如何在JPanel中使用RectangularShape繪制JPanel

Question

我在繪制RectangularShapes或Shapes時遇到問題。 我需要在實際的Panel中而不是在Frame中，因為我需要這種靈活性。 但我一直陷入困境。 我沒有接受任何語言的GUI培訓，因此非常感謝您的反饋。

代碼如下，請幫助我找出為什么這不起作用，以及我如何讓它工作。

public class GUI_Test 
{
    public static void main(String[] args)
    {
        GUI_Test gui = new GUI_Test();
        gui.tryBasic();
    }


    public void tryBasic()
    {
        JFrame MyFrame = new JFrame();
        MyFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        MyFrame.setSize(800, 500);
        MyFrame.setLayout(new BorderLayout());

        // This won't work and can't figure out why!!!!
        // The button appears but not the Ellipse.
        JPanel JP = new JPanel();
        JButton btn3 = new JButton("This is a button");
        JP.add(new MyGUIObject(new Ellipse2D.Double(70, 70, 100, 100), Color.red));
        JP.add(btn3);
        MyFrame.getContentPane().add(JP);

        // This works but I need it in a panel for easier control 
        //MyFrame.add(new MyGUIObject(new Ellipse2D.Double(70, 70, 100, 100), Color.blue));

        // This of course works.
        //MyFrame.getContentPane().add(new MyGUIObject(new Ellipse2D.Double(70, 70, 100, 100), Color.green));

        MyFrame.setVisible(true);

    }
    public class MyGUIObject extends JPanel
    {
        protected RectangularShape RecObj;
        protected Color myColor;    
        public MyGUIObject(RectangularShape SetShape, Color setColor)
        {
            RecObj = SetShape;
            myColor = setColor;
        }
        @Override
        protected void paintComponent(Graphics g)
        {
            Graphics2D g2d = (Graphics2D) g;
            g2d.setPaint(myColor);
            g2d.fill(RecObj);
        }
    }
}

Answer 1

我可以看到三個主要問題。

1. 你不是從paintComponent方法調用super.paintComponent ，這會引起一些有趣但令人討厭的油漆文物
2. 默認情況下， JPanel使用FlowLayout ， JFrame使用BorderLayout ，這進一步復雜化......
3. 您沒有為MyGUIObject類提供任何大小調整提示，因此FlowLayout將使用JPanel的默認preferredSize ，它在計算JPanel的布局時為0x0 。

首先，從paintComponent方法調用super.paintComponent並覆蓋getPreferredSize方法

public class MyGUIObject extends JPanel {

    protected RectangularShape RecObj;
    protected Color myColor;

    public MyGUIObject(RectangularShape SetShape, Color setColor) {
        RecObj = SetShape;
        myColor = setColor;
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(400, 400);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setPaint(myColor);
        g2d.fill(RecObj);
    }
}

接下來，將JPanel使用的布局更改為BorderLayout （雖然默認的FlowLayout可以使用，但BorderLayout會給你一點控制）

JPanel JP = new JPanel(new BorderLayout());
JButton btn3 = new JButton("This is a button");
JP.add(new MyGUIObject(new Ellipse2D.Double(70, 70, 100, 100), Color.red));
JP.add(btn3, BorderLayout.SOUTH);
MyFrame.getContentPane().add(JP);

看看AWT和Swing中的 繪畫 ， 執行自定義繪畫 ， 在容器中布置組件以及如何使用邊框以獲取更多詳細信息

Answer 2

這個怎么樣：

public class GUI_Test {
    public static void main(String[] args) {
        GUI_Test gui = new GUI_Test();
        gui.tryBasic();
    }

    public void tryBasic() {
        JFrame frame = createFrame();
        JPanel panel = new JPanel(new BorderLayout());
        JButton button = new JButton("This is a button");
        JPanel buttonPanel = new JPanel(new FlowLayout());
        buttonPanel.add(button);
        MyGUIObject guiObject = new MyGUIObject(new Ellipse2D.Double(70, 70, 100, 100), Color.red);
        panel.add(buttonPanel, BorderLayout.PAGE_START);
        panel.add(guiObject,BorderLayout.CENTER);
        frame.getContentPane().add(panel, BorderLayout.CENTER);
        frame.setVisible(true);
    }

    private JFrame createFrame() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(800, 500);
        frame.setLayout(new BorderLayout());
        return frame;
    }

    public class MyGUIObject extends JPanel {
        protected RectangularShape RecObj;
        protected Color myColor;

        public MyGUIObject(RectangularShape SetShape, Color setColor) {
            RecObj = SetShape;
            myColor = setColor;
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g;
            g2d.setPaint(myColor);
            g2d.fill(RecObj);
        }
    }
}