For experts: mechanisms for advanced users

In Rogue Wave JViews, the position of a subgrapher (instance of IlvGrapher) is always calculated from the positions of the contents of the subgrapher. The position of the subgrapher is simply the position of the bounding box around its contents. This mechanism has side effects when performing layout: a subgraph will never appear fixed if its contents is laid out, because when a layout is applied to the contents of the subgraph, the bounding box, hence the position, of the subgraph changes. Depending on the applications, this may be an unwanted effect.

Normally, after the subgraph is laid out, its parent graph gets laid out, which eventually moves the entire subgraph to its final position. Therefore, in most cases, the unwanted position of the subgraph is only temporary and you can ignore the entire problem. However, in a few situations, you need to be aware of the effect, namely:

In all these situations, it is important that the subgraph remains at the old position even after its contents has been laid out. The implementation of IlvGrapher does not behave like this.

The solution is simply to move the subgraph back to its old position immediately after the subgraph has been laid out, just before the layout of its parent graph is started. The Recursive Layout allows you to install a subgraph correction interface that contains a correct method which is called exactly at this point. You install a subgraph correction interface in the following way:

layout.setSubgraphCorrectionInterface(
new IlvSubgraphCorrectionBarycenterFixed());

Effect of subgraph correction illustrates the effect of subgraph correction.

Two default implementations of IlvSubgraphCorrectionInterface are available:

These implementations of the subgraph correction interface do not correct the top-level graph, but only the nested subgraphs The instances can be shared between different instances of IlvRecursiveLayout.

Event listener layout is an advanced feature documented in Using event listeners. You need to understand that general description and the concept of layout listeners before you read this section. This section describes some specific details of the Recursive Layout related to layout listeners.

The application can listen for layout events sent by the Recursive Layout or by each sublayout individually. For example, a progress bar that displays the progress of the entire nested layout should listen for the layout events fired by the Recursive Layout itself, while an application that wants to detect when a specific sublayout of a subgraph is started or stopped should listen for the layout events sent by that particular sublayout.

To install a layout event listener at the Recursive Layout, call usually:

recursiveLayout.addGraphLayoutEventListener(listener);

To install a layout listener that receives the layout events of all sublayouts of the Recursive Layout, you can call:

recursiveLayout.addSubLayoutEventListener(listener);

Note that in this case, the listener is installed at the Recursive Layout instance (not at the sublayout instances) but receives the events from the sublayouts (not from the Recursive Layout). An internal mechanism makes sure that the events are forwarded to the listener.

Alternatively, you could traverse the nesting structure and install the same listener at all subgraph layouts. However, this would have two disadvantages: it requires more memory and you need to reinstall or update the listener whenever you change the layout of a subgraph or the nesting structure by adding or removing subgraphs. When you use addSubLayoutEventListener , updating the listener is not necessary in this case.