Question

I’m learning about accessor methods and enumeration. I wrote a public class ‘Car’ under the namespace ‘Vehicles’, and set private properties such as _manufacturer, _model, _year and _color. I’d like to write a single method to access properties and another to set/update them. This is my class:

using System;

namespace Vehicles
{
    public class Car
    {
        private string _manufacturer;
        private string _model;
        private string _year;
        private string _color;

        public void honkHorn()
        {
            // Add argument for a file name?
            // Code here to play a WAV file?
            MessageBox.Show("Honk!");
        }

        public string getCarInfo(string whichProperty)
        {
            switch (whichProperty)
            {
                case ("manufacturer"):
                   return _manufacturer;
                case ("model"):
                    return _model;
                case ("year"):
                    return _year;
                case ("color"):
                    return _color;
                default:
                    return null;
            }
        }

        public void setCarInfo(string whichProperty, string newValue)
        {
            switch (whichProperty)
            {
                case ("manufacturer"):
                    _manufacturer = newValue;
                    break;
                case ("model"):
                    _model = newValue;
                    break;
                case ("year"):
                    _year = newValue;
                    break;
                case ("color"):
                    _color = newValue;
                    break;
            }
        }
    }
}

And this is my form:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using Vehicles;

namespace CS_Enumeration
{
    public partial class Form1 : Form
    {
        public Car myCar = new Car();

        public Form1()
        {
            InitializeComponent();

            myCar.setCarInfo("manufacturer", "Ford");
            labelManfValue.Text = myCar.getCarInfo("manufacturer");

            myCar.setCarInfo("model", "Ranger");
            labelModelValue.Text = myCar.getCarInfo("model");

            myCar.setCarInfo("year", "2012");
            labelYearValue.Text = myCar.getCarInfo("year");

            myCar.setCarInfo("color", "Blue");
            labelColorValue.Text = myCar.getCarInfo("color");
        }

        private void button1_Click(object sender, EventArgs e)
        {
            myCar.honkHorn();
        }
    }
}

Is this really the best way to write a single method that can get/set? I first tried to cast a string value that matched the name of the object property and return the actual property, but that doesn’t work (unless someone knows how to cast a string to an object property?).

Thanks for the replies. This is all an exercise from a book I’m reading. It goes so far as to says that not everything should be public, but not everything should be private either. So how do I know when things should/should not be public/private? Sounds like the book is leading me in the wrong direction as to what’s good coding design. Anyone have any book suggestions for learning good coding design practices for Visual C#?

Answer 1

Don’t do this.

Use public properties instead and you gain type safety and a much more expressive usage of your class. In your current approach any typo in the property name string will cause a run-time exception instead of a compilation error.

Just use properties:

public class Car
{
   public string Manufacturer {get; set;}
   public string Model {get; set;}
   public string Year {get; set;}
   public string Color {get; set;}

  //..
}

Now you can just access the properties directly:

myCar.Manufacturer  = "Ford";
labelManfValue.Text = myCar.Manufacturer;

Also you should define a constructor that fully initializes a Car object, otherwise you might have some properties set, and others not.