用Java在鼠标点击上绘制一个形状

Question

我正在尝试创建一个 java 程序，当用户单击 Frame 时，它​​将在 JFrame 上绘制一个形状。我已经到了将其设置为接受不同形状并识别点击的地步，但我无法弄清楚如何实现形状的绘制。

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.*;
import javax.swing.JComponent;

public class StamperFrame extends JFrame {

    private JButton circleButton, ovalButton, squareButton, rectButton;
    private int buttonValue = 0;

    public StamperFrame() {
        setTitle("Shape Stamper");
        setSize(500, 500);

        //Setting up the buttons and positioning them.
        JPanel buttonPanel = new JPanel();

        circleButton = new JButton("Circle");
        ovalButton = new JButton("Oval");
        squareButton = new JButton("Square");
        rectButton = new JButton("Rectangle");

        buttonPanel.add(circleButton);
        buttonPanel.add(ovalButton);
        buttonPanel.add(squareButton);
        buttonPanel.add(rectButton);
        getContentPane().add(buttonPanel, BorderLayout.SOUTH);
        //end button init



        //Setting up button logic
        circleButton.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                buttonValue = 1;
                System.out.println(buttonValue);
            }
        });
        ovalButton.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                buttonValue = 2;
                System.out.println(buttonValue);
            }
        });
        squareButton.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                buttonValue = 3;
                System.out.println(buttonValue);
            }
        });
        rectButton.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                buttonValue = 4;
                System.out.println(buttonValue);
            }
        });
        //end button click configuration

        getContentPane().addMouseListener(new MouseAdapter() {

            @Override
            public void mouseClicked(MouseEvent e) {
                if (buttonValue == 1) {
                    System.out.println("Circle added at: " + e.getX() + "," + e.getY());
                } else if (buttonValue == 2) {
                    System.out.println("Oval added at: " + e.getX() + "," + e.getY());
                }else if (buttonValue == 3) {
                    System.out.println("Square added at: " + e.getX() + "," + e.getY());
                }else if (buttonValue == 4) {
                    System.out.println("Rectangle added at: " + e.getX() + "," + e.getY());
                }
            }
        });

    }
}

我知道它需要以某种方式在我的鼠标事件中起作用，但我不知道如何。

我的框架目前看起来像这样：http://puu.sh/8ELaR/c7252286c0.jpg

任何建议将不胜感激。

Answer 1

请参阅Custom Painting Approaches 了解自定义绘画的两种方法：

1. 将要绘制的对象添加到 ArrayList
2. 将对象直接绘制到 BufferedImage 上。

链接中的示例仅绘制了一个矩形，因此您显然需要修改代码以支持不同的形状，但它应该会给您一些想法。

Answer 2

好的。现在真正完整的回答：

TL;DR：复制并粘贴以下代码：

package FinalExam;

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

public class StamperFrame extends JFrame {

    private final JButton circleButton, ovalButton, squareButton, rectButton;

    private final JPanel shapesPanel;

    private Shape shape;
    private final int w = 100;
    private final int h = 200;

    private Object lastButtonPressed;

    public StamperFrame() {
        setTitle("Shape Stamper");
        setSize(500, 500);

        final Container contentPane = getContentPane();

        //Setting up the buttons and positioning them.
        JPanel buttonPanel = new JPanel();

        circleButton = new JButton("Circle");
        ovalButton = new JButton("Oval");
        squareButton = new JButton("Square");
        rectButton = new JButton("Rectangle");

        buttonPanel.add(circleButton);
        buttonPanel.add(ovalButton);
        buttonPanel.add(squareButton);
        buttonPanel.add(rectButton);

        contentPane.add(buttonPanel, BorderLayout.SOUTH);
        //end button init

        shapesPanel = new JPanel(){
            @Override
            public void paintComponent(Graphics graphics) {
                Graphics2D g = (Graphics2D) graphics;
                super.paintComponent(g); 
                if(shape != null) g.draw(shape);
            }

        };
        contentPane.add(shapesPanel, BorderLayout.CENTER);

        final ActionListener buttonPressed = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                lastButtonPressed = event.getSource();
            }
        };

        circleButton.addActionListener(buttonPressed);
        ovalButton.addActionListener(buttonPressed);
        squareButton.addActionListener(buttonPressed);
        rectButton.addActionListener(buttonPressed);

        contentPane.addMouseListener(new MouseAdapter() {

            @Override
            public void mouseClicked(MouseEvent e) {

                int x = e.getX();
                int y = e.getY();

                if(lastButtonPressed == circleButton){
                    shape = new Ellipse2D.Double(x, y, w, w);
                    echo("Circle",x,y);
                } else if(lastButtonPressed == ovalButton){
                    shape = new Ellipse2D.Double(x, y, w, h);
                    echo("Oval",x,y);
                } else if (lastButtonPressed == squareButton){
                    shape = new Rectangle2D.Double(x, y, w, w);
                    echo("Square",x,y);
                } else if (lastButtonPressed == rectButton){
                    echo("Rectangle",x,y);
                    shape = new Rectangle2D.Double(x, y, w, h);
                } 

                shapesPanel.repaint();
            }

            private void echo(String shape, int x, int y){
                System.out.println(shape + " added at: " + x + "," + y);
            }

        });

    }
}

详细解释

1. 我们不需要变量 buttonValue 来记住按下了哪个按钮。按钮是事件源，所以我们只需存储它，稍后我们就可以知道按下了哪个按钮。
2. 我们不需要 4 个 ActionListener 实例（每个按钮一个），因为它们都做同样的事情（将事件源存储为“按下的按钮”
3. 绘图技巧是通过使用JPanel（shapesPanel 变量）作为“绘图画布”来完成的。我们扩展 JPanel 以覆盖 paintComponent。该方法将使用Graphics2D的绘图API。
4. 在contentPane 处添加的ActionListener 将获得单击的x 和y 坐标，创建要绘制的Shape（基于最后一个lastButtonPressed），将其存储在变量@987654331 @ 并询问 shapesPanel 到 repaint() 本身。

Answer 3

您将在内容窗格中添加一个新的 JPanel，可能位于中心

JPanel drawingPanel = new JPanel();
getContentPane().add(drawingPanel, BorderLayout.CENTER);

然后，您将在每个按钮的动作侦听器代码中调用该代码来绘制 JPanel 的图形：

rectButton.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
           Graphics2D g = Graphics2D drawingPanel.getGraphics2D(); 
           g.draw(new java.awt.Rectangle(42,42,20,40);

        }
    });

等等……

您需要熟悉 Java2D 才能完成 FinalExam 包的工作。