java - 在对象之间切换时如何摆脱矩形内的圆圈

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我有一个组合框，我可以在其中选择绘制矩形、圆形或徒手绘制。如果我选择画一个圆圈，它就会完美地画出来。如果我然后切换到绘制一个矩形，它会在矩形内绘制一个圆。如果我首先选择绘制一个矩形然后绘制一个圆形，也会发生同样的情况。 (见下图)

我的问题是:

1. 如何在绘制圆形和矩形之间切换而不让圆形出现在矩形内？

2. 如何在拖动鼠标时显示矩形/圆形。我的意思是，在我释放鼠标单击之前，线条如何显示？

3. 为什么不能徒手绘图？

这是我的测试类:

import java.awt.*; 
import java.awt.event.*;
import java.util.*;
import javax.swing.*;

public class Lab6 extends JFrame implements ActionListener {
    int startX, startY, endX, endY, w, h;
    ArrayList<Shape> shapeList =  new ArrayList<Shape>();
    Container cp = getContentPane();

    private JPanel topPanel;
    private JComboBox comboBox;    
    private final String[] boxOptions = new String[] {"Rektangel", "Cirkel", "Frihand"};   


    public Lab6(String title) {
        super(title);
        this.setLayout(new BorderLayout());
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);        
        this.setSize(840, 500);    
        this.initComponents();
        this.setVisible(true);
    }


    private void initComponents() {
        topPanel = new JPanel(new GridLayout(1,2));     
        topPanel.setPreferredSize(new Dimension(0,40));

        comboBox = new JComboBox(boxOptions);
        comboBox.setSelectedIndex(0);          
        comboBox.addActionListener(this);                          

        topPanel.add(comboBox);
        this.add(topPanel, BorderLayout.PAGE_START);          
    }

    @Override
    public void paint(Graphics g) {
        for (Shape s : shapeList) {
            s.draw(g);
        }
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource().equals(comboBox)) {     
            JComboBox cb = (JComboBox)e.getSource();
            if (cb.getSelectedItem().equals("Rektangel")) {                
                cp.addMouseListener(new MouseAdapter() {            
                    @Override
                    public void mousePressed(MouseEvent e) {                   
                        startX = e.getX();     
                        startY = e.getY(); 
                    }
                    @Override
                    public void mouseReleased(MouseEvent e) {
                        endX = e.getX();
                        endY = e.getY();

                        int width = startX - endX;
                        int height = startY - endY;
                        w = Math.abs(width);
                        h = Math.abs(height);

                        Rectangle r =  new Rectangle(startX, startY, w, h);

                        shapeList.add(r);
                        repaint();
                    }
                });                  
            }
            else if (cb.getSelectedItem().equals("Cirkel")) {

                cp.addMouseListener(new MouseAdapter() {            
                    @Override
                    public void mousePressed(MouseEvent e) {                   
                        startX = e.getX();     
                        startY = e.getY(); 
                    }
                    @Override
                    public void mouseReleased(MouseEvent e) {
                        endX = e.getX();
                        endY = e.getY();

                        int width = startX - endX;
                        int height = startY - endY;
                        w = Math.abs(width);
                        h = Math.abs(height);

                        Circle c =  new Circle(startX, startY, w, h);

                        shapeList.add(c);
                        repaint();
                    }
                });   
            }
            else if (cb.getSelectedItem().equals("Frihand")) {   //I need help with this part

               cp.addMouseListener(new MouseAdapter() {            
                @Override
                public void mousePressed(MouseEvent e) {            
                    startX = e.getX();
                    startY = e.getY();
                }
                @Override
                public void mouseDragged(MouseEvent e) {

                    FreeHand fh =  new FreeHand(startX, startY, e.getX(), e.getY());

                    shapeList.add(fh);
                    repaint();
                }
            });  

            }
        }
    }

    public static void main(String args[]) {
        new Lab6("Drawing Program");
    }
}

在 Rectangle 类中(Circle 类看起来相同):

import java.awt.*;

public class Rectangle extends Shape {

    public Rectangle(int x, int y, int width, int height) {
        super(x, y, width, height);
    }

    public Rectangle() {
        super();
    }

    @Override
        public void draw(Graphics g) {  
            Graphics2D g2 = (Graphics2D) g;             
            g2.setColor(Color.RED);                     
            g2.setStroke(new BasicStroke(4));           
            g.drawRect(getX(), getY(), getWidth(), getHeight());       
    }        
}

