Don’t Create Zero Row or Column Datasets in BKBaseGraph
A developer stopped by today asking me about a problem he was having using the BKBaseGraph as it was saying it couldn't lock the dataset for the change - a nasty exception. I got his code which had a section like this:
private void initGraph() { try { curveGraph = new BKBaseGraph(0, 1, BKBaseGraph.LINE); graphPanel.add(curveGraph, BorderLayout.CENTER); int pointCount = 10; // display the points in the graph curveGraph.resizeData(pointCount, 1); for (int row = 0; row < pointCount; row++) { curveGraph.setData(row, 0, (Math.random() * 100.0)); curveGraph.setRowLabel(row, "" + row); } } catch (Exception e) { e.printStackTrace(); } }
The problem comes in line 3 when you are trying to create a zero-row dataset. That's no good. You have to have non-zero rows and columns - default to nothing and let the graph figure it out. For example, it's better to simply say:
curveGraph = new BKBaseGraph(BKBaseGraph.LINE);
and let it go at that. Alternatively, if you know the numebr of rows, as it appears is the case here, you can put that in and skip the resize alltogether:
private void initGraph() { try { int pointCount = 10; curveGraph = new BKBaseGraph(pointCount, 1, BKBaseGraph.LINE); graphPanel.add(curveGraph, BorderLayout.CENTER); // display the points in the graph for (int row = 0; row < pointCount; row++) { curveGraph.setData(row, 0, (Math.random() * 100.0)); curveGraph.setRowLabel(row, "" + row); } } catch (Exception e) { e.printStackTrace(); } }
Either way works, but don't put the zero rows or zero columns.
He came back to me and asked: OK, but how do I display no data on the graph? Well, there are methods on the BKBaseGraph that handle that:
curveGraph.hideGraph(); // ... curveGraph.showGraph();
the first hides the graph behind a blank white JPanel, and the second brings it to the front. This is useful if you have a lot of updates to do, or you simply want to say "no data - no graph." Simple as that.