如何在JPanel GridLayout上进行鼠标进入和鼠标退出？

Question

I have problem how to make mouse exit and mouse enter in GridLayout on JPanel which contain 2 Panels in 1 cell.

I don't know how to know which cell was enter on a grid layout, is there any function?

I have grid layout on container, for 5 rows and 3 columns, and what I want is a mouse listener to all the cells, so when I enter cell it would say which cell I am entering because of the mouse listener.

Any clues?

Answer 1

MouseEvent.getComponent() will return the component which generated the event. If the code adds a mouse listener to each of the panels in the grid, it is easy to find out which one fired the event.

import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;

public class MousePanelArrayTest {

    private final JComponent ui = new JPanel(new BorderLayout(4, 4));
    MouseListener mouseListener;

    MousePanelArrayTest() {
        initUI();
    }

    public final void initUI() {
        mouseListener = new MouseAdapter() {

            @Override
            public void mouseEntered(MouseEvent e) {
                Component c = e.getComponent();
                c.setBackground(Color.BLACK);
            }

            @Override
            public void mouseExited(MouseEvent e) {
                Component c = e.getComponent();
                c.setBackground(Color.WHITE);
            }
        };

        ui.setBorder(new EmptyBorder(4, 4, 4, 4));
        JPanel gridPanel = new JPanel(new GridLayout(0, 5, 4, 4));
        ui.add(gridPanel);
        for (int ii=0; ii<20; ii++) {
            gridPanel.add(getPanel());
        }
    }

    private JPanel getPanel() {
        JPanel p = new JPanel();
        p.addMouseListener(mouseListener);
        p.setBorder(new EmptyBorder(10, 20, 10, 20));

        return p;
    }

    public JComponent getUI() {
        return ui;
    }

    public static void main(String[] args) {
        Runnable r = () -> {
            try {
                UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
            } catch (Exception useDefault) {
            }
            MousePanelArrayTest o = new MousePanelArrayTest();

            JFrame f = new JFrame(o.getClass().getSimpleName());
            f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
            f.setLocationByPlatform(true);

            f.setContentPane(o.getUI());
            f.pack();
            f.setMinimumSize(f.getSize());

            f.setVisible(true);
        };
        SwingUtilities.invokeLater(r);
    }
}````

Answer 2

One way to do this would be to get the position of the mouse when it enters the grid layout and calculate the cell that this position belongs to. Becuase the grid layout only alows cells with the same size this could be easily calculated. In pseudocode:

event = the mouse event
position = event.getPosition()
panelPosition = position of the panel that includes the grid layout
relativePosition = [position.x - panePosition.x, position.y - panePosition.y]

//get width and height of the panel that includes the gridlayout
int width = pane.width 
int height = pane.height

int numRows = gridlayout.getRows()
int numCols = gridlayout.getCols()

int cellx = relativePosition.x / (width / numRows)
int celly = relativePosition.y / (height / numCols)
//the cell where the mouse is is [cellx, celly]

Here the MouseListener needs to be added to the panel that includes the GridLayout , because you can't add a MouseListener to the layout itselves (but the layout will have the same size like the panel, so it doesn't realy matter).

Another way would be to add a panel into every cell of the gridlayout and check whether the mouse entered one of this panels (of which you know the cell, because you added them to the layout).