JMapViewer，MouseListener调用了2次

Question

Working with JMapViewer, a strange behavior of the component was recognized. I am using DefaultMapController to get the map position (lat, lon).

import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import org.openstreetmap.gui.jmapviewer.DefaultMapController;
import org.openstreetmap.gui.jmapviewer.JMapViewer;

public class Test extends JMapViewer{

public Test() 
{
    addMouseListener(new DefaultMapController(this) {
            public void mouseClicked(MouseEvent e){
            Point  start = e.getPoint();
            System.out.println(e.getPoint());
            }            
       });
  }

protected void paintComponent(Graphics g){super.paintComponent(g);}  

public static void main (String [] args){
            JFrame jf = new JFrame();
            jf.setSize(800, 600);
            Test t= new Test();
            jf.add(t);
            jf.setVisible(true);
    }
}

Running the code, after the left mouse button is pressed, the method mouseClicked() gets called multiple times (2x). After the replacement

    addMouseListener(new DefaultMapController(this) {

with

    addMouseListener(new MouseAdapter() {

the code works correctly, the method gets called only 1x. Where is the problem? Is it a bug inside the library or the syntax is wrong or unsafe? How to avoid this issue? Thanks for your help.

Answer 1

Your Test extends JMapViewer , adding a MouseListener in an instance initializer block. As a consequence , the "default constructor will call the no-argument constructor of the superclass." The superclass, JMapController , adds your MouseListener —you guessed it—a second time.

public JMapController(JMapViewer map) {
    this.map = map;
    if (this instanceof MouseListener)
        map.addMouseListener((MouseListener) this);
    …
}

Instead, create a new JMapController or DefaultMapController , as shown here , and use it to construct your JMapViewer .

import java.awt.EventQueue;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import org.openstreetmap.gui.jmapviewer.DefaultMapController;
import org.openstreetmap.gui.jmapviewer.JMapViewer;

/**
 * @see https://stackoverflow.com/a/39461854/230513
 */
public class TestMapController {

    private void display() {
        JFrame f = new JFrame("TestMapController");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JMapViewer map = new JMapViewer();
        new DefaultMapController(map) {
            @Override
            public void mouseClicked(MouseEvent e) {
                System.out.println(e.getPoint());
            }
        };
        f.add(map);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new TestMapController()::display);
    }
}