布局管理器（二）

JPanel panel = new JPanel();
LayoutManager layout = new BoxLayout (panel, BoxLayout.X_AXIS);
panel.setLayout(layout);
与所有其他的系统提供的布局管理器不同，BoxLayout与容器是双向绑定在一起的，由管理器到容器同时也由容器到管理。

package swingstudy.ch10;
import java.awt.Component;
import java.awt.Container;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class YAxisAlignX {
private static Container makeIt(String title, float alignment) {
String labels[] = {"--", "----", "------", "--------"};
JPanel container = new JPanel();
container.setBorder(BorderFactory.createTitledBorder(title));
BoxLayout layout = new BoxLayout(container, BoxLayout.Y_AXIS);
container.setLayout(layout);
for(int i=0, n=labels.length; i<n; i++) {
JButton button = new JButton(labels[i]);
button.setAlignmentX(alignment);
container.add(button);
}
return container;
}
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Runnable runner = new Runnable() {
public void run() {
JFrame frame = new JFrame("Alignment Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container panel1 = makeIt("Left", Component.LEFT_ALIGNMENT);
Container panel2 = makeIt("Center", Component.CENTER_ALIGNMENT);
Container panel3 = makeIt("Right", Component.RIGHT_ALIGNMENT);
frame.setLayout(new FlowLayout());
frame.add(panel1);
frame.add(panel2);
frame.add(panel3);
frame.pack();
frame.setVisible(true);
}
};
EventQueue.invokeLater(runner);
}
}
当所有组件具有相同的垂直对齐时，x坐标的BoxLayout的作用类似。组件将会显示在容器的顶部，中部或是底，而不是左对齐，中间对齐或是右对齐调整。图10-10显示了这种外观。

package swingstudy.ch10;
import java.awt.Component;
import java.awt.Container;
import java.awt.EventQueue;
import java.awt.GridLayout;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class XAxisAlignY {
private static Container makeIt(String title, float alignment) {
String labels[] = {"-", "-", "-"};
JPanel container = new JPanel();
container.setBorder(BorderFactory.createTitledBorder(title));
BoxLayout layout = new BoxLayout(container, BoxLayout.X_AXIS);
container.setLayout(layout);
for(int i=0, n=labels.length; i<n; i++) {
JButton button = new JButton(labels[i]);
button.setAlignmentY(alignment);
container.add(button);
}
return container;
}
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Runnable runner = new Runnable() {
public void run() {
JFrame frame = new JFrame("Alignment Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container panel1 = makeIt("Top", Component.TOP_ALIGNMENT);
Container panel2 = makeIt("Center", Component.CENTER_ALIGNMENT);
Container panel3 = makeIt("Bottom", Component.BOTTOM_ALIGNMENT);
frame.setLayout(new GridLayout(1,3));
frame.add(panel1);
frame.add(panel2);
frame.add(panel3);
frame.setSize(423, 171);
frame.setVisible(true);
}
};
EventQueue.invokeLater(runner);
}
}

