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我正在尝试使用鼠标单击后出现的可拖动十字创建 JPanel。一切正常，但是当我调整 JPanel 的大小时，十字架消失了。我试图在我的 JPanel 中覆盖 paintComponent 方法，但是所有的十字都在坐标 (0,0) 处。我该如何解决？

import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionAdapter;
import java.util.ArrayList;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class CrossPanel extends JPanel implements MouseListener {

private int orderOfCross = 0;
private ArrayList<Cross> crosses;
private int defaultSizeOfCrosses = 10;

CrossPanel() {
    setOpaque(false);
    addMouseListener(this);
    crosses = new ArrayList<Cross>();
}

@Override
public void mouseClicked(MouseEvent e) {
    int x = e.getX();
    int y = e.getY();
    Cross cross = new Cross(orderOfCross++, defaultSizeOfCrosses);
    crosses.add(cross);
    cross.setLocation(x - defaultSizeOfCrosses, y - defaultSizeOfCrosses);
    add(cross);
    repaint();
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    //        for (int i = 0; i < crosses.size(); i++) {
    //            crosses.get(i).paint(g);
    //        }
}

@Override
public void mousePressed(MouseEvent e) {}

@Override
public void mouseReleased(MouseEvent e) {}

@Override
public void mouseEntered(MouseEvent e) {}

@Override
public void mouseExited(MouseEvent e) {}

public static void main(String[] args) {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    CrossPanel crossPane = new CrossPanel();
    f.getContentPane().add(crossPane);
    f.setSize(600, 500);
    f.setLocation(200, 200);
    f.setVisible(true);
}
}

class Cross extends JComponent {

private int order;
protected Cursor draggingCursor = Cursor.getPredefinedCursor(Cursor.HAND_CURSOR);
private volatile int draggedAtX, draggedAtY;
int size;

public Cross(int order, int size) {
    this.order = order;
    this.size = size;
    this.setBounds(0, 0, 4 * size, 3 * size + 10);
    addDragListeners();
    setCursor(draggingCursor);
}

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g;
    g2.setColor(Color.red);
    g2.setStroke(new BasicStroke(3));
    g2.drawLine(0, size, size + size, size);
    g2.drawLine(size, 0, size, size + size);
    Font f = new Font("Monospaced", Font.BOLD, size + 10);
    g2.setFont(f);
    g2.drawString(String.valueOf(order), size - size / 2, 3 * size + 10);
}

private void addDragListeners() {
    addMouseListener(new MouseAdapter() {
        @Override
        public void mousePressed(MouseEvent e) {
            draggedAtX = e.getX();
            draggedAtY = e.getY();
        }
    });
  addMouseMotionListener(new MouseMotionAdapter() {
        @Override
        public void mouseDragged(MouseEvent e) {
            Point newLocation = new Point(e.getX() - draggedAtX + getLocation().x,  e.getY() - draggedAtY + getLocation().y);
            setLocation(newLocation);
        }
    });
}
}
4

1 回答 1

6

我很少看到null布局的用途，对于所有感知的好处，有很多缺点。

整个 Swing API 是围绕布局管理器的使用而设计的，所以你会很疯狂（恕我直言）简单地扔掉所有这些工作。

如果您发现自己处于可用布局管理器似乎无法执行您想要的操作的位置，那么编写您自己的布局管理器可能更值得。

在这里，我提出了一个PropertionalLayoutManager其意图是提供布局功能，该功能将根据父组件的宽度/高度百分比将组件放置在容器上。这意味着，当父组件调整大小时，子组件将以父组件的百分比重新定位。

在此处输入图像描述在此处输入图像描述

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Cursor;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.LayoutManager2;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionAdapter;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class CrossPanel extends JPanel implements MouseListener {

    private int orderOfCross = 0;
    private ArrayList<Cross> crosses;
    private int defaultSizeOfCrosses = 10;

    CrossPanel() {
        setOpaque(false);
        addMouseListener(this);
        crosses = new ArrayList<Cross>();
        setLayout(new PropertionalLayoutManager());
    }

    @Override
    public void mouseClicked(MouseEvent e) {
        int x = e.getX();
        int y = e.getY();
        Cross cross = new Cross(orderOfCross++, defaultSizeOfCrosses);

        float xPos = (float)x / (float)getWidth();
        float yPos = (float)y / (float)getHeight();

        crosses.add(cross);

        add(cross, new PropertionalConstraints(xPos, yPos));
        revalidate();
    }

    public static String format(float value) {
        return NumberFormat.getNumberInstance().format(value);
    }

    @Override
    public void mousePressed(MouseEvent e) {
    }

    @Override
    public void mouseReleased(MouseEvent e) {
    }

    @Override
    public void mouseEntered(MouseEvent e) {
    }

    @Override
    public void mouseExited(MouseEvent e) {
    }

    public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        CrossPanel crossPane = new CrossPanel();
        f.getContentPane().add(crossPane);
        f.setSize(600, 500);
        f.setLocation(200, 200);
        f.setVisible(true);
    }

    public class Cross extends JComponent {

        private int order;
        protected Cursor draggingCursor = Cursor.getPredefinedCursor(Cursor.HAND_CURSOR);
        private volatile int draggedAtX, draggedAtY;
        int size;

        public Cross(int order, int size) {
            this.order = order;
            this.size = size;
//            this.setBounds(0, 0, 4 * size, 3 * size + 10);
            addDragListeners();
            setCursor(draggingCursor);
            Font f = new Font("Monospaced", Font.BOLD, size + 10);
            setFont(f);

