通过按钮将矩形绘制到画布上

Posted 2023-03-27

【中文标题】通过按钮将矩形绘制到画布上

【英文标题】：Painting a Rectangle to a Canvas via Button

【发布时间】：2020-10-13 19:12:22

【问题描述】：

这里有个小问题。我希望在单击按钮时在画布上绘制文本。我需要像 PaintEvent 这样的东西还是必须更新画布？如果我覆盖 DrawFrame.java 中的方法paint，我会打印出文本，但如果我单击按钮，我希望它发生。

我不允许使用 Swing、FX 或其他。仅 AWT。

这是我的两个课程：

import java.awt.*;
import java.awt.event.*;

public class DrawMain extends Frame 
    Panel pa1;
    Button bu1;
    Button bu2;
    Button bu3;
    
    public static void main(String[] args) 
        DrawMain dm = new DrawMain();
    
    
    public DrawMain() 
        super("Draw Main");
        
        setLocation(0, 8);
        setSize(250, 300);
        
        DrawFrame df = new DrawFrame();
        
        bu1 = new Button("Draw");
        bu2 = new Button("Clear");
        bu3 = new Button("Exit");
        
        bu1.addActionListener(
            new ActionListener() 
                public void actionPerformed(ActionEvent e) 
                    System.out.println(e.getActionCommand());
                    df.ca1 = new Canvas() 
                        public void paint(Graphics g) 
                            g.drawString("Sample Text", 10, 10);
                        
                    ;
                    df.ca1.repaint();
                
            
        );
            
        bu2.addActionListener(
            new ActionListener() 
                public void actionPerformed(ActionEvent e) 
                    System.out.println(e.getActionCommand());
                    
                
            
        );
            
        bu3.addActionListener(
            new ActionListener() 
                public void actionPerformed(ActionEvent e) 
                    System.out.println(e.getActionCommand());
                    System.exit(0);
                
            
        );
            
        pa1 = new Panel();
        pa1.setSize(this.getSize());
        pa1.setLayout(new GridLayout(3, 1));
        
        pa1.add(bu1);
        pa1.add(bu2);
        pa1.add(bu3);
        
        add(pa1);
        
        addWindowListener( 
            new WindowAdapter() 
                @Override
                public void windowClosing (WindowEvent e)  
                    System.exit(0); 
                
             
        );
        
        setVisible(true);
    

import java.awt.*;
import java.awt.event.*;

public class DrawFrame extends Frame 
    Panel pa1;
    Canvas ca1;
    
    public DrawFrame() 
        super("Draw Frame");
        
        setLocation(260, 8);
        setSize(1000, 750);
        
        ca1 = new Canvas();
        ca1.setBackground(Color.GREEN);
        ca1.setSize(this.getSize());

        pa1 = new Panel();
        pa1.setSize(this.getSize());
        pa1.setLocation(this.getLocation());
        
        pa1.add(ca1);
        
        add(pa1);
        
        addWindowListener( 
            new WindowAdapter() 
                @Override
                public void windowClosing (WindowEvent e)  
                    System.exit(0); 
                
             
        );
        
        setVisible(true);
    

【参考方案1】：

我已经有十多年没有使用 AWT 了，但你可以试试这个。这是一种使用按钮绘制字符串的简单方法。

public class ButtonDraw extends Panel 
    Frame f = new Frame();
    boolean draw = false;
    
    public static void main(String[] args) 
        new ButtonDraw();
        
    
    
    public ButtonDraw() 
        setPreferredSize(new Dimension(200, 200));
        f.add(this);
        f.addWindowListener(new MyWindowListener());
        // center on screen
        f.setLocationRelativeTo(null);
        Button b = new Button("Draw");
        add(b);
        b.addActionListener(ae -> 
            draw = true;
            repaint();
        );
        f.pack();
        f.setVisible(true);
    
    
    @Override
    public void paint(Graphics g) 
        super.paint(g);
        if (draw) 
            g.drawString("Drawing a String", 40, 100);
        
    
    private class MyWindowListener extends WindowAdapter 
        @Override
        public void windowClosing(WindowEvent we) 
            System.exit(0);