java - 无换行符和/或垂直方向的 FlowLayout

Question

这是 this question 的后续内容。任何可行的答案也将回答这个问题。

哪种布局可以使用尽可能少的修改来复制 FlowLayout 的对齐性质，但永远不会换行，并且也可以从上到下的方式使用？

明显的候选者，BoxLayout ，与 JPanel 不能很好地配合。考虑以下两个示例:

import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

class App
{
  public static void main(String[] args)
  {
    JFrame window = new JFrame();
    Box box = new Box(BoxLayout.Y_AXIS);
    for(int i = 0; i < 5; ++i)
    {
      JLabel label = new JLabel("XX");
      box.add(label);
    }
    box.add(Box.createVerticalGlue());
    window.add(box);
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setVisible(true);
  }
}

这将正确显示一条垂直的标签线，从顶部开始，随着标签占用的空间而向底部延伸。很好。

但是，只需稍微修改一下即可:

  public static void main(String[] args)
  {
    JFrame window = new JFrame();
    Box box = new Box(BoxLayout.Y_AXIS);
    for(int i = 0; i < 5; ++i)
    {
      JLabel label = new JLabel("XX");
      JPanel panel = new JPanel();
      panel.add(label);
      box.add(panel);
    }
    box.add(Box.createVerticalGlue());
    window.add(box);
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setVisible(true);
  }

这会将 Box 的所有组件拉伸(stretch)到相同的高度，使标签彼此远离。不好。

重写 JPanel 的 getPreferredSize 和 getMaximumSize 方法(使用 getMinimumSize)没有效果，并且是一个不好的修复方法，因为它依赖于组件而不是容器及其布局。

<小时/>

附录:
这是使用 GroupLayout 的一次非常成功的尝试。不幸的是，设计者似乎没有想到，在 DEFAULT_SIZE 和 PREFERRED_SIZE 中选择 MINIMUM_SIZE 会是一个好主意。

此外，如果可以反转 GroupLayout.SequentialGroup 的顺序，则 API 无法帮助弄清楚如何反转。我当然不知道如何扩展该类。

import java.awt.Component;
import java.awt.ComponentOrientation;
import java.awt.Container;
import javax.swing.GroupLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

class LineLayout extends GroupLayout
{
  public LineLayout(Container owner, int axis)
  {
    super(owner);
    this.direction = axis;
    this.direction |= owner.getComponentOrientation() != ComponentOrientation.LEFT_TO_RIGHT
                    ? LineLayout.RIGHT_TO_LEFT : LineLayout.LEFT_TO_RIGHT;
    this.setupGroups();
  }
  public LineLayout(Container owner, int axis, int orientation)
  {
    super(owner);
    this.direction = axis;
    this.direction |= orientation;
    this.setupGroups();
  }

  @Override // to replicate FlowLayout functionality : this method is called from owner.add
  public void addLayoutComponent(Component component, Object constraints)
  {
    if(constraints == null)
    {
      // REALLY surprised that this works, considering that overriding the JPanel's
      // getMaximumSize method with getPreferredSize had no effect
      this.horizontal.addComponent(component, GroupLayout.DEFAULT_SIZE,
                                              GroupLayout.DEFAULT_SIZE,
                                              GroupLayout.PREFERRED_SIZE);
      this.vertical.addComponent  (component, GroupLayout.DEFAULT_SIZE,
                                              GroupLayout.DEFAULT_SIZE,
                                              GroupLayout.PREFERRED_SIZE);
    }
    // TODO: else
  }

  protected void setupGroups()
  {
    super.setAutoCreateGaps(false); // does nothing
    if((this.direction & LineLayout.AXIS) == LineLayout.Y_AXIS)
    {
      this.horizontal = super.createParallelGroup();
      this.vertical   = (this.direction & LineLayout.ORIENTATION) == LineLayout.RIGHT_TO_LEFT
                      ? this.createSequentialInvertedGroup() : super.createSequentialGroup();
    }
    else
    {
      this.horizontal = (this.direction & LineLayout.ORIENTATION) == LineLayout.RIGHT_TO_LEFT
                      ? this.createSequentialInvertedGroup() : super.createSequentialGroup();
      this.vertical   = super.createParallelGroup();
    }
    super.setHorizontalGroup(this.horizontal);
    super.setVerticalGroup  (this.vertical);
  }

  // How!?
  // protected LineLayout.SequentialInvertedGroup createSequentialInvertedGroup() { return new LineLayout.SequentialInvertedGroup(); }
  protected GroupLayout.SequentialGroup createSequentialInvertedGroup() { return super.createSequentialGroup(); } // placeholder

  protected int direction;
  protected GroupLayout.Group horizontal;
  protected GroupLayout.Group vertical;

  // not sure how reliable the constant field values of BoxLayout are, whether it's smart to assume them unchanging over the ages
  public static final int AXIS = 0b1;
  public static final int X_AXIS = 0b0; // = BoxLayout.X_AXIS;
  public static final int Y_AXIS = 0b1; // = BoxLayout.Y_AXIS;
  public static final int ORIENTATION = 0b10;
  public static final int LEFT_TO_RIGHT = 0b00; // also top to bottom
  public static final int RIGHT_TO_LEFT = 0b10; // also bottom to top

  // No idea how; only has "add" methods; cannot actually do anything with the added components!?
  //protected static class SequentialInvertedGroup extends GroupLayout.SequentialGroup
  //{}
}

class Applikation
{
  public static void main(String[] args)
  {
    JFrame window = new JFrame();
    JPanel box = new JPanel();
    box.setLayout(new LineLayout(box, LineLayout.Y_AXIS));
    for(int i = 0; i < 5; ++i)
    {
      JLabel label = new JLabel("XX");
      JPanel panel = new JPanel();
      panel.add(label);
      box.add(panel);
    }
    window.add(box);
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setVisible(true);
  }
}

如果您尝试一下，您会注意到“XX”标签之间仍然存在明显的边框空间，每个间隙大约占据额外标签的 2/3。虽然已经比 BoxLayout 示例好得多，但我认为没有什么好方法可以进一步改善此间距。

Answer 1

private static int MAX_HEIGHT = 40;
private static final Dimension DIMENSION = new Dimension(Integer.MAX_VALUE, MAX_HEIGHT); 
public static void main(String[] args)
{
JFrame window = new JFrame();
Box box = new Box(BoxLayout.Y_AXIS){
    private static final long serialVersionUID = 1L;

    @Override
    public Component add(Component comp) {
        comp.setMaximumSize(DIMENSION);
        return super.add(comp);
    }
};
for(int i = 0; i < 5; ++i)
{
  JLabel label = new JLabel("XX");
  JPanel panel = new JPanel();
  panel.add(label);
  box.add(panel);
}
window.add(box);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.pack();
window.setVisible(true);
}