通過使用paintComponent在JApplet中繪制多條連接的線

Question

我試圖創建用戶可以在Canvas中畫線的應用程序。 用戶可以從下拉列表中選擇方向，然后輸入行長。 第一行從Canvas的中心開始，下一條從上一條的結束處開始，依此類推-用戶可以一條一條繪制多條線，並且所有線都已連接。

我有兩個類-TurtleApplet，它使用程序邏輯創建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，但是問題是在繪制新行時保存以前的行。 當用戶輸入行的方向和長度並按下按鈕時，新的行會出現在屏幕上，但是前一行會消失。 我知道問題出在paintComponent方法上，但是我不知道如何准確地糾正我的代碼以使所有行都可見。 建議我將點坐標存儲在數組中，然后通過遍歷paintComponent中的數組來繪制線，但是我不知道該如何實現。 也許有更好的解決方案？

Answer 1

就像我在上一個問題中所說的那樣， case狀態就像if-else ，您只允許它畫一條線。 您需要維護一個“行” List ，每次調用paintComponent方法時都可以對其進行迭代

因為一行由多個屬性表示，所以最好將這些信息封裝到一個簡單的類或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;
    }


}

在這里，我將direction屬性分為一個簡單的enum ，這使您可以在程序中的其他位置更輕松地引用這些屬性

然后，維護一個Line的List ，當調用paintComponent時，您只需重新迭代並重新繪制即可。

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;
        }
    }

}

記住，Swing中的繪制是破壞性的，每次調用paintComponent時， paintComponent重新繪制組件的整個狀態。

有關繪畫工作原理的更多詳細信息，請參見“ AWT中的繪畫”和“搖擺和執行自定義繪畫 ”

Answer 2

建議我將點坐標存儲在數組中，然后通過遍歷paintComponent中的數組來繪制線，但是我不知道該如何實現。

這取決於您的確切要求。

如果您需要添加/刪除行的功能，那么這可能是最好的方法。

如果只需要添加線的功能，則可能需要將線直接繪制到BufferedImage上，然后在JLabel上將BufferedImage顯示為圖標。

查看“ 自定義繪畫方法” ，它比較了兩種方法並提供了這兩種方法的工作示例。