在另一个函数中声明的画布上绘制java

Question

我有一个应用程序，它有一个swing用户界面类，它有一些按钮，可以将变量发送到canvas类，就像这样

public class createWindow extends JFrame implements ActionListener
{
    createCanvas canvas = new createCanvas(10, 10);
    JPanel mainPanel = new JPanel();
    public createWindow()
    {
        mainPanel.add(canvas, BorderLayout.CENTER);
    }
}

createCanvas是一个声明paintComponent的类

public class createCanvas extends JPanel
{
    int xValue;
    int yValue;
    int xCoordinate;
    int yCoordinate;

    public createCanvas(int x, int y)
    {
        xValue = x;
        yValue = y;
    }

    public void setXCoordinate(int x)
    {
        xCoordinate = x;
    }

    public void setYCoordinate(int y)
    {
        yCoordinate = y;
    }

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        drawGrid(g, this.xValue, this.yValue);
        g.fillArc(xCoordinate, yCoordinate, 6, 6, 0, 360);
    }

    public drawGrid(Graphics g, int xLength, int yLength)
    {
        //creates a grid that is xLength x yLength
    }
}

然而，我也有一个选择的对象，我想有一个。函数，该函数可以在createCanvas中使用paintComponent。 当然，问题是，当我需要在网格上绘制节点时，我可以设置坐标，但是如何在createWindow中声明的画布上显示节点

public class Node()
{
    int xCoordinate;
    int yCoordinate;

    //Suitable constructors, sets, gets
    public void draw()
    {
        createCanvas canvas = new createCanvas();
        canvas.setXCoordinate(this.xCoordinate);
        canvas.setYCoordinate(this.yCoordinate);
        canvas.repaint();
    }
}

因此，我想知道是否有一种方法可以让我在createWindow中保存画布上绘制的内容，以及在Object类中绘制的内容

谢谢

Answer 1

您要做的是让对象中的draw方法接受一个Graphics参数。这个Graphics对象将与paintComponent方法中的Graphics上下文相同。可以在JPanel类中创建对象。像这样的

public class Circle {
    int x, y;

    public Circle(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public void drawCirlce(Graphics g) {
        g.fillRect(x, y, 50, 50);
    }
}

然后在你的JPanel课上

public class CirclePanel extends JPanel {
    Circle circle = new Circle(100, 100);

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        circle.drawCircle(g);
    }
}

您可以在Circle类中为x和y设置一个setter。你应该在JPanel类的某个地方更改它们，然后调用repaint()。你可以按一个键来移动它，也可以用java.util.Timer来设置动画。比如

用Timer

public class CirclePanel extends JPanel {
    Circle circle = new Circle(100, 100);

    public CirclePanel() {
        Timer timer = new Timer(50, new ActionListener(){
            @Override
            public void actionPerfomed(ActionEvent e) {
                circle.x += 10;
                repaint();
            }
        });
        timer.start();
    }

    @Override
    protected void paintComponent(Graphics g) {
       super.paintComponent(g);
       circle.drawCircle(g);
    }
}

用key binding

public class CirclePanel extends JPanel {
    Circle circle = new Circle(100, 100);

    public CirclePanel() {
        InputMap inputMap = getInputMap(JComponent.WHEN_FOCUSED_IN_WINDOW);
        inputMap.put(KeyStroke.getKeyStroke("RIGHT"), "moveRight");
        getActionMap().put("moveRight", new AbstractAction(){
            public void actionPerformed(ActionEvent e) {
                circle.x += 10;
                repaint();
            } 
        });
    }

    @Override
    protected void paintComponent(Graphics g) {
       super.paintComponent(g);
       circle.drawCircle(g);
    }
}

用button press

public class CirclePanel extends JPanel {
    Circle circle = new Circle(100, 100);

    public CirclePanel() {
        JButton button = new JButton("Move Right");
        button.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e) {
                circle.x += 10;
                repaint();
            } 
        });
    }

    @Override
    protected void paintComponent(Graphics g) {
       super.paintComponent(g);
       circle.drawCircle(g);
    }
}