我很少看到null 布局的用途，对于所有可感知的好处，有很多缺点。
整个 Swing API 都是围绕布局管理器的使用而设计的，所以你会疯了（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的布局管理器似乎无法满足您的需求，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，其目的是提供布局功能，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，子组件将按照父组件的一定百分比重新定位。
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，因为并非所有字体在所有平台上都呈现相同;)