i copied a code in
http://wiki.apache.org/xmlgraphics-batik/BackgroundGlassPaneTutorial here
and tried playing with the code for practice and this is what i have came
up:
*** CODE ***
import javax.swing.*;
import org.apache.batik.dom.svg.SVGDOMImplementation;
import org.w3c.dom.DOMImplementation;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.apache.batik.swing.*;
import org.w3c.dom.events.*;
public class MapCanvas {
protected JSVGCanvas canvas;
protected JLabel target;
public MapCanvas(JPanel panel) {
panel.removeAll();
canvas = new JSVGCanvas();
canvas.setDocumentState(JSVGCanvas.ALWAYS_DYNAMIC);
canvas.setSize(400,400);
canvas.setDocument(buildDocument());
panel.add(canvas);
panel.repaint();
}
protected Document buildDocument() {
DOMImplementation impl =
SVGDOMImplementation.getDOMImplementation();
String svgNS = SVGDOMImplementation.SVG_NAMESPACE_URI;
Document doc = impl.createDocument(svgNS, "svg", null);
// get the root element (the svg element)
Element svgRoot = doc.getDocumentElement();
// set the width and height attribute on the root svg element
svgRoot.setAttributeNS(null, "width", "400");
svgRoot.setAttributeNS(null, "height", "400");
// create the array of rectangles
Element g = doc.createElementNS(svgNS, "g");
g.setAttributeNS(null, "id", "rectangles");
for (int x = 10; x < 200 ; x += 30) {
for (int y = 10; y < 200; y += 30) {
Element rectangle = doc.createElementNS(svgNS, "rect");
rectangle.setAttributeNS(null, "x", "" + x);
rectangle.setAttributeNS(null, "y", "" + y);
rectangle.setAttributeNS(null, "width", "20");
rectangle.setAttributeNS(null, "height", "20");
rectangle.setAttributeNS(null, "style", "fill:blue");
rectangle.setAttributeNS(null, "id", "rect: " + x + ", "+
y);
// attach the rectangle to the g element
g.appendChild(rectangle);
}
}
svgRoot.appendChild(g);
Element g2 = doc.createElementNS(svgNS, "g");
g.setAttributeNS(null, "id", "circles");
for (int x = 210; x < 400 ; x += 30) {
for (int y = 210; y < 400; y += 30) {
Element circle = doc.createElementNS(svgNS, "circle");
circle.setAttributeNS(null, "cx", "" + x);
circle.setAttributeNS(null, "cy", "" + y);
circle.setAttributeNS(null, "r", "10");
circle.setAttributeNS(null, "style", "fill:red");
circle.setAttributeNS(null, "id", "circle: " + x + ", "+ y);
// attach the rectangle to the g element
g2.appendChild(circle);
}
}
svgRoot.appendChild(g2);
return doc;
}
public void addGlassPane() {
String svgNS = SVGDOMImplementation.SVG_NAMESPACE_URI;
Document doc = canvas.getSVGDocument();
Element rectangle = doc.createElementNS(svgNS, "rect");
rectangle.setAttributeNS(null, "x", "0");
rectangle.setAttributeNS(null, "y", "0");
rectangle.setAttributeNS(null, "width", "400");
rectangle.setAttributeNS(null, "height", "400");
rectangle.setAttributeNS(null, "style",
"fill:none;pointer-events:fill");
rectangle.setAttributeNS(null, "id", "glasspane");
Element svgRoot = doc.getDocumentElement();
svgRoot.insertBefore(rectangle, doc.getElementById("rectangles"));
}
public void registerListeners(JLabel target) {
//this label provides feedback on the selected item
this.target = target;
// Gets an element from the loaded document.
// document is your SVGDocument
Element elt = canvas.getSVGDocument().getElementById("glasspane");
EventTarget t = (EventTarget)elt;
t.addEventListener("click", new GlassPaneClick(), false);
Element elt2 = canvas.getSVGDocument().getElementById("rectangles");
EventTarget t2 = (EventTarget)elt2;
t2.addEventListener("click", new ObjectClick(), false);
Element elt3 = canvas.getSVGDocument().getElementById("circles");
EventTarget t3 = (EventTarget)elt3;
t3.addEventListener("click", new CircleClick(), false);
}
public class GlassPaneClick implements EventListener {
public void handleEvent(Event evt) {
target.setText("Glasspane event
"+((Element)evt.getTarget()).getAttribute("id"));
target.repaint();
}
}
public class ObjectClick implements EventListener {
public void handleEvent(Event evt) {
target.setText("Rectangles event
"+((Element)evt.getTarget()).getAttribute("id"));
target.repaint();
}
}
public class CircleClick implements EventListener {
public void handleEvent(Event evt) {
target.setText("Circles event
"+((Element)evt.getTarget()).getAttribute("id"));
target.repaint();
}
}
}
*** END OF CODE ***
i don't know what's wrong. i get the error java.lang.NullPointerException in
the line:
t2.addEventListener("click", new ObjectClick(), false);
why am i having these errors?
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