms.