java swing编程注意的一些问题
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2022-06-01 12:58:46
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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: