事件處理Swing組件

Question

我試圖一點一點地學習Java，重新創建我用Python完成的應用程序-一個非常基本的庫控制軟件。 但是，我在使用事件處理時遇到了問題，主要是因為（我認為）我在不了解它的情況下就完全投入了Swing，但是在我進行時就弄清楚了。

到目前為止，這是我的代碼：

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);
}

因此，可以說我正在嘗試處理loca_commit JButton的單擊。 我正在嘗試根據Java教程和其他StackOverflow問題/答案創建事件處理程序，但是該處理程序無法識別loca_commit 。 現在，我只是想使其工作，然后將其用於調用方法，但是，如果無法使它創建彈出窗口，那您就明白了。

因此，到目前為止，我為處理程序編寫的代碼是：

    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);
        }

你們能在這里闡明一下嗎？

Answer 1

核心問題可能是上下文之一， LocaHandler可能沒有SEHBV或loca_commit按鈕的任何上下文，因此您不能引用它（它是上下文之外的）。

您可以通過幾種方法解決此問題...

你可以...

傳遞的參考loca_commit以實例LocaHandler ，但除非你打算利用LocaHandler處理多個動作，真的沒有任何意義，這意味着...

你可以...

使LocaHandler只負責一件事情，而loca_commit需要做的事情。 這將帶您進入Actions API領域

怎么...

你可以...

利用JButton和ActionEvent的actionCommand屬性支持

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);
}

這意味着您可以使用LocaHandler的同一實例來處理多個命令（通過擴展if語句）

我個人的喜好是使用Actions API或匿名類，將處理程序放在單個責任上，如果做得好，它將提高類的可重用性

Answer 2

一種使它起作用的方法是在初始化動作監聽器后將其附加到按鈕上。 對於您的情況，請嘗試以下操作：

loca_commit = new JButton("Realizar Locação");
//other code

loca_commit.addActionListener(new ActionListener() {

      @Override
      public void actionPerformed(ActionEvent e) {
             JOptionPane.showMessageDialog(null, "Hello");
      }
});
loca_oper.add(loca_commit, o);

請記住，這只是這樣做的一種方式。 有多種其他方法可以達到相同的結果。