        }

        @Override
        public Dimension getPreferredSize() {
            // This is dangrous, you are making assumptions about platforms
            // that you have no eviednce to support.
            FontMetrics fm = getFontMetrics(getFont());
            return new Dimension(Math.max(fm.stringWidth(String.valueOf(order)), size), size + fm.getHeight());
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g;
            g2.setColor(Color.red);
            g2.setStroke(new BasicStroke(3));

            FontMetrics fm = g2.getFontMetrics();

            int width = getWidth() - 1;
            int height = getHeight() - 1;

            int x = (width - fm.stringWidth(String.valueOf(order))) / 2;
            int y = fm.getAscent();
            g2.drawString(String.valueOf(order), x, y);

            int crossSize = Math.min(width, height - fm.getHeight());
            x = (width - crossSize) / 2;
            y = fm.getHeight();
            g2.drawLine(x, y, x + crossSize, y + crossSize);
            g2.drawLine(x + crossSize, y, x, y + crossSize);
        }

        private void addDragListeners() {
            addMouseListener(new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    draggedAtX = e.getX();
                    draggedAtY = e.getY();
                }

            });
            addMouseMotionListener(new MouseMotionAdapter() {
                @Override
                public void mouseDragged(MouseEvent e) {
                    Point newLocation = new Point(e.getX() - draggedAtX + getLocation().x, e.getY() - draggedAtY + getLocation().y);
                    setLocation(newLocation);
                }

            });
        }

    }

    public class PropertionalConstraints {

        private float x;
        private float y;

        public PropertionalConstraints(float x, float y) {
            this.x = x;
            this.y = y;
        }

        public float getX() {
            return x;
        }

        public float getY() {
            return y;
        }

        public void setX(float x) {
            if (x > 1f) {
                x = 1f;
            } else if (x < -0f) {
                x = 0f;
            }
            this.x = x;
        }

        public void setY(float y) {
            if (y > 1f) {
                y = 1f;
            } else if (y < -0f) {
                y = 0f;
            }
            this.y = y;
        }

    }

    public class PropertionalLayoutManager implements LayoutManager2 {

        private Map<Component, PropertionalConstraints> mapConstraints;

        public PropertionalLayoutManager() {
            mapConstraints = new HashMap<>(25);
        }

        public PropertionalConstraints getConstraintsFor(Component comp) {
            return mapConstraints.get(comp);
        }

        public void setConstraintsFor(Component comp, PropertionalConstraints pc) {
            mapConstraints.put(comp, pc);
        }

        @Override
        public void addLayoutComponent(Component comp, Object constraints) {
            if (constraints instanceof PropertionalConstraints) {
                mapConstraints.put(comp, (PropertionalConstraints) constraints);
            } else {
                throw new IllegalArgumentException("Constraints must be PropertionalConstraints");
            }
        }

        @Override
        public Dimension maximumLayoutSize(Container target) {
            return preferredLayoutSize(target);
        }

        @Override
        public float getLayoutAlignmentX(Container target) {
            return 0.5f;
        }

        @Override
        public float getLayoutAlignmentY(Container target) {
            return 0.5f;
        }

        @Override
        public void invalidateLayout(Container target) {

        }

        @Override
        public void addLayoutComponent(String name, Component comp) {

        }

        @Override
        public void removeLayoutComponent(Component comp) {
            mapConstraints.remove(comp);
        }

        @Override
        public Dimension preferredLayoutSize(Container parent) {
            return parent.getSize();
        }

        @Override
        public Dimension minimumLayoutSize(Container parent) {
            return preferredLayoutSize(parent);
        }

        @Override
        public void layoutContainer(Container parent) {
            int width = parent.getWidth();
            int height = parent.getHeight();
            for (Component comp : parent.getComponents()) {
                PropertionalConstraints con = mapConstraints.get(comp);
                if (con != null) {
                    int x = (int)(width * con.getX());
                    int y = (int)(height * con.getY());
                    comp.setSize(comp.getPreferredSize());
                    comp.setLocation(x, y);
                } else {
                    comp.setBounds(0, 0, 0, 0);
                }
            }
        }

    }

}

在一些旁注中，您正在使用“魔术”数字来确定某些元素的大小和渲染位置。这是一个非常糟糕的主意。您应该，尤其是在绘画或印刷时，将所有这些值都基于经验值。

在此示例中，我已恢复为使用FontMertrics来提供所需的信息，以更准确地计算各种元素的大小和位置。这将允许更好的跨平台支持，因为并非所有字体在所有平台上都呈现相同；）

于 2013-04-05T22:59:44.440 回答