单选按钮在组合框中显示值 [英] radio button show values in combo box

问题描述

我对这个if-else感到困惑，因为我是Java和Java的新手。 MySQL和我试图自己制作。

I confused with this if-else because I'm new in Java & MySQL and I tried to make it by myself.

public Menu() {
        initComponents();
        try {
            Class.forName("com.mysql.jdbc.Driver");
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/restaurant", "root", "");
            System.out.println("ODBC Connection Successful");

            showCategory();

        } catch (ClassNotFoundException | SQLException e) {
            System.out.println("ODBC Connection Failed" + e);

        }
    }

if - else

if - else

private void showCategory() {
        try {
            Statement stmt;
            stmt = con.createStatement();

            if (rbMFood.isSelected()) {
            ResultSet rs = stmt.executeQuery("SELECT * FROM menu_cat WHERE type_id = 'TY02'");
            while (rs.next()) {
                cmbMCat.addItem(rs.getString("menu_cat"));
            }

        } else {
            ResultSet rs = stmt.executeQuery("SELECT * FROM menu_cat WHERE type_id = 'TY01'");
            while (rs.next()) {
                cmbMCat.addItem(rs.getString("menu_cat"));
            }

            }
        } catch (Exception e) {

        }
    }

单选按钮

private void rbMFoodActionPerformed(java.awt.event.ActionEvent evt) {                                        
        // TODO add your handling code here:
        type = "Food";
    }                                       

    private void rbMDrinkActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        type = "Drink";
    }

我在程序的最后声明了这个函数

And I declare the function in the end of the program

private String type;

当我点击饮料/食物时，该类别仍属于饮品类别。

When I click drink / food, the category still drink's category.

数据库

非常感谢任何帮助！

推荐答案

您正在使用 rs.getString（menu_cat）但格式为 rs.getString（< Column Name>）但你是使用 rs.getString（< Table Name>）因为menu_cat是表的名称而不是列的名称。

You are using rs.getString("menu_cat") But the format is rs.getString(<Column Name>) But you are using rs.getString(<Table Name>) As "menu_cat" is name of the table and not the name of the column.

张贴构造函数

我从您发布的代码中看到的是，您已拨打构造函数中的showCategory（）。此方法负责填充 JComboBox cmbMCat 。现在，当您创建新的菜单时，正在填充 cmbMCat 。之后 cmbMCat 的项目列表不会改变。

What I see from the code you have posted, is that You have called showCategory() in the constructor. This method is responsible for populating the JComboBox cmbMCat. Now the cmbMCat is being populated when you are creating the new Menu. After that the items list of the cmbMCat does not change.

所以，我建议你打电话给来自 rbMFoodActionPerformed 和 rbMDrinkActionPerformed 方法的 showCategory（）。我希望这可以解决您的问题。

So, What I suggest is that you call the showCategory() from the rbMFoodActionPerformed and rbMDrinkActionPerformed methods. I hope this will solve your problem.

还要在之前添加 cmbMCat.removeAllItems（） Statement stmt; 删除 cmbMCat 中的所有项目，并使用新的项目列表重置它。

Also add cmbMCat.removeAllItems() before Statement stmt; to remove all the items that are there in the cmbMCat and reset it with a fresh list of items.

关于if-else的评论

更改 showCatagory（）如下所示：

private void showCategory() {
        cmbMCat.removeAllItems();
        try {
            PreparedStatement stmt; //Used Prepared statement
            String sql = "SELECT * FROM menu_cat WHERE type_id = ?";
            stmt = con.prepareStatement(sql);

            if (type.equals("Drink")) {
                stmt.setString("TY01");    
            } else {
                stmt.setString("TY02");
            }
                ResultSet rs = stmt.executeQuery();
                while (rs.next()) {
                    cmbMCat.addItem(rs.getString("menu_cat"));
                }

            }
        } catch (Exception e) {

        }
    }

另请注意， eventListener 代码应为：

private void rbMFoodActionPerformed(java.awt.event.ActionEvent evt){                                        
    type = "Food";
    showCategory();
}                                       

private void rbMDrinkActionPerformed(java.awt.event.ActionEvent evt){                                         
    type = "Drink";
    showCategory();
}

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