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C# Discussion Thread
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Nov 7th, 2009

Problem with ComboBox display

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Hi all,
For a combobox I was trying to imitate the behaviour of this code example:http://msdn.microsoft.com/en-us/libr...luemember.aspx
So I have this class:

c# Syntax (Toggle Plain Text)
class Planet
    {
        private string myName;
        private double myGravitationalAcceleration;
 
        public Planet(string strName, double Acceleration)
        {
            this.myName = strName;
            this.myGravitationalAcceleration = Acceleration;
        }
 
        public string Name
        {
            get
            {
                return myName;
            }
        }
 
        public double GravitationalAcceleration
        {
            get
            {
                return myGravitationalAcceleration;
            }
        }
    }
class Planet
    {
        private string myName;
        private double myGravitationalAcceleration;

        public Planet(string strName, double Acceleration)
        {
            this.myName = strName;
            this.myGravitationalAcceleration = Acceleration;
        }

        public string Name
        {
            get
            {
                return myName;
            }
        }

        public double GravitationalAcceleration
        {
            get
            {
                return myGravitationalAcceleration;
            }
        }
    }

And a form with a combobox on it and this code:

c# Syntax (Toggle Plain Text)
public partial class InputData : Form
    {
        public InputData()
        {
            InitializeComponent();
            List<Planet> Planets = new List<Planet>();
            Planets.Add(new Planet("Earth at equator 0°", 9.78));           
            Planets.Add(new Planet("Earth at equinox 23.5°", 9.788));
            Planets.Add(new Planet("Earth at lattitude 50°", 9.81));
            Planets.Add(new Planet("Earth at pole 90°", 9.83));
            Planets.Add(new Planet("Moon", 1.63));
            Planets.Add(new Planet("Mars", 3.69));
            Planets.Add(new Planet("Venus", 8.87));
            Planets.Add(new Planet("Titan", 1.352));
            GraviAccelCombo.DataSource = Planets;
            //add names of properties here, seems cool!
            GraviAccelCombo.DisplayMember = "Name";
            GraviAccelCombo.ValueMember = "GravitationalAcceleration";
 
        }
 
        //private void GraviAccelCombo_SelectedIndexChanged(object sender, EventArgs e)
        //{
        //    GraviAccelCombo.Text = GraviAccelCombo.SelectedValue.ToString();
        //}
 
        private void GraviAccelCombo_SelectedValueChanged(object sender, EventArgs e)
        {
            if (GraviAccelCombo.SelectedIndex != -1)
            {
                GraviAccelCombo.Text = GraviAccelCombo.SelectedValue.ToString();
            }
        }
    }
public partial class InputData : Form
    {
        public InputData()
        {
            InitializeComponent();
            List<Planet> Planets = new List<Planet>();
            Planets.Add(new Planet("Earth at equator 0°", 9.78));           
            Planets.Add(new Planet("Earth at equinox 23.5°", 9.788));
            Planets.Add(new Planet("Earth at lattitude 50°", 9.81));
            Planets.Add(new Planet("Earth at pole 90°", 9.83));
            Planets.Add(new Planet("Moon", 1.63));
            Planets.Add(new Planet("Mars", 3.69));
            Planets.Add(new Planet("Venus", 8.87));
            Planets.Add(new Planet("Titan", 1.352));
            GraviAccelCombo.DataSource = Planets;
            //add names of properties here, seems cool!
            GraviAccelCombo.DisplayMember = "Name";
            GraviAccelCombo.ValueMember = "GravitationalAcceleration";

        }

        //private void GraviAccelCombo_SelectedIndexChanged(object sender, EventArgs e)
        //{
        //    GraviAccelCombo.Text = GraviAccelCombo.SelectedValue.ToString();
        //}

        private void GraviAccelCombo_SelectedValueChanged(object sender, EventArgs e)
        {
            if (GraviAccelCombo.SelectedIndex != -1)
            {
                GraviAccelCombo.Text = GraviAccelCombo.SelectedValue.ToString();
            }
        }
    }

What I want is: the user selects a planet(yeah there are moons too) name and in the display area of the combo I like to display the gravitational acceleration value. So if I select "Venus" from the dropdownlist, GraviAccelCombo.Text is equal to 8.87, but the word "Venus" gets still displayed instead of "8.87". Have a feeling it must be something very obvious, but I have no clue what so ever.
Any help is again greatly appreciated.

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ddanbe

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Nov 7th, 2009

Re: Problem with ComboBox display

I don't think it allows you to override the selection like that when it is databound. You could flip/flop the display member though:

C# Syntax (Toggle Plain Text)
    private void comboBox1_DropDown(object sender, EventArgs e)
    {
      comboBox1.DisplayMember = "Name";
    }
 
    private void comboBox1_DropDownClosed(object sender, EventArgs e)
    {
      comboBox1.DisplayMember = "GravitationalAcceleration";
    }
    private void comboBox1_DropDown(object sender, EventArgs e)
    {
      comboBox1.DisplayMember = "Name";
    }

    private void comboBox1_DropDownClosed(object sender, EventArgs e)
    {
      comboBox1.DisplayMember = "GravitationalAcceleration";
    }

sknake

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Nov 7th, 2009

Re: Problem with ComboBox display

Did not really solve my "problem" but you gave me hints to continue.
B.T.W. my design sucked

By introducing an extra textbox (as in the MSDN example btw) I got the best of both worlds: a name and a value. This makes it clearer for the user anyway.
Thanks for the effort.

Last edited by ddanbe; Nov 7th, 2009 at 3:20 pm.

ddanbe

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