Question

所以我刚刚开始学习java GUI，我有布局和组件，但我只是在事件处理方面很可怕。这是我第一个有意义的GUI项目，我迫切需要一些指导。我的布局很好，我只是不知道如何根据ComboBoxes中的选择绘制Rectangle，Oval或Line。到目前为止，这是我的代码：

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);

    }

}

Answer 1

首先看看

基本上，你需要某种表面来渲染你的形状。可能最简单的方法是使用JPanel并覆盖它的paintComponent方法。

对此我会附加你的MouseListener，因为你想要物理添加形状和鼠标事件的地方是生成它们的组件的上下文。

您需要提供一些方法，通过这些方法，控件可以告诉涂料表面＆＃34;画什么这可以通过一个简单的setter和一些商定的值来完成（比如enum或static final常量。）

当用户按下并释放鼠标时，您需要确定要创建的形状并将该形状添加到某种List，您需要调用repaint来通知重绘经理你希望你的组件重新粉刷。

调用paintComponent后，您将遍历形状列表并调用Graphics2D#draw和/或Graphics2D#fill，具体取决于您要对形状执行的操作。

您还可以查看this simular question以获取更多想法。

如何在JPanel上绘制2D形状

1 个答案: