java - 需要有关 JComboBox 上的 itemStateChanged 的​​帮助

Question

我有三个 JComboBox，一个用于大陆，一个用于国家，另一个用于城市。所有数据均从数据库加载。

第一个 JComboBox 包含所有大陆。当我选择其中之一时，第二个 JComboBox 会加载相应的国家/地区。到目前为止都有效，因为我添加了“itemStateChanged”。

但是，当我选择一个国家/地区时，会再次调用事件“itemStateChanged”。是什么使我的第二个组合框与选定的第一个项目保持一致，或者(如果我执行“RemoveAllItems”)重复其内容？

有没有办法为每个 JComboBox 创建一个“itemStateChanged”？在 .NET 中，可以为每个组合框创建一个“SelectedIndexChanged”？

我的代码的某些部分:

public class MainFrame extends JFrame implements ItemListener 
{
…
private String iddistrito="VAZIO!!!";
private String idmunicipio="VAZIO!!!"; 
private boolean limpa=false;
private boolean populardistritos=false;
private boolean popularmunicipios=false;
private JComboBox cbFreguesiacliente = new JComboBox();
private JComboBox cbmunicipiocliente = new JComboBox();
private JComboBox cbdistritocliente = new JComboBox();
…
private void jbInit() throws Exception {
…
cbmunicipiocliente.addItemListener(this);
cbdistritocliente.addItemListener(this);     
…
}

这部分代码是我单击按钮时的内容，以启用我的组件:

private void btnNovocliente_actionPerformed(ActionEvent e) {
    populardistritos = true;
    cbdistritocliente.removeAllItems();
    preenchecbdistritos();
    populardistritos = false;
}

这段代码填充了第一个JComboBox的内容:

private void preenchecbdistritos(){
        query = "select Distrito from distritos;";
        try{
            Class.forName(JDBC_DRIVER);
            connection = DriverManager.getConnection(DATABASE_URL);
            statement = connection.createStatement();
            ResultSet resultset = statement.executeQuery(query);
            StringBuffer results = new StringBuffer();
            ResultSetMetaData metaData = resultset.getMetaData();
            int numberOfColumns = metaData.getColumnCount();
            cbdistritocliente.addItem("");
            while (resultset.next()) {
                for (int i =1; i<= numberOfColumns; i++) {
                    if (metaData.getColumnName(i).equals("Distrito")) {
                        cbdistritocliente.addItem(resultset.getObject(i).toString());
                    }
                }
            }
        } catch (ClassNotFoundException e) {
            JOptionPane.showMessageDialog(this,"rebentou no 1º catch " + e.toString(),"Inane error", JOptionPane.ERROR_MESSAGE);
        } catch (SQLException e) {
            JOptionPane.showMessageDialog(this,"rebentou no 2º catch " + e.toString(),"Inane error", JOptionPane.ERROR_MESSAGE);
        }
}

这是著名的事件，希望为每个 JComboBox 单独获取:

public void itemStateChanged(ItemEvent e) {
    if (populardistritos == false) {
        if (limpa == false) {
            if ((!cbdistritocliente.getSelectedItem().toString().equals("")) && (idmunicipio.equals("VAZIO!!!")))
            {
                query = "select id_distrito from distritos where distrito = '" + cbdistritocliente.getSelectedItem().toString() + "';";
                try{
                    Class.forName(JDBC_DRIVER);
                    connection = DriverManager.getConnection(DATABASE_URL);
                    statement = connection.createStatement();
                    ResultSet resultset = statement.executeQuery(query);
                    StringBuffer results = new StringBuffer();
                    ResultSetMetaData metaData = resultset.getMetaData();
                    int numberOfColumns = metaData.getColumnCount();
                    while (resultset.next()) {
                        for (int i =1; i<= numberOfColumns; i++) {
                            if (metaData.getColumnName(i).equals("id_distrito")) {
                                iddistrito = resultset.getObject(i).toString();
                            }
                        }
                    }
                        preenchecbmunicipios();    
                } catch (ClassNotFoundException e2) {
                } catch (SQLException e2) {
                }
            }
        }


        if (!cbmunicipiocliente.getSelectedItem().toString().equals(""))
        {
            query = "select id_municipio from municipios where municipio = '" + cbmunicipiocliente.getSelectedItem().toString() + "';";
            try{
                Class.forName(JDBC_DRIVER);
                connection = DriverManager.getConnection(DATABASE_URL);
                statement = connection.createStatement();
                ResultSet resultset = statement.executeQuery(query);
                StringBuffer results = new StringBuffer();
                ResultSetMetaData metaData = resultset.getMetaData();
                int numberOfColumns = metaData.getColumnCount();
                while (resultset.next()) {
                    for (int i =1; i<= numberOfColumns; i++) {
                        if (metaData.getColumnName(i).equals("id_municipio")) {
                            idmunicipio = resultset.getObject(i).toString();
                        }
                    }
                }
            } catch (ClassNotFoundException e2) {
            } catch (SQLException e2) {
            }
        }            
    }
}

这段代码填充了第二个JComboBox的内容:

private void preenchecbmunicipios(){
    if (!iddistrito.equals("VAZIO!!!")) {
        query = "select municipio from municipios where municipios.id_distrito = " + iddistrito + ";";
        populardistritos=true;
        //cbmunicipiocliente.removeAllItems();
        try{
            Class.forName(JDBC_DRIVER);
            connection = DriverManager.getConnection(DATABASE_URL);
            statement = connection.createStatement();
            ResultSet resultset = statement.executeQuery(query);
            StringBuffer results = new StringBuffer();
            ResultSetMetaData metaData = resultset.getMetaData();
            int numberOfColumns = metaData.getColumnCount();
            cbmunicipiocliente.addItem("");
            while (resultset.next()) {
                for (int i =1; i<= numberOfColumns; i++) {
                    if (metaData.getColumnName(i).equals("municipio")) {
                        cbmunicipiocliente.addItem(resultset.getObject(i).toString());
                    }
                }
            }
            populardistritos=false;
        } catch (ClassNotFoundException e) {
            JOptionPane.showMessageDialog(this,"rebentou no 1º catch do cbmunicipio com " + e.toString(),"Inane error", JOptionPane.ERROR_MESSAGE);
        } catch (SQLException e) {
            JOptionPane.showMessageDialog(this,"rebentou no 2º catch do cbmunicipio com " + e.toString(),"Inane error", JOptionPane.ERROR_MESSAGE);
        }            
    }
}

Answer 1

the docs告诉您该事件包含有关发起者的信息。因此只需检查 e.getItemSelectable().equals(firstSelectBox) 等即可。

希望有帮助。