我正在尝试一点一点地学习Java，重新创建一个我用Python完成的应用程序——一个图书馆控制软件，非常基础。不过，我在事件处理方面遇到了问题，主要是因为(我认为)我在对 Swing 不太了解的情况下就全面了解了它，但边走边弄清楚了它。
到目前为止，这是我的代码:
public class SEHBV extends JFrame{
public SEHBV(){
super("SEHBV Biblio 2.0");
ImageIcon img = new ImageIcon("books.ico");
setIconImage(img.getImage());
JPanel p_ini, locar, devolver, buscar, administrar;
JLabel l_dia, l_mes, l_ano, loca_cs, loca_cl, loca_prazo, loca_cb, locado_state;
JTextField dia, mes, ano, loca_cs_tf, loca_cl_tf, loca_prazo_tf, loca_cb_tf, devolve_cod;
JTextArea loca_prazo_data, loca_oper_res, mostra_multa;
JButton data, loca_cb_bt, loca_commit, ver_multa;
JList<String> loca_s_res, loca_cb_res, atrasos, locados;
p_ini = new JPanel(new GridBagLayout());
GridBagConstraints i = new GridBagConstraints();
l_dia = new JLabel("Dia: ");
l_mes = new JLabel("Mês: ");
l_ano = new JLabel("Ano: ");
dia = new JTextField(6);
mes = new JTextField(6);
ano = new JTextField(6);
data = new JButton("Afirmar Data");
atrasos = new JList<String>();
atrasos.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
atrasos.setLayoutOrientation(JList.VERTICAL);
atrasos.setVisibleRowCount(10);
JScrollPane scroll_atrasos = new JScrollPane(atrasos);
atrasos.setBackground(Color.WHITE);
atrasos.setBorder(BorderFactory.createEtchedBorder(EtchedBorder.LOWERED));
i.fill = GridBagConstraints.HORIZONTAL;
i.gridx = 0;
i.gridy = 0;
p_ini.add(l_dia, i);
i.gridx = 1;
p_ini.add(dia, i);
i.gridx = 2;
p_ini.add(l_mes, i);
i.gridx = 3;
p_ini.add(mes, i);
i.gridx = 4;
p_ini.add(l_ano, i);
i.gridx = 5;
p_ini.add(ano, i);
i.gridx = 6;
p_ini.add(data, i);
i.gridy = 1;
i.gridx = 0;
i.gridwidth = 7;
p_ini.add(scroll_atrasos, i);
//GUI Locação
locar = new JPanel(new GridBagLayout());
GridBagConstraints l = new GridBagConstraints();
l.gridx = 0;
l.gridy = 0;
JPanel loca_socios = new JPanel(new FlowLayout());
JPanel loca_oper = new JPanel(new GridBagLayout());
GridBagConstraints o = new GridBagConstraints();
JPanel loca_busca = new JPanel(new GridBagLayout());
GridBagConstraints b = new GridBagConstraints();
locar.add(loca_socios, l); //Busca de Sócios na janela de Locação
loca_s_res = new JList<String>();
loca_s_res.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
loca_s_res.setLayoutOrientation(JList.VERTICAL);
loca_s_res.setModel(Runner.nome_socios);
loca_s_res.setVisibleRowCount(25);
JScrollPane scroll_loca_s = new JScrollPane(loca_s_res);
loca_s_res.setBorder(BorderFactory.createEtchedBorder(EtchedBorder.LOWERED));
loca_socios.add(scroll_loca_s);
l.gridx = 1;
locar.add(loca_oper, l); //Locação propriamente dita
o.weighty = 1;
o.weightx = 1;
o.anchor = GridBagConstraints.NORTHWEST;
o.insets = new Insets(1,1,1,1);
loca_cs = new JLabel("Código do Sócio: ");
o.fill = GridBagConstraints.HORIZONTAL;
o.gridx = 0;
o.gridy = 0;
loca_oper.add(loca_cs, o);
loca_cs_tf = new JTextField(5);
loca_cs_tf.setEditable(false);
loca_cs_tf.setBackground(Color.WHITE);
o.fill = GridBagConstraints.BOTH;
o.gridx = 1;
o.gridy = 0;
loca_oper.add(loca_cs_tf, o);
loca_cl = new JLabel("Código do Livro: ");
o.fill = GridBagConstraints.BOTH;
o.gridx = 0;
o.gridy = 1;
loca_oper.add(loca_cl, o);
loca_cl_tf = new JTextField(5);
o.fill = GridBagConstraints.BOTH;
o.gridx = 1;
o.gridy = 1;
loca_oper.add(loca_cl_tf, o);
loca_prazo = new JLabel("Prazo para devolução (em dias): ");
o.fill = GridBagConstraints.BOTH;
o.gridx = 0;
o.gridy = 2;
loca_oper.add(loca_prazo, o);