在 FreeHand 类中(我需要这部分的帮助):

import java.awt.*;

public class FreeHand extends Shape {

    public FreeHand(int x, int y, int width, int height) {
        super(x, y, width, height);
    }

    public FreeHand() {
        super();
    }        

    @Override
    public void draw(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;             
        g2.setColor(Color.BLUE);                    
        g2.setStroke(new BasicStroke(4));           
        g2.drawLine(getX(), getY(), getWidth(), getHeight());  
    }
}

类形状:

import java.awt.Graphics;
import javax.swing.JPanel;

public abstract class Shape extends JPanel {

    private int startX, startY, width, height;    

    public Shape() {
        this(0, 0, 1, 1);
    }

    public Shape(int startX, int startY, int width, int height) {
        this.startX = startX;
        this.startY = startY;
        this.width = width;
        this.height = height;
    }

    public abstract void draw(Graphics g);

    @Override
    public int getX() {
        return startX;
    }

    @Override
    public int getY() {
        return startY;
    }

    @Override
    public int getWidth() {
        return width;
    }

    @Override
    public int getHeight() {
        return height;
    }
}

Answer 1

发生了很多事情......

1. 重写JFrame的paint
2. 在执行自定义绘制之前不调用 super.paint。
3. 每次更改形状时添加新的 MosueListener

相反，创建一个自定义组件，从JPanel之类的东西扩展，并覆盖它的paintComponent方法。使用此组件具有您的基本绘图表面(您的控件应包含在另一个组件中)。

确保在执行任何自定义绘制之前调用 super.paintComponent，这样就不会破坏绘制链

参见Performing Custom Painting和 Painting in AWT and Swing了解更多详情

创建一个MouseListener并将其注册到面板。当用户选择不同的形状时，更改面板内的状态变量(通过 setter )，该变量告诉 MouseListener 当用户开始绘图时它应该做什么。

已更新...

创建一个从 JPanel 扩展的自定义类...

public static class ShapePane extends JPanel {

}

重写类paintComponent方法...

public static class ShapePane extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

为布局管理器提供一些大小调整提示...

public static class ShapePane extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

    public Dimension getPreferredSize() {
        return new Dimension(200, 200);
    }

}

提供一种可以更改形状类型的方法...以便您知道要绘制什么...

public static class ShapePane extends JPanel {

    public enum ShapeType {

        CIRCLE,
        RECTANGLE
    }

    private ShapeType currentShapeType;

    public void setCurrentShapeType(ShapeType currentShapeType) {
        this.currentShapeType = currentShapeType;
    }

    public ShapeType getCurrentShapeType() {
        return currentShapeType;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

向自定义类添加一个 MouseListener 以创建所需的形状类型...

public static class ShapePane extends JPanel {

    public enum ShapeType {

        CIRCLE,
        RECTANGLE
    }

    private ShapeType currentShapeType;

    public ShapePane() {
        addMouseListener(new MouseAdapter() {

            private Point clickPoint;

            @Override
            public void mousePressed(MouseEvent e) {
                clickPoint = e.getPoint();
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                Point releasePoint = e.getPoint();
                int x = Math.min(releasePoint.x, clickPoint.x);
                int y = Math.min(releasePoint.y, clickPoint.y);
                int width = Math.abs(clickPoint.x - releasePoint.x);
                int height = Math.abs(clickPoint.y - releasePoint.y);
                switch (getCurrentShapeType()) {
                    case CIRCLE:
                        // Make a circle
                        break;
                    case RECTANGLE:
                        // Make a rectangle...
                        break;
                }
                repaint();
            }

        });
    }

    public void setCurrentShapeType(ShapeType currentShapeType) {
        this.currentShapeType = currentShapeType;
    }

    public ShapeType getCurrentShapeType() {
        return currentShapeType;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Custom Painting here...
    }

}

填空...

创建另一个JPanel(这次您可以简单地创建一个实例)，向其中添加您的控件

创建 JFrame 的实例，向其添加自定义类和控制面板(确保它们布局正确，这样它们就不会相互覆盖 - 有关更多信息，请参阅 Laying Out Components Within a Container详情)

使用适当的控件监听器来确定用户想要绘制的形状类型，并相应地设置 currentShapeType 属性...