Question

所以我正在制作一个绘图程序，它通过从IRC服务器聊天室输入命令来绘制。所以除了绘图之外的所有东西都可以工作并且我检查了它（你可以看到检查系统：P）但是drawLine（）命令并没有做它的事情。请帮忙！

PS：这是项目中的一个类文件，发送到这里的所有其他工作都信任我！

代码：

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

class PadDraw extends JComponent
{
    //this is gonna be your image that you draw on
    Image image;
    //this is what we'll be using to draw on
    Graphics2D graphics2D;
    //these are gonna hold our coordinates
    int currentX = 0, currentY = 0, oldX = 0, oldY = 0;

public PadDraw()
{

}

public void onCommand(String msg)
{
    if(msg.equalsIgnoreCase("up"))
    {

        if(oldY > 0)
        {
            currentY = currentY - 30;
            if(graphics2D != null)
            graphics2D.drawLine(oldX, oldY, currentX, currentY);
            repaint();
            oldX = currentX;
            oldY = currentY;
        }
    }
    if(msg.equalsIgnoreCase("down"))
    {
        if(oldY < 861)
        {
            System.out.println(msg);
            System.out.println("Starting Y: " + currentY);
            currentY = currentY + 30;
            System.out.println("Ending Y: " + currentY);
            if(graphics2D != null)
            graphics2D.drawLine(oldX, oldY, currentX, currentY);
            repaint();
            oldX = currentX;
            oldY = currentY;
            System.out.println("Old Y: " + oldY);
        }
    }
    if(msg.equalsIgnoreCase("left"))
    {
        if(oldX > 0)
        {
            currentX = currentX - 30;
            if(graphics2D != null)
            graphics2D.drawLine(oldX, oldY, currentX, currentY);
            repaint();
            oldX = currentX;
            oldY = currentY;
        }
    }
    if(msg.equalsIgnoreCase("right"))
    {
        if(oldX < 847)
        {
            currentX = currentX + 30;
            if(graphics2D != null){
            graphics2D.drawLine(oldX, oldY, currentX, currentY);
            repaint();
            }
            oldX = currentX;
            oldY = currentY;
        }
    }
}

public void paintComponent(Graphics g)
{
if(image == null)
{
image = createImage(getSize().width, getSize().height);
graphics2D = (Graphics2D)image.getGraphics();
graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

clear();
}

g.drawImage(image, 0, 0, null);
}

Answer 1

您忘记在super.paintComponent方法中调用paintComponent。有些人会错误地将其排除在外，以其正确的方式来实现“连续”绘画，但你实际所做的是打破油漆链，以及你是什么实际上看到的是油漆工件，这会让你相信有连续的油漆功能。
你这样做的方式不会产生“连续”的画。首先，您甚至没有将行绘制到JComponent图形上下文中。其次，一旦你在super.paintComponent方法中正确地调用了paintComponent，你就会丢失之前的一幅画

以下是可以/应该做的事情，而不是......

拥有Line2D个对象的列表。

List<Line2D> lines = new ArrayList<>();

循环List方法中的paintComponent并绘制它们

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;
    ...
    for (Line2D line : lines) {
        g2.draw(line);
    }
}

哦顺便说一下，paintComponent应该是protected而不是public

如果您想在图纸中添加一行，只需将另一个Line2D对象添加到列表中，然后repaint()
```
lines.add(new Line2D.Double(x1, y1, x2, y2));
repaint();
```

点击Line2D API和Graphics2D tutorial

Java drawLine命令不在屏幕上绘制

1 个答案:

以下是可以/应该做的事情，而不是......