paintComponent未绘制到JPanel上 [英] paintComponent not painting onto JPanel
问题描述
我正在做一项家庭作业，我应该制作一个程序，使您可以绘制自定义形状和线条，并在屏幕上移动它们.
I am working on a homework assignment where I am supposed to make a program that allows you to paint custom shapes and lines, and move them around the screen.
最初，我使用public void paint(g)进行绘画，但是当我调用repaint时，形状闪烁.
Originally I was using public void paint(g) to paint, but the shapes were flickering when I called repaint.
因此，我切换到了paintComponent(g).但是，当我尝试绘制形状时，没有任何显示.我相信这是因为它没有在JPanel上绘画.
Because of that I switched over to paintComponent(g). However When I try to paint a shape nothing shows up. I believe this is because it isn't painting on top of the JPanel.
框架在3行BorderLayout中具有3个面板.
The frame has 3 panels in a 3 row BorderLayout.
[Button JPanel]
[Draw Box JPanel]
[Coordinate Jpanel]
我想绘制的面板自然是"Draw Box"面板.
The panel I would like to draw on is the Draw Box panel, naturally.
这是我当前拥有的代码:
Here is the code I have currently:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenuBar;
import javax.swing.JPanel;
public class Main extends JPanel implements ActionListener, MouseListener, MouseMotionListener {
private String colors[] = { "Black", "Red", "Orange", "Yellow", "Green", "Blue" };
private String shapes[] = { "Ellipse", "Line", "Rectangle" };
private JMenuBar toolBar; // flow layout? OR box layout x-Axis
private JPanel drawBox;
private JPanel coordBox;
private JLabel coords;
private JButton undo = new JButton("Undo");
private JButton clear = new JButton("Clear");
private JComboBox color = new JComboBox(colors);
private JComboBox shape = new JComboBox(shapes);
private JCheckBox fill = new JCheckBox("Filled");
public Main() {
JFrame frame = new JFrame("Paint");
frame.setSize(400, 600);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
frame.setLayout(new BorderLayout());
/*
* SETUP TOOLBAR
*/
toolBar = new JMenuBar();
toolBar.setLayout(new GridLayout(1, 5));
toolBar.add(undo);
toolBar.add(clear);
toolBar.add(color);
toolBar.add(shape);
toolBar.add(fill);
/*
* ADD ACTION LISTENERS TO BUTTONS
*/
undo.addActionListener(this);
clear.addActionListener(this);
color.addActionListener(this);
shape.addActionListener(this);
fill.addActionListener(this);
/*
* SETUP DRAW BOX
*/
drawBox = new JPanel();
drawBox.setOpaque(true);
drawBox.setPreferredSize(new Dimension(600, 400));
drawBox.addMouseListener(this);
drawBox.addMouseMotionListener(this);
/*
* SETUP COORDINATES
*/
coords = new JLabel();
coordBox = new JPanel();
coordBox.setBackground(new Color(211, 211, 211));
coordBox.setPreferredSize(new Dimension(drawBox.getWidth(), 25));
coords.setText("Coords: [0,0]");
coords.addMouseMotionListener(this);
coordBox.add(coords);
/*
* ADD TO FRAME
*/
frame.add(toolBar, BorderLayout.NORTH);
frame.add(drawBox, BorderLayout.CENTER);
frame.add(coordBox, BorderLayout.SOUTH);
frame.pack();
}
public static void main(String[] args) {
Main m = new Main();
}
public void paintComponent(Graphics g) {
// super.paintComponent(g);
g.setColor(Color.BLACK);
g.fillRect(300, 300, 100, 100);
}
@Override
public void actionPerformed(ActionEvent e) {
if (e.getSource() == undo) {
System.out.println("Undo Last");
}
if (e.getSource() == clear) {
System.out.println("clearing screen");
}
// COLOR DROP DOWN BOX
if (e.getSource() == color) {
JComboBox cb = (JComboBox) e.getSource();
String selected = (String) cb.getSelectedItem();
switch (selected) {
case "Red":
System.out.println("switching to color red");
//ellipse.setColor(Color.RED);
break;
case "Orange":
System.out.println("switch to coor orange");
//ellipse.setColor(Color.ORANGE);
break;
case "Yellow":
System.out.println("switching to color yellow");
break;
case "Green":
System.out.println("Switching to green");
//ellipse.setColor(Color.GREEN);
break;
case "Blue":
System.out.println("Switching to blue");
break;
default:
System.out.println("NOthing selected");
break;
}
}
// SHAPE DROP DOWN BOX
if (e.getSource() == shape) {
JComboBox cb = (JComboBox) e.getSource();
String selected = (String) cb.getSelectedItem();
switch (selected) {
case "Ellipse":
System.out.println("switching to ellipse");
break;
case "Line":
System.out.println("switch to line");
break;
case "Rectangle":
System.out.println("switching to rectangle");
break;
default:
System.out.println("NOthing selected");
break;
}
}
if (e.getSource() == fill) {
JCheckBox cb = (JCheckBox) e.getSource();
if (cb.isSelected()) {
System.out.println("Fill shape");
//ellipse.setFilled(true);
} else {
System.out.println("Empty shape");
//ellipse.setFilled(false);
}
}
}
@Override
public void mouseClicked(MouseEvent arg0) {
// System.out.println("Mouse clicked");
}
@Override
public void mouseEntered(MouseEvent e) {
System.out.println("Mouse entered");
}
@Override
public void mouseExited(MouseEvent arg0) {
coords.setText("Coords: N/A");
}
@Override
public void mousePressed(MouseEvent arg0) {
System.out.println("Mouse pressed");
}
@Override
public void mouseReleased(MouseEvent arg0) {
System.out.println("Mouse Released");
}
@Override
public void mouseDragged(MouseEvent e) {
coords.setText("Coords: [" + e.getX() + "," + e.getY() + "]");
}
@Override
public void mouseMoved(MouseEvent e) {
coords.setText("Coords: [" + e.getX() + "," + e.getY() + "]");
// repaint();
// revalidate();
}
}
推荐答案
您的Main类扩展了JPanel，具有paintComponent方法-但是您从未将Main的实例添加到GUI ，而是在GUI上添加一个普通的JPanel，drawBox，当然，paintComponent将永远不会被调用.
Your Main class extends JPanel, has a paintComponent method -- but you never add an instance of Main to the GUI, instead you add a plain-vanilla JPanel, drawBox to the GUI, and so of course paintComponent will never be called.
解决方案:将Main或this添加到GUI，而不是普通的JPanel.
Solution: add Main or this to the GUI, not a plain JPanel.
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