In this section, you will learn what a LayoutController is and how to create and apply one to a VisualGraphView.

The layout of a VisualGraphView is delegated to a LayoutController component. This is not the same kind of “controller” that is described in the MVC tutorial in this manual. Rather it is an engine that manages the state of a layout activity, both during and after the completion of a visual graph. Moreover, the controller internally delegates certain responsibilities to a specialized Layout component that callers may specify using predefined string constants (also known as types).

Classes which implement the VisualGraphView interface provide a drawing area for visual graphs and as such utilize a LayoutController to automatically position visual graph elements relative to each another. Once you have retrieved this LayoutController from a view, you may set the layout “type” and/or directly call its apply() method to trigger the layout task. Remember to follow through with a call to the updateView() method, as shown in this example:

// get a reference to the layout controller
GraphLayoutController layoutController =
  (GraphLayoutController) graphView.getLayoutController();
    
// actually apply the layout
layoutController.apply(GraphLayoutController.Circular);

// center the graph in the middle of the view
VisualOperations.translateViewportAccordingToGraph(graphView);

In the example above, the layout type “Circular” is passed in a separate call and specifies a specific layout from the Tensegrity Graph API. This type constant is used to internally instantiate a specific Layout component which does the actual layouting. These layout types can also be contextualized with specific parameters called a “layout context”. Please see the following sections and our javadocs for more complete information about these topics.

// create a layout controller
GraphLayoutController layoutController = 
    new GraphLayoutController();
    
// disable animation
layoutController.enableAnimation(false);

As the above example shows, a LayoutController instance is created by instantiating a class derived from the abstract base class LayoutController. The GraphLayoutController instance is one of four out-of-the-box concrete LayoutController classes which provide a specific kind of runtime layout control. Please read our javadocs for more detailed information about the LayoutController base and derived classes.

When working with a VisualGraphView, it is necessary to assign a specific LayoutController to it. Below you can see just how to do that.

// set the newly created layout controller
graphView.setLayoutController( layoutController);