java swing编程注意的一些问题

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：

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

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：

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：

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：

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：

String charset = (String) encodingComboBox.getSelectedItem();

 界面如下：