设置 BorderLayout 并调用 PaintComponent()

Question

我的问题：我有一个 RoundedPanel 类，它扩展 JPanel 并重写 paintComponent() 方法，以便在面板周围绘制圆角。我创建了一个扩展 RoundedPanel 的 MyPanel 类。

当我使用 FlowLayout 布局将面板放在 MyPanel 上时，会出现圆形边框。 为了调整面板上组件的大小以使其填充最大空间，我用 Borderlayout 替换了 FlowLayout。但随后，paintComponent() 方法从未被调用，并且圆角边框不再出现。

有谁知道如何创建一个圆形面板，当调整窗口大小时，其组件会被拉伸以填充空间？有人可以解释一下为什么使用 Borderlayout 时不调用 paintComponent() 方法吗？

提前致谢。

代码：

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Demo extends JFrame {

    public static final int WINDOW_WIDTH = 540;
    public static final int WINDOW_HEIGHT = 540;
    private static MyPanel myPanel;

    private Demo() {
        super();
        myPanel = new MyPanel();
        getContentPane().add(myPanel);
        setSize(new Dimension(500, 500));
        setPreferredSize(new Dimension(500, 500));
        setVisible(true);
    }

    public static void main(String[] args) {
        new Demo();
    }
}

class MyPanel extends RoundedPanel {

    private JPanel rootPanel = new JPanel();

    public MyPanel() {
        super();
        rootPanel = buildRootPanel();
        rootPanel.setPreferredSize(new Dimension(400, 400));
        rootPanel.setBackground(Color.RED);
        add(rootPanel);

        // When uncommented, the Textfield is correctly resized to fit all available space , but the rounder border doesnt appear
        //setLayout(new BorderLayout());
        //add(rootPanel, BorderLayout.CENTER);
    }

    private JPanel buildRootPanel() {
        rootPanel.setLayout(new BorderLayout());
        JTextField field = new JTextField();
        rootPanel.add(field, BorderLayout.CENTER);
        return rootPanel;
    }
}

class RoundedPanel extends JPanel {

    protected int strokeSize = 1;//Stroke size. it is recommended to set it to 1 for better view
    private Color strokeColor = Color.BLACK;
    protected Color shadowColor = Color.black;//Color of shadow
    protected boolean shady = true;//  Sets if it drops shadow
    protected boolean highQuality = true;// Sets if it has an High Quality view
    protected Dimension arcs = new Dimension(20, 20);// Double values for Horizontal and Vertical radius of corner arcs
    protected int shadowGap = 5;// Distance between shadow border and opaque panel border
    protected int shadowOffset = 4; // The offset of shadow.
    protected int shadowAlpha = 150;// The transparency value of shadow. ( 0 - 255)

    public RoundedPanel() {
        super();
        setOpaque(false);
    }

    @Override
    protected void paintComponent(Graphics g) {

        System.out.println("++++++++++++++ in paintComponent");
        super.paintComponent(g);
        int width = getWidth();
        int height = getHeight();
        int shadowGap = this.shadowGap;
        Color shadowColorA = new Color(shadowColor.getRed(), shadowColor.getGreen(), shadowColor.getBlue(), shadowAlpha);
        Graphics2D graphics = (Graphics2D) g;

        //Sets antialiasing if HQ.
        if (highQuality) {
            graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        }

        //Draws shadow borders if any.
        if (shady) {
            graphics.setColor(shadowColorA);
            graphics.fillRoundRect(
                shadowOffset,// X position
                shadowOffset,// Y position
                width - strokeSize - shadowOffset, // width
                height - strokeSize - shadowOffset, // height
                arcs.width, arcs.height);// arc Dimension
        } else {
            shadowGap = 1;
        }

        //Draws the rounded opaque panel with borders.
        graphics.setColor(getBackground());
        graphics.fillRoundRect(0, 0, width - shadowGap, height - shadowGap, arcs.width, arcs.height);
        //graphics.setColor(getForeground());
        graphics.setColor(strokeColor);

        graphics.setStroke(new BasicStroke(strokeSize));
        graphics.drawRoundRect(0, 0, width - shadowGap, height - shadowGap, arcs.width, arcs.height);

        //Sets strokes to default, is better.
        graphics.setStroke(new BasicStroke());
    }
}

Answer 1

看起来该字段占据了面板的所有空间。如果子级覆盖了所有父级并且父级不可见，则无需调用paintComponent()，因此不会调用它。
尝试为内容添加空边框。