我正在尝试创建应用程序，用户可以在Canvas中绘制线条。用户可以从下拉列表中选择方向并输入行长。第一行从Canvas中心开始，下一行从前一个结束开始，依此类推 - 用户可以逐个绘制多行，并且所有行都是连接的。
我有两个类 - TurtleApplet用程序逻辑创建GUI和Canvas：
public class TurtleApplet extends JApplet implements ActionListener
{
private JComboBox direction;
private JRadioButton activeButton, passiveButton;
private Button drawButton;
private ButtonGroup group;
private TextField pixels;
private Canvas canvas;
private JPanel panel;
private JPanel panelRadio;
private Button quitPr;
public void init()
{
//directions
String[] directionStrings = { "Right", "Left", "Up", "Down"};
direction = new JComboBox(directionStrings);
//direction.setSelectedIndex(4);
//Buttons
activeButton = new JRadioButton("Aktīvs");
passiveButton = new JRadioButton("Neaktīvs");
quitPr = new Button("Iziet");
//Canvas
canvas = new Canvas();
//canvas.setSize(600, 500);
//canvas.setBackground(Color.red);
canvas.setBorder(BorderFactory.createTitledBorder("Turtle drawing"));
//Panels
panel = new JPanel();
panelRadio =new JPanel();
panel.setLayout(new FlowLayout());
panelRadio.setLayout(new FlowLayout());
//actionListener
activeButton.addActionListener(this);
passiveButton.addActionListener(this);
activeButton.setSelected(true);
quitPr.addActionListener(this);
//Add radiobuttons
group = new ButtonGroup();
group.add(activeButton);
group.add(passiveButton);
//Add Buttons to panel
panelRadio.add(activeButton);
panelRadio.add(passiveButton);
//textfield
pixels = new TextField(12);
//Draw button
drawButton = new Button("Zīmēt");
drawButton.addActionListener(this);
direction.addActionListener(this);
panel.add(panelRadio);
panel.add(pixels);
panel.add(direction);
panel.add(drawButton);
panel.add(quitPr);
getContentPane().add(panel,"North");
getContentPane().add(canvas, "Center");
setSize(650,550);
}
public void actionPerformed( ActionEvent e)
{
if ( e.getSource() == activeButton ) {
drawButton.setVisible(true);
pixels.setEditable(true);
} else if (e.getSource() == passiveButton) {
drawButton.setVisible(false);
pixels.setEditable(false);
} else if(e.getSource() == quitPr){
System.exit(0);
}else if(e.getSource() == drawButton){
int y = Integer.parseInt(pixels.getText());
canvas.addPatt(direction.getSelectedIndex(), Integer.parseInt(pixels.getText()));
repaint();
}
//repaint();
}
}
public class Canvas extends JPanel {
private static final int RIGHT=0, LEFT=1, UP=2, DOWN=3;
public static final int WIDTH=600, HEIGHT=500;
private int direction = 0 ;
private int pixels;
//rivate List points;
public Polygon t = new Polygon();
//public Dimension d = getSize();
public int x = WIDTH/2;
public int y = HEIGHT/2;
public Canvas() {
setSize(WIDTH, HEIGHT);
}
public void addPatt(int pat, int lev) {
direction = pat;
pixels = lev;
}
public void paintComponent(Graphics g) {
switch (direction) {
case LEFT:
drawLineLeft(g, pixels);
break;
case RIGHT:
drawLineRight(g, pixels);
break;
case UP:
drawLineUp(g, pixels);
break;
case DOWN:
drawLineDown(g, pixels);
break;
}
}
private void drawLineLeft(Graphics g, int pix){
if(pix > 0){
g.drawLine(x, y, x-10*pix, y);//left
x =x -10*pix;
}
}
private void drawLineUp(Graphics g, int pix){
if(pix > 0){
g.drawLine(x, y, x, y-10*pix);//up
y = y-10*pix;
}
}
private void drawLineRight(Graphics g, int pix){
if(pix > 0){
g.drawLine(x, y, x+10*pix, y);//right
x = x+10*pix;
}
}
private void drawLineDown(Graphics g, int pix){
if(pix > 0){
g.drawLine(x, y, x, y+10*pix);// down
y = y+10*pix;
}
}
}
Applet有效，但问题是在绘制新的行时保存以前的行。当用户输入行的方向和长度并按下按钮时，屏幕上会出现新行，但前一行会消失。我知道问题出在paintComponent方法，但我不知道如何正确地纠正我的代码以使所有行都可见。我被建议将点坐标存储在数组中，然后通过在paintComponent中循环遍历数组来绘制线条，但我不知道如何实现这一点。也许有更好的解决方案？
答案 0 :(得分：3)
正如我在last question中所说，case状态就像if-else，你只允许它画一条线。您需要维护List个“行”，每次调用paintComponent方法时都可以迭代
因为一行由多个属性表示，所以最好将该信息封装到一个简单的类或POJO中
public enum Direction {
UP, DOWN, LEFT, RIGHT
}
public class Line {
private Direction direction;
private int length;
public Line(Direction direction, int length) {
this.direction = direction;
this.length = length;
}
public Direction getDirection() {
return direction;
}
public int getLength() {
return length;
}
}
在这里，我将方向属性分离为一个简单的enum，这使您可以更轻松地在程序的其他位置引用属性
然后你保持List个Line，当调用paintComponent时，你只需重新迭代并重新绘制......
public class Canvas extends JPanel {
public static final int WIDTH = 600, HEIGHT = 500;
public int x = WIDTH / 2;
public int y = HEIGHT / 2;
private List<Line> lines;
public Canvas() {
lines = new ArrayList<>(25);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(WIDTH, HEIGHT);
}
public void addPatt(Direction direction, int length) {
lines.add(new Line(direction, length));
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
for (Line line : lines) {
switch (line.getDirection()) {
case UP:
drawLineUp(g, line.getLength());
break;
case DOWN:
drawLineDown(g, line.getLength());
break;
case LEFT:
drawLineLeft(g, line.getLength());
break;
case RIGHT:
drawLineDown(g, line.getLength());
break;
}
}
}
private void drawLineLeft(Graphics g, int pix) {
if (pix > 0) {
g.drawLine(x, y, x - 10 * pix, y);//left
x = x - 10 * pix;
}
}
private void drawLineUp(Graphics g, int pix) {
if (pix > 0) {
g.drawLine(x, y, x, y - 10 * pix);//up
y = y - 10 * pix;
}
}
private void drawLineRight(Graphics g, int pix) {
if (pix > 0) {
g.drawLine(x, y, x + 10 * pix, y);//right
x = x + 10 * pix;
}
}
private void drawLineDown(Graphics g, int pix) {
if (pix > 0) {
g.drawLine(x, y, x, y + 10 * pix);// down
y = y + 10 * pix;
}
}
}
请记住，在Swing中绘画具有破坏性，每次调用paintComponent时，都需要重新绘制组件的整个状态。
有关绘画如何运作的详细信息，请参阅Painting in AWT and Swing和Performing Custom Painting
答案 1 :(得分：0)
我被建议将点坐标存储在数组中，然后通过在paintComponent中循环遍历数组来绘制线条，但我不知道如何实现这一点。
这取决于您的确切要求。
如果您需要添加/删除行的功能，那么这可能是最好的方法。
如果您只需要添加线条的功能，那么您可能希望将线条直接绘制到BufferedImage，然后在JLabel上将BufferedImage显示为图标。
查看Custom Painting Approaches，比较两种方法，并提供两种方法的工作示例。