在 jComboBox 中显示数据

Question

我正在尝试将数据从另一个类中的数据库传递到 jcombobox 中的 JFrame，但只显示最后一行。下面是一个示例代码：

A级...

public String jcbNames() {
    try {
        con = connCC.getDBconnection();
        stm = con.createStatement();
        ResultSet rs = stm.executeQuery("Select customerName From appointment");

        while (rs.next()) {
            customer = (rs.getString(1));
        }
        con.close();

    } catch (SQLException ex) {
        ex.printStackTrace();
    } catch (ClassNotFoundException ex) {
        Logger.getLogger(Appointment.class.getName()).log(Level.SEVERE, null, ex);
    }
    return customer;
}

类 JFrame...

private void jCBCustomersActionPerformed(java.awt.event.ActionEvent evt) {                                             
    Appointment app = new Appointment();
    this.jCBCustomers.removeAllItems();
    this.jCBCustomers.addItem(app.jcbNames());
}

Answer 1

问题是您在 jcbNames 方法中只返回一个字符串，使用数组列表并将所有字符串添加到其中，然后将其作为数据库数据的集合返回。

所以改变你的方法或使用这个修改后的方法。

public ArrayList<String> jcbNames() {
    try {
        con = connCC.getDBconnection();
        stm = con.createStatement();
        ResultSet rs = stm.executeQuery("Select customerName From appointment");
        ArrayList<String> list = new ArrayList<>();
        while (rs.next()) {
            list.add(rs.getString(1));
        }
        con.close();

    } catch (SQLException ex) {
        ex.printStackTrace();
    } catch (ClassNotFoundException ex) {
        Logger.getLogger(Appointment.class.getName()).log(Level.SEVERE, null, ex);
    }
    return list;
}

和

private void jCBCustomersActionPerformed(java.awt.event.ActionEvent evt) {                                             
    Appointment app = new Appointment();
    this.jCBCustomers.removeAllItems();
    ArrayList<String> list =app.jcbNames();
    for (String str:list){
         this.jCBCustomers.addItem(str);
    }
}

如果您不想使用this.jCBCustomers.removeAllItems(); 来防止重复，请使用以下代码

private void jCBCustomersActionPerformed(java.awt.event.ActionEvent evt) {      
    Appointment app = new Appointment();

    // collect all of your current data in jcombobox
    ArrayList<String> current_list = new ArrayList<>();
    int count = this.jCBCustomers.getItemCount(); // get count of them
    for (int i = 0; i < count; i++) {
        current_list.add((String) this.jCBCustomers.getItemAt(i)); // add them to current list
    }

    // data that returned from database
    ArrayList<String> returned_from_db_list = jcbNames(); // calling jcbNames method

    /*
        for each string that has returned from database , 
        if it doesn't in the current_list 
        you can add it to jcombobox , so ...
    */ 
    for (String str : returned_from_db_list) {
        if ( !current_list.contains(str) ) { // check for existing in the current_list
            current_list.add(str); // adding fresh data to current_list!
            /*
                or you can add them directly to jcombobox and remove above statement.
                this.jCBCustomers.addItem(str); // add updated data to jcombobox
            */
        }
    }

    /* 
        if   ::: you use   current_list.add(str); in above for-each-loop ,
               now you must update jcombobox data !
        else ::: remove below loop.
    */
    for (String singleStr : current_list) {
        this.jCBCustomers.addItem(singleStr); // add updated data to jcombobox
    }
}