好吧所以我添加了推荐的更改，但是它（draggedMouse）似乎仍然没有与画布连接，即使我认为我做得对。我想它没有贴在画布上，但是我不知道如何去做。我为自己的无能而提前道歉！我还包括了我的Line类
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.ArrayList;
public class WholePanel extends JPanel
{
private Color currentColor;
private CanvasPanel canvas;
private JPanel leftPanel;
private JButton undo,erase;
private ArrayList<Line> lineList;
private Point ptStart,ptEnd, ptDrag;
private JRadioButton black,red,blue,green,orange;
private ArrayList<Line> drag;
public WholePanel()
{
currentColor = Color.black;
lineList = new ArrayList();
drag = new ArrayList();
undo = new JButton ("Undo"); // undo button
erase = new JButton("Erase"); // Erase button
black = new JRadioButton("Black"); black.setSelected(true); // setting black to the default line color
red = new JRadioButton("Red");
blue = new JRadioButton("Blue");
green = new JRadioButton("Green");
orange = new JRadioButton("Orange");
ButtonGroup group = new ButtonGroup(); // added buttons to group so only one can be selected at a time
group.add(black);
group.add(red);
group.add(blue);
group.add(green);
group.add(orange);
leftPanel = new JPanel(); // creates new JPanel that I can use to set the grid layout in and add the radio buttons
leftPanel.setLayout(new GridLayout(7,1));
leftPanel.add(black);
leftPanel.add(red);
leftPanel.add(blue);
leftPanel.add(green);
leftPanel.add(orange);
leftPanel.add(undo); // adds the undo button to the left panel above the erase button
leftPanel.add(erase); // adds the erase button to the left panel at the bottom
canvas = new CanvasPanel(); // creates the canvas panel
JSplitPane sp = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, leftPanel, canvas); // splits the applet layout into two panels
setLayout(new BorderLayout());
add(sp);
undo.addActionListener( new ButtonListener()); // adding listener action for undo and erase buttons
erase.addActionListener( new ButtonListener());
black.addActionListener( new ComboListener()); // adding listener actions for radio buttons
red.addActionListener( new ComboListener());
blue.addActionListener( new ComboListener());
green.addActionListener( new ComboListener());
orange.addActionListener( new ComboListener());
//canvas.addMouseListener(new PointListener());
//canvas.addMouseMotionListener(new PointListener());
PointListener pl = new PointListener(canvas.getGraphics());
canvas.addMouseListener(pl);
canvas.addMouseMotionListener(pl);
}
//CanvasPanel is the panel where shapes will be drawn
private class CanvasPanel extends JPanel
{
//this method draws all shapes specified by a user
public void paintComponent(Graphics page)
{
super.paintComponent(page);
setBackground(Color.WHITE);
for(int i = 0; i< lineList.size(); i++){
(lineList.get(i)).draw(page);
}
}
} //end of CanvasPanel class
//ButtonListener defined actions to take in case
//"Undo", or "Erase" is chosen.
private class ButtonListener implements ActionListener
{
public void actionPerformed (ActionEvent event)
{
JButton source = (JButton)event.getSource();
String name = source.getText();
if (name.equals("Undo"))
{
if(lineList.size() > 0)
{
lineList.remove(lineList.size()-1);
}
}
else if (name.equals("Erase"))
{
lineList.clear();
}
repaint();
}
} // end of ButtonListener
// listener class to set the color chosen by a user using
// the color radio buttons
private class ComboListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
JRadioButton src = (JRadioButton)event.getSource();
String name = src.getText();
if(name.equals("Black"))
{
currentColor = Color.BLACK;
}
else if (name.equals("Red"))
{
currentColor = Color.RED;
}
else if (name.equals("Blue"))
{
currentColor = Color.BLUE;
}
else if (name.equals("Green"))
{
currentColor = Color.GREEN;
}
else if (name.equals("Orange"))
{
currentColor = Color.ORANGE;
}
}
}
// listener class that listens to the mouse
public class PointListener implements MouseListener, MouseMotionListener {
Graphics g;
public PointListener(Graphics g){
this.g = g;
}
//{
//in case that a user presses using a mouse,
//record the point where it was pressed.
public void mousePressed (MouseEvent event)
{
ptStart = event.getPoint();
}
//mouseReleased method takes the point where a mouse is released,
//using the point and the pressed point to create a line,
//add it to the ArrayList "lineList", and call paintComponent method.
public void mouseReleased (MouseEvent event)
{
ptEnd = event.getPoint();
Line line = new Line(ptStart.x,ptStart.y,ptEnd.x,ptEnd.y,currentColor);
lineList.add(line);
repaint();
}
public void mouseClicked (MouseEvent event) {}
public void mouseEntered (MouseEvent event) {}
public void mouseExited (MouseEvent event) {}
//mouseDragged method takes the point where a mouse is dragged
//and call paintComponent method
public void mouseDragged(MouseEvent event)
{
ptDrag = event.getPoint();
Line dragLine = new Line(ptStart.x,ptStart.y,ptDrag.x,ptDrag.y,currentColor);
dragLine.draw(g);
repaint();
}
public void mouseMoved(MouseEvent event) {}
} // end of PointListener
} // end of Whole Panel Class
这是我的Line课程 import java.awt。*;
public class Line {
private int x1,x2,y1,y2;
private Color color;
public Line(int px1, int py1, int px2, int py2, Color pColor) // constructor that sets the color of the line as well as the coordinates
{
x1 = px1;
y1 = py1;
x2 = px2;
y2 = py2;
color = pColor;
}
public void draw(Graphics page)
{
page.setColor(color);// insert user color
page.drawLine(x1, y1, x2, y2);
}
}
答案 0 :(得分：0)
您可以为Graphics添加PointListener变量和构造函数，例如
public class PointListener implements MouseListener, MouseMotionListener {
Graphics g;
//declare point variables
Point ptStart, ptEnd, ptDrag;
public PointListener(Graphics g){
this.g = g;
}
}
编辑：通过这种方式声明您的积分，您可以将它们（特别是ptStart）显示为mouseReleased和mouseDragged
这样您就可以更轻松地在mouseDragged中绘制线条了，因为您可以使用
g.drawLine(ptStart.x, ptStart.y, ptDrag.x, ptDrag.y, currentColor);
然后，当您添加点侦听器时，您只需将代码更改为
//added PointListener object because you previously
//created new object for each statement
//meaning separate objects are listening for Mouse and MouseMotion
PointListener pl = new PointListener(canvas.getGraphics());
//this should work but one way or another
//you need to pass the Graphics object
canvas.addMouseListener(pl);
canvas.addMouseMotionListener(pl);