使用不同的对齐布局组件

package swingstudy.ch10;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.LayoutManager;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.OverlayLayout;
public class OverlaySample {
public static final String SET_MINIMUM = "Minimum";
public static final String SET_MAXIMUM = "Maximum";
public static final String SET_CENTRAL = "Central";
public static final String SET_MIXED = "Mixed";
static JButton smallButton = new JButton();
static JButton mediumButton = new JButton();
static JButton largeButton = new JButton();
public static void setupButtons(String command) {
if (SET_MINIMUM.equals(command)) {
smallButton.setAlignmentX(0.0f);
smallButton.setAlignmentY(0.0f);
mediumButton.setAlignmentX(0.0f);
mediumButton.setAlignmentY(0.0f);
largeButton.setAlignmentX(0.0f);
largeButton.setAlignmentY(0.0f);
} else if (SET_MAXIMUM.equals(command)) {
smallButton.setAlignmentX(1.0f);
smallButton.setAlignmentY(1.0f);
mediumButton.setAlignmentX(1.0f);
mediumButton.setAlignmentY(1.0f);
largeButton.setAlignmentX(1.0f);
largeButton.setAlignmentY(1.0f);
} else if (SET_CENTRAL.equals(command)) {
smallButton.setAlignmentX(0.5f);
smallButton.setAlignmentY(0.5f);
mediumButton.setAlignmentX(0.5f);
mediumButton.setAlignmentY(0.5f);
largeButton.setAlignmentX(0.5f);
largeButton.setAlignmentY(0.5f);
} else if (SET_MIXED.equals(command)) {
smallButton.setAlignmentX(0.0f);
smallButton.setAlignmentY(0.0f);
mediumButton.setAlignmentX(0.5f);
mediumButton.setAlignmentY(0.5f);
largeButton.setAlignmentX(1.0f);
largeButton.setAlignmentY(1.0f);
} else {
throw new IllegalArgumentException("Illegal Command: " + command);
}
// redraw panel
((JPanel) largeButton.getParent()).revalidate();
}
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
final ActionListener generalActionListener = new ActionListener() {
public void actionPerformed(ActionEvent event) {
JComponent comp = (JComponent) event.getSource();
System.out.println(event.getActionCommand() + " : "
+ comp.getBounds());
}
};
final ActionListener sizingActionListener = new ActionListener() {
public void actionPerformed(ActionEvent event) {
setupButtons(event.getActionCommand());
}
};
Runnable runner = new Runnable() {
public void run() {
JFrame frame = new JFrame("Overlay Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel() {
public boolean isOptimizedDrawingEnabled() {
return false;
}
};
LayoutManager overlay = new OverlayLayout(panel);
panel.setLayout(overlay);
Object settings[][] = {
{"Small", new Dimension(25,25), Color.white},
{"Medium", new Dimension(50,50), Color.gray},
{"Large", new Dimension(100,100), Color.black}
};
JButton buttons[] = {smallButton, mediumButton, largeButton};
for(int i=0, n=settings.length; i<n; i++) {
JButton button = buttons[i];
button.addActionListener(generalActionListener);
button.setActionCommand((String)settings[i][0]);
button.setMaximumSize((Dimension)settings[i][1]);
button.setBackground((Color)settings[i][2]);
panel.add(button);
}
setupButtons(SET_CENTRAL);
JPanel actionPanel = new JPanel();
actionPanel.setBorder(BorderFactory.createTitledBorder("Change Alignment"));
String actionSettings[] = {SET_MINIMUM, SET_MAXIMUM, SET_CENTRAL, SET_MIXED};
for(int i=0, n=actionSettings.length; i<n; i++) {
JButton button = new JButton(actionSettings[i]);
button.addActionListener(sizingActionListener);
actionPanel.add(button);
}
frame.add(panel, BorderLayout.CENTER);
frame.add(actionPanel, BorderLayout.SOUTH);
frame.setSize(400, 300);
frame.setVisible(true);
}
};
EventQueue.invokeLater(runner);
}
}

Component left = ...;
SpringLayout layout = new SpringLayout();
JPanel panel = new JPanel(layout);
Spring xPad = Spring.constant(5);
Spring yPad = Spring.constant(25);
SpringLayout.Constraints constraint = new SpringLayout.Constraints();
constraint.setConstraint(SpringLayout.WEST, xPad);
constraint.setConstraint(SpringLayout.NORTH, yPad);
frame.add(left, constraint);
这看起来并不是太复杂，但是当我们需要添加下一个组件，前一个组件的右边或是下边时，事情就会变得更为困难。我们不能仅是将组件添加额外的n个像素。我们必须实际的向前一个组件的边添加填充。要确定前一个组件的边，我们可以使用getConstraint()查询布局管理器，并传递我们所希望的边与组件，例如在layout.getConstraint(SpringLayout.EAST, left)来获得前一个组件右边的位置。由这个位置起，我们可以添加必须的填充，并将其关联到其他组件的边，如下面的代码所示：

Component right = ...;
Spring rightSideOfLeft = layout.getConstraint(SpringLayout.EAST, left);
Spring pad = Spring.constant(20);
Spring leftEdgeOfRight = Spring.sum(rightSideOfLeft, pad);
constraint = new SpringLayout.Constraints();
constraint.setConstraint(SpringLayout.WEST, leftEdgeOfRight);
constraint.setConstraint(SpringLayout.NORTH, yPad);
frame.add(right, constraint);
上面的方法可以工作得很好，但是随着组件数的增加，上面的方法就会变得十分繁琐。要减少其中的步骤，我们可以添加没有约束的组件，然后单独添加，通过SpringLayout的putConstraint()方法连接组件。

public void putConstraint(String e1, Component c1, int pad, String e2,
Component c2)
public void putConstraint(String e1, Component c1, Spring s, String e2,
Component c2)
这样，我们不需要查询边并亲自添加填充，putConstraint()调用可以为我们组合这些任务。为了演示，下面的代码片段为右边的组件添加了相同的组件约束，但是所用的是putConstraint()方法而是直接使用SpringLayout.Constraints：

Component left = ...;
Component right = ...;
SpringLayout layout = new SpringLayout();
JPanel panel = new JPanel(layout);
panel.add(left);
panel.add(right);
layout.putConstraint(SpringLayout.WEST, left, 5, SpringLayout.WEST, panel);
layout.putConstraint(SpringLayout.NORTH, left, 25, SpringLayout.NORTH, panal);
layout.putConstraint(SpringLayout.NORTH, right, 25, SpringLayout.NORTH, panel);
layout.putConstraint(SpringLayout.WEST, right, 20, SpringLayout.EAST, left);
为了有助于我们理解SpringLayout的使用，Sun有一个名为The Bean Builder的工作，https://bean-builder.dev.java.nt/。这个工具最初是要用于使用JavaBean组件的工作，但是也可以用于SpringLayout。图10-20显示了通过JavaWebStart启动时的样子。

10.14 小结