组件调整的JPanel后消失(Components disappear after resizing

2019-08-19 23:46发布

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我试图用鼠标点击之后出现十字拖动创建的JPanel。 一切工作正常，但是当我调整JPanel的交叉盘消失。 我试图覆盖paintComponent方法在我的JPanel但随后交叉盘在坐标（0,0）。 我怎样才能解决这个问题？ 

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);
        }
    });
}
}

Answer 1:

我很少看到了一个使用null布局，为所有的预期收益，实在有很多抽奖背上。

在整个挥杆API的设计围绕着利用布局管理器，所以你一定是疯了（恕我直言），以简单地抛出所有这些工作了。

如果你在一个位置，可用的布局管理器似乎并不做你想做的发现自己，这可能是更值得写你自己的。

在这里，我介绍一个PropertionalLayoutManager ，其目的是提供将放置基于父组件的宽度/高度的百分比的容器上的组件布局能力。 这意味着，作为父组件的大小时，子组件会在父大小的比例重新定位自己。 

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，您正在使用“魔术”号来确定某些元素的大小和位置呈现。 这是一个非常糟糕的主意。 你应该，绘画或印刷尤其是，立足于经验值，这些值。

在这个例子中，我已经回复到使用FontMertrics以提供所需的信息，以更准确地计算大小和各种元件的位置。 这将允许更好的跨平台支持，因为不是所有的字体呈现在所有平台上相同;）



文章来源: Components disappear after resizing JPanel
标签： java swing jpanel paintcomponent
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