loca_prazo_tf = new JTextField(5);
o.fill = GridBagConstraints.BOTH;
o.gridx = 1;
o.gridy = 2;
loca_oper.add(loca_prazo_tf, o);
loca_prazo_data = new JTextArea();
loca_prazo_data.setBackground(getForeground());
o.gridx = 0;
o.gridy = 3;
o.gridwidth = 3;
loca_oper.add(loca_prazo_data, o);
loca_commit = new JButton("Realizar Locação");
o.fill = GridBagConstraints.BOTH;
o.gridx = 0;
o.gridy = 4;
o.gridwidth = 3;
loca_oper.add(loca_commit, o);
loca_oper_res = new JTextArea();
loca_oper_res.setBackground(getForeground());
o.gridy = 5;
loca_oper.add(loca_oper_res, o);
l.gridx = 2;
locar.add(loca_busca, l);
loca_cb = new JLabel("Chave de Busca: ");
b.fill = GridBagConstraints.HORIZONTAL;
b.gridx = 0;
b.gridy = 0;
loca_busca.add(loca_cb, b);
loca_cb_tf = new JTextField(20);
b.fill = GridBagConstraints.HORIZONTAL;
b.gridx = 1;
b.gridy = 0;
loca_busca.add(loca_cb_tf, b);
loca_cb_bt = new JButton("Busca Rápida");
b.fill = GridBagConstraints.HORIZONTAL;
b.gridx = 2;
b.gridy = 0;
loca_busca.add(loca_cb_bt, b);
loca_cb_res = new JList<String>();
loca_cb_res.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
loca_cb_res.setLayoutOrientation(JList.VERTICAL);
b.fill = GridBagConstraints.HORIZONTAL;
loca_cb_res.setBorder(BorderFactory.createEtchedBorder(EtchedBorder.LOWERED));
b.gridx = 0;
b.gridy = 1;
b.gridwidth = 3;
b.gridheight = 2;
loca_cb_res.setVisibleRowCount(25);
JScrollPane scroll_loca_cb = new JScrollPane(loca_cb_res);
loca_cb_res.setBorder(BorderFactory.createEtchedBorder(EtchedBorder.LOWERED));
loca_busca.add(scroll_loca_cb, b);
// Other Tabs of the GUI
//GUI Geral
JTabbedPane tp = new JTabbedPane();
tp.addTab("Página inicial (Alt+I)", null, p_ini, "pág. inicial");
tp.addTab("Locação (Alt+L)", locar);
tp.addTab("Devolução (Alt+D)", devolver);
tp.addTab("Busca Avançada (Alt+B)", buscar);
tp.addTab("Administração (Alt+A)", administrar);
tp.setMnemonicAt(0, KeyEvent.VK_I);
tp.setMnemonicAt(1, KeyEvent.VK_L);
tp.setMnemonicAt(2, KeyEvent.VK_D);
tp.setMnemonicAt(3, KeyEvent.VK_B);
tp.setMnemonicAt(4, KeyEvent.VK_A);
add(tp);
}
那么，假设我正在尝试处理 loca_commit JButton 的点击。我正在尝试根据 Java 教程和其他 StackOverflow 问题/答案创建一个事件处理程序 - 但该处理程序无法识别 loca_commit。现在我只是想让它工作，然后我将用它来调用一个方法，但如果我不能让它创建一个弹出窗口，那么，你明白我的意思了。
所以，到目前为止我的处理程序代码是这样的:
private class LocaHandler implements ActionListener{
public void actionPerformed(ActionEvent event){
String string = "";
if(event.getSource()==loca_commit)
string=String.format("Botão Apertado");
JOptionPane.showMessageDialog(null, string);
}
你们能在这里阐明一下吗？
最佳答案
核心问题可能是上下文之一，LocaHandler 可能没有任何 SEHBV 或 loca_commit 按钮的上下文，因此您无法引用它(它脱离了上下文)。
有几种方法可以解决这个问题...
你可以...
将 loca_commit 的引用传递给 LocaHandler 的实例，但除非您打算使用 LocaHandler 来处理多个操作，否则它确实没有意义，这意味着......
你可以...
让 LocaHandler 只负责做一件事，无论 loca_commit 需要它做什么。这将带您进入Actions API的领域。
怎么...
你可以...
利用 JButton 和 ActionEvent 的 actionCommand 属性支持
loca_commit = new JButton("Realizar Locação");
loca_commit.setActionCommand("locaCommit");
//...
private class LocaHandler implements ActionListener{
public void actionPerformed(ActionEvent event){
String string = "";
if("locaCommit".equals(event.getActionCommand()))
string=String.format("Botão Apertado");
JOptionPane.showMessageDialog(null, string);
}
这意味着您可以使用 LocaHandler 的同一实例来处理多个命令(通过扩展 if 语句)
我个人的偏好是使用 Actions API 或匿名类，专注于单一职责的处理程序，如果做得好，会增加类的可重用性
关于java - 事件处理 Swing 组件，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42825348/