适用于可调整大小的组件的LayoutManager

Question

前一段时间，我阅读了这篇文章，该文章展示了一种在Swing中实现可调整鼠标大小的组件的方法。

作者使用null的LayoutManager以便进行绝对的组件定位。我知道不应该使用null布局，所以我的问题是：

是否有已经实现的LayoutManager允许组件的绝对定位，还是我必须自己实现它？

Answer 1

布局管理器实际上执行3件事：

1. 设置组件的位置。由于您需要能够拖动组件，因此您不希望布局管理器执行此操作。

2. 设置组件的大小。由于您需要能够调整组件的大小，因此您不希望这样做。但是，您可能要根据组件的首选大小为组件指定默认大小。这样，您无需在创建组件时指定大小。

3. 根据添加到其上的组件确定父面板的首选大小。这将允许滚动窗格正常运行，因为可以根据需要添加/删除滚动条。因此，您需要确定拖动方式的行为。也就是说，允许您将组件拖动到面板的当前边界之外。如果是这样，面板的首选大小应自动增加。

是否有任何已实现的LayoutManager允许组件的绝对定位

我一直在与接近您需求的布局管理器一起玩耍。它被设计为可与Moving Windows垃圾桶提供的链接中的ComponentMover类一起使用。

这是我针对此类的测试代码：

import java.awt.*;
import javax.swing.*;
import javax.swing.border.*;

/**
 */
public class DragLayout implements LayoutManager, java.io.Serializable
{
    public DragLayout()
    {
    }

    /**
     * Adds the specified component with the specified name to the layout.
     * @param name the name of the component
     * @param comp the component to be added
     */
    @Override
    public void addLayoutComponent(String name, Component comp) {}


    /**
     * Removes the specified component from the layout.
     *
     * @param comp the component to be removed
     */
    @Override
    public void removeLayoutComponent(Component component)
    {
    }

    /**
     *  Determine the minimum size on the Container
     *
     *  @param   target   the container in which to do the layout
     *  @return  the minimum dimensions needed to lay out the
     *           subcomponents of the specified container
     */
    @Override
    public Dimension minimumLayoutSize(Container parent)
    {
        synchronized (parent.getTreeLock())
        {
            return preferredLayoutSize(parent);
        }
    }

    /**
     *  Determine the preferred size on the Container
     *
     *  @param   parent   the container in which to do the layout
     *  @return  the preferred dimensions to lay out the
     *           subcomponents of the specified container
     */
    @Override
    public Dimension preferredLayoutSize(Container parent)
    {
        synchronized (parent.getTreeLock())
        {
            return getLayoutSize(parent);
        }
    }

    /*
     *  The calculation for minimum/preferred size it the same. The only
     *  difference is the need to use the minimum or preferred size of the
     *  component in the calculation.
     *
     *  @param   parent  the container in which to do the layout
     */
    private Dimension getLayoutSize(Container parent)
    {
        Insets parentInsets = parent.getInsets();
        int x = parentInsets.left;
        int y = parentInsets.top;
        int width = 0;
        int height = 0;

        //  Get extreme values of the components on the container

        for (Component component: parent.getComponents())
        {
            if (component.isVisible())
            {
                Point p = component.getLocation();
                Dimension d = component.getPreferredSize();
                x = Math.min(x, p.x);
                y = Math.min(y, p.y);
                width = Math.max(width, p.x + d.width);
                height = Math.max(height, p.y + d.height);
            }
        }

        // Width/Height is adjusted if any component is outside left/top edge

        if (x < parentInsets.left)
            width += parentInsets.left - x;

        if (y < parentInsets.top)
            height += parentInsets.top - y;

        //  Adjust for insets

        width += parentInsets.right;
        height += parentInsets.bottom;
        Dimension d = new Dimension(width, height);

        return d;
//      return new Dimension(width, height);
    }

    /**
     * Lays out the specified container using this layout.
     *
     * @param     target   the container in which to do the layout
     */
    @Override
    public void layoutContainer(Container parent)
    {
    synchronized (parent.getTreeLock())
    {
        Insets parentInsets = parent.getInsets();

        int x = parentInsets.left;
        int y = parentInsets.top;

        //  Get X/Y location outside the bounds of the panel

        for (Component component: parent.getComponents())
        {
            if (component.isVisible())
            {
                Point location = component.getLocation();
                x = Math.min(x, location.x);
                y = Math.min(y, location.y);
            }
        }

        x = (x < parentInsets.left) ? parentInsets.left - x : 0;
        y = (y < parentInsets.top) ? parentInsets.top - y : 0;

        //  Set bounds of each component

        for (Component component: parent.getComponents())
        {
            if (component.isVisible())
            {
                Point p = component.getLocation();
                Dimension d = component.getPreferredSize();

                component.setBounds(p.x + x, p.y + y, d.width, d.height);
            }
        }
    }}

    /**
     * Returns the string representation of this column layout's values.
     * @return   a string representation of this layout
     */
    public String toString()
    {
        return "["
            + getClass().getName()
            + "]";
    }

    public static void main( String[] args )
    {
        ComponentMover cm = new ComponentMover();
        cm.setEdgeInsets( new Insets(-100, -100, -100, -100) );
//      cm.setEdgeInsets( new Insets(10, 10, 10, 10) );
        cm.setAutoLayout(true);

        JPanel panel = new JPanel( new DragLayout() );
        panel.setBorder( new MatteBorder(10, 10, 10, 10, Color.YELLOW) );

        createLabel(cm, panel, "North", 150, 0);
        createLabel(cm, panel, "West", 0, 100);
        createLabel(cm, panel, "East", 300, 100);
        createLabel(cm, panel, "South", 150, 200);
        createLabel(cm, panel, "Center", 150, 100);

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add( new JScrollPane(panel) );
        frame.pack();
        frame.setLocationRelativeTo( null );
        frame.setVisible( true );
    }

    public static void createLabel(ComponentMover cm, JPanel panel, String text, int x, int y)
    {
        JLabel label = new JLabel( text );
        label.setOpaque(true);
        label.setBackground( Color.ORANGE );
        label.setLocation(x, y);
        panel.add( label );
        cm.registerComponent( label );
    }

}

1. 对于此布局，始终假定大小为首选大小。您将需要更改此设置。大小为（0，0）时，可以将大小设置为首选大小。在确定父容器的首选大小时，您还需要使用组件的大小（而不是首选大小）。

2. 可以配置ComponentMover类，以允许您将组件拖动到父容器的边界之外，或者将组件保持在边界之内。如果允许将组件移出边界，则将自动调整首选大小，以考虑组件的新位置。

3. 如果将组件拖动到顶部或左侧边界之外，则所有组件都将移动（向右或向下），请确保没有组件位于负位置。