所以我刚刚开始学习java GUI，我已经有了布局和组件，但我在事件处理方面很糟糕。这是我的第一个有意义的 GUI 项目，我迫切需要一些指导。我的布局已经准备好了，我只是不知道如何让它根据组合框中的选择绘制矩形、椭圆形或线条。这是到目前为止我的代码:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.awt.Graphics2D;
import java.util.ArrayList;
public class PaintApp extends JFrame {
private int x, y, posX, posY, width, height;
private Graphics2D g;
private JButton undo;
private JButton clear;
private JComboBox color;
private JComboBox shape;
private JCheckBox fill;
private JLabel statusBar;
private static final String[] pickColor =
{"Black", "Blue", "Green", "Red"};
private static final String[] pickShape =
{"Line", "Oval", "Rectangle"};
PaintApp(){
super("Paint");
// north panel
JPanel buttonPanel = new JPanel();
undo = new JButton("Undo");
buttonPanel.add(undo);
add(buttonPanel, BorderLayout.NORTH);
clear = new JButton("Clear");
buttonPanel.add(clear);
add(buttonPanel, BorderLayout.NORTH);
color = new JComboBox(pickColor);
buttonPanel.add(color);
add(buttonPanel, BorderLayout.NORTH);
color.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
if(color.getSelectedItem().equals("Red")){
System.out.println("Color: " + color.getSelectedItem());
}else if(color.getSelectedItem().equals("Blue")){
System.out.println("Color: " + color.getSelectedItem());
}else if(color.getSelectedItem().equals("Green")){
System.out.println("Color: " + color.getSelectedItem());
}else if(color.getSelectedItem().equals("Black")){
System.out.println("Color: " + color.getSelectedItem());
}
}
});
shape = new JComboBox(pickShape);
buttonPanel.add(shape);
add(buttonPanel, BorderLayout.NORTH);
shape.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
if(shape.getSelectedItem().equals("Line")){
System.out.println("Shape: " + shape.getSelectedItem());
}else if(shape.getSelectedItem().equals("Oval")){
System.out.println("Shape: " + shape.getSelectedItem());
}else {
System.out.println("Shape: " + shape.getSelectedItem());
}
}
});
fill = new JCheckBox("Filled");
buttonPanel.add(fill);
add(buttonPanel, BorderLayout.NORTH);
// center panel
JPanel paintPanel = new JPanel();
paintPanel.setBackground(Color.WHITE);
add(paintPanel, BorderLayout.CENTER);
// south panel
statusBar = new JLabel("Mouse is off the canvas!");
add(statusBar, BorderLayout.SOUTH);
// mouse handler
MouseHandler handler = new MouseHandler();
paintPanel.addMouseListener(handler);
paintPanel.addMouseMotionListener(handler);
buttonPanel.addMouseListener(handler);
buttonPanel.addMouseMotionListener(handler);
}
private class MouseHandler implements MouseInputListener {
public void mouseDragged(MouseEvent e) {
statusBar.setText(String.format("(%d,%d)",
e.getX(), e.getY()));
}
public void mouseMoved(MouseEvent e) {
statusBar.setText(String.format("(%d,%d)",
e.getX(), e.getY()));
}
public void mouseClicked(MouseEvent e) {
String x = String.valueOf(color.getSelectedItem());
}
public void mousePressed(MouseEvent e) {
posX = e.getX();
posY = e.getY();
width = posX - x;
height = posY - y;
}
public void mouseReleased(MouseEvent e) {
posX = e.getX();
posY = e.getY();
width = posX - x;
height = posY - y;
}
public void mouseEntered(MouseEvent e) {
}
public void mouseExited(MouseEvent e) {
statusBar.setText("Mouse is off the canvas!");
}
}
}
public interface MyShape {
void draw(Graphics2D g);
}
public class MyRect extends Rectangle2D.Float implements MyShape{
Graphics2D g;
int x, y, posX, posY;
Color color;
MyRect(Graphics2D g, int x, int y, int posX, int posY, Color color){
this.g = g;
this.x = x;
this.y = y;
this.posX = posX;
this.posY = posY;
this.color = color;
}
public void draw(Graphics2D g){
g = (Graphics2D) g;
g.setColor(color);
g.drawRect(x, y, (posX - x), (posY - y));
}
}
public class MyOval extends Ellipse2D.Float implements MyShape{
Graphics2D g;
int x, y, posX, posY;
Color color;
MyOval(Graphics2D g, int x, int y, int posX, int posY, Color color){
this.g = g;
this.x = x;
this.y = y;
this.posX = posX;
this.posY = posY;
this.color = color;
}
public void draw(Graphics2D g){
g = (Graphics2D) g;
g.setColor(color);
g.drawOval(x, y, (posX - x), (posY - y));
}
}
public class MyLine extends Line2D.Float implements MyShape{
Graphics2D g;
int x, y, posX, posY;
Color color;
MyLine(Graphics2D g, int x, int y, int posX, int posY, Color color){
this.g = g;
this.x = x;
this.y = y;
this.posX = posX;
this.posY = posY;
this.color = color;
}
public void draw(Graphics2D g){
g = (Graphics2D) g;
g.setColor(color);
g.drawLine(x, y, (posX - x), (posY - y));
}
}
public static void main(String[] args){
PaintApp p = new PaintApp();
p.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
p.setSize(700,700);
p.setResizable(false);
p.setVisible(true);
}
}
最佳答案
首先看一下
基本上，您需要某种表面来渲染形状。也许最简单的方法是使用 JPanel 并重写它的 paintComponent 方法。
为此，我将附加您的 MouseListener，因为您想要物理添加形状和鼠标事件的位置与生成它们的组件相关。
您需要提供一些方法来让控件告诉“绘制表面”要绘制什么。这可以通过一个简单的 setter 和一些商定的值(例如 enum 或 static final 常量)来完成。
当用户按下并释放鼠标时，您将需要确定要创建什么形状并将该形状添加到某种List中，您将需要调用repaint 通知重绘管理器您希望重绘组件。
当调用 paintComponent 时，您将循环遍历形状列表并调用 Graphics2D#draw 和/或 Graphics2D#fill，具体取决于你想用这个形状做什么...
您还可以查看this simular question获取更多想法。
关于java - 如何在 JPanel 上绘制 2D 形状，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/26665932/