总结一下我在Java swing 编程实践中的一些经验以及要注意的问题
（1）如何在启动swing界面时指定组件（文本框）聚焦呢？
范例：
Java代码
- CreateMD5App frame = new CreateMD5App();
- frame.setVisible(true);
- frame.pathTF.requestFocus();
注意：requestFocus();必须放在this.setVisible(true);之后
（2）如何响应文本框的输入事件（有输入操作时触发的事件）
titleTF的类型是JTextArea
Java代码
- titleTF.getDocument().addDocumentListener(new DocumentListener() {
- @Override
- public void removeUpdate(DocumentEvent e) {
- // System.out.println("remove");
- try {
- checkTitle(titleTF);
- } catch (Exception e1) {
- e1.printStackTrace();
- }
- }
- @Override
- public void insertUpdate(DocumentEvent e) {
- // System.out.println("insert");
- try {
- checkTitle(titleTF);
- } catch (Exception e1) {
- e1.printStackTrace();
- }
- }
- @Override
- public void changedUpdate(DocumentEvent e) {
- // System.out.println("change");
- }
- });
（3）panel增加组件时，出现水平滚动条，而不是竖直滚动条。要求出现竖直滚动条，怎么办？
要求的效果：
实现方法：
Java代码
- otherRequestArgPane = new JPanel();// must be in front of
- // getAddNextButton() method
- otherRequestArgPane.setAutoscrolls(true);
- // 让panel 只显示竖直滚动条
- otherRequestArgPane.setLayout(new ModifiedFlowLayout());
- otherRequestArgJsPane = new JScrollPane(otherRequestArgPane);
- otherRequestArgJsPane.getHorizontalScrollBar().setAutoscrolls(false);
- otherRequestArgJsPane.getVerticalScrollBar().setAutoscrolls(true);
说明：把JPanel放在JScrollPane中。
ModifiedFlowLayout 是自定义的布局管理器，代码如下：
Java代码
- package com.swing.component;
- import java.awt.Component;
- import java.awt.Container;
- import java.awt.Dimension;
- import java.awt.FlowLayout;
- import java.awt.Insets;
- public class ModifiedFlowLayout extends FlowLayout {
- private static final long serialVersionUID = 5426056229476897767L;
- public ModifiedFlowLayout() {
- super();
- }
- public ModifiedFlowLayout(int align) {
- super(align);
- }
- public ModifiedFlowLayout(int align, int hgap, int vgap) {
- super(align, hgap, vgap);
- }
- public Dimension minimumLayoutSize(Container target) {
- // Size of largest component, so we can resize it in
- // either direction with something like a split-pane.
- return computeMinSize(target);
- }
- public Dimension preferredLayoutSize(Container target) {
- return computeSize(target);
- }
- private Dimension computeSize(Container target) {
- synchronized (target.getTreeLock()) {
- int hgap = getHgap();
- int vgap = getVgap();
- int w = target.getWidth();
- // Let this behave like a regular FlowLayout (single row)
- // if the container hasn't been assigned any size yet
- if (w == 0) {
- w = Integer.MAX_VALUE;
- }
- Insets insets = target.getInsets();
- if (insets == null) {
- insets = new Insets(0, 0, 0, 0);
- }
- int reqdWidth = 0;
- int maxwidth = w - (insets.left + insets.right + hgap * 2);
- int n = target.getComponentCount();
- int x = 0;
- int y = insets.top + vgap;// FlowLayout starts by adding vgap, so do
- // that here too.
- int rowHeight = 0;
- for (int i = 0; i < n; i++) {
- Component c = target.getComponent(i);
- if (c.isVisible()) {
- Dimension d = c.getPreferredSize();
- if ((x == 0) || ((x + d.width) <= maxwidth)) {
- // fits in current row.
- if (x > 0) {
- x += hgap;
- }
- x += d.width;
- rowHeight = Math.max(rowHeight, d.height);
- } else {
- // Start of new row
- x = d.width;
- y += vgap + rowHeight;
- rowHeight = d.height;
- }
- reqdWidth = Math.max(reqdWidth, x);
- }
- }
- y += rowHeight;
- y += insets.bottom;
- return new Dimension(reqdWidth + insets.left + insets.right, y);
- }
- }
- private Dimension computeMinSize(Container target) {
- synchronized (target.getTreeLock()) {
- int minx = Integer.MAX_VALUE;
- int miny = Integer.MIN_VALUE;
- boolean found_one = false;
- int n = target.getComponentCount();
- for (int i = 0; i < n; i++) {
- Component c = target.getComponent(i);
- if (c.isVisible()) {
- found_one = true;
- Dimension d = c.getPreferredSize();
- minx = Math.min(minx, d.width);
- miny = Math.min(miny, d.height);
- }
- }
- if (found_one) {
- return new Dimension(minx, miny);
- }
- return new Dimension(0, 0);
- }
- }
- }
（4）如何获取下拉框中选中的内容（不是index）
下拉框类型是JComboBox，初始化下拉框：
Java代码
- encodingComboBox = new JComboBox();
- // 设置下拉框中的选项
- for (int i = 0; i < SystemUtil.CHARSET_ARRAY.length; i++) {
- String charSet = SystemUtil.CHARSET_ARRAY[i];
- encodingComboBox.addItem(charSet);
- }
获取下拉框选中的内容：
Java代码
- String charset = (String) encodingComboBox.getSelectedItem();
界面如下：
