调整JPanel大小后，组件消失

时间：2013-04-05 21:40:55

标签： java swing jpanel paintcomponent

我正在尝试创建具有可拖动十字架的JPanel，这些十字架在鼠标单击后出现。一切正常，但当我调整JPanel的大小时，十字架消失了。我试图覆盖JPanel中的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);
        }
    });
}
}

1 个答案:

答案 0 :(得分：6)

我很少看到null布局的用途，因为所有感知到的好处，只有很多人会退缩。

整个Swing API都是围绕布局管理器的设计而设计的，所以你会疯狂（恕我直言）简单地抛弃所有这些工作。

如果您发现自己处于可用的布局管理器似乎没有按照您的意愿行事的位置，那么编写自己的布局管理器可能更有价值。

在这里，我提出了一个PropertionalLayoutManager，其目的是提供布局功能，将基于父组件的宽度/高度的百分比将组件放置在容器上。这意味着，随着父组件的大小调整，子组件将以父级大小的百分比重新定位。

enter image description here enter image description here 

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);
                }
            }
        }

    }

}

在某些方面，您使用“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。你应该，特别是在绘画或印刷时，将所有这些价值都建立在经验值上。

在此示例中，我已恢复使用FontMertrics提供所需信息，以便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，因为并非所有平台上的所有字体都呈现相同;）

相关问题
最新问题