ComboBox - Set first display item in drop down list

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ian_jacobsen@hotmail.com - 11 Oct 2005 21:46 GMT

I have a ComboBox that contains values 0, 50, 100, 150, 200, 250, 300,
350, 400, 450, 500. Let's say the user types in a value of 425, and
then clicks the drop down list. When the list drops down, the first
item in the list is 0. How can I set the first item in the list to the
nearest value, say 400, while retaining the value 425 in the Text
property? I know that this is done in Outlook (on the Time fields when
adding a new appointment to the calendar), so one should be able to do
this with a standard ComboBox control.

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stephen.mcfall@gmail.com - 12 Oct 2005 02:11 GMT

You are looking for autocomplete functionality, you could inherit from
the ComboBox and write something like this ..

        public void MyComboBox_KeyPress(object sender,
System.Windows.Forms.KeyPressEventArgs e)
        {
            if(Char.IsControl(e.KeyChar))
            {
                return;
            }

            string toFind = this.Text.Substring(0, this.SelectionStart) +
e.KeyChar;
            int index = this.FindStringExact(toFind);

            if(index == -1)
            {
                index = this.FindString(toFind);
                LastSelectedIndex = index;
            }

            if (index == -1)
            {
                return;
            }

            this.SelectedIndex = index;
            this.SelectionStart = toFind.Length;
            this.SelectionLength = this.Text.Length - this.SelectionStart;
            e.Handled = true;
        }

Or you could use the excellent Genghis library at
http://www.sellsbrothers.com/tools/genghis/ built by Chris Sells and
his mates

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ian_jacobsen@hotmail.com - 12 Oct 2005 15:14 GMT

Unfortunately I'm not looking for autocomplete functionality. I have a
value in the ComboBox that does not appear in its drop down list. When
I drop down the list, I want the nearest match to be selected without
changing the current value.

So far I have a custom control that I inherited from
System.Windows.Forms.ComboBox, and I have the following code attempting
to do this.

protected override void OnDropDown(EventArgs e)
{
    string strValue = this.Text;
    int nValue = Convert.ToInt32(strValue);

    for (int i = 0; i < this.Items.Count; i++)
    {
        int nItem = Convert.ToInt32(this.Items[i].ToString());
        if (nValue >= nItem && nValue < nItem + 50)
        {
            this.SelectedIndex = i;
            break;
        }
    }

    base.OnDropDown(e);

    this.Text = strValue;
}

If I remove "this.Text = strValue;", the nearest value is selected
however the Text property will now contain this new selected value. I
want to select the nearest value when the list drops down (for display
purposes), but at the same time retain the value in the Text property.

--IAN

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ian_jacobsen@hotmail.com - 14 Oct 2005 21:45 GMT

Ok, I stumbled upon the solution myself. I'm using it as a time picker
control.

public class TimePicker : ComboBox
{
    bool m_fIsDropDown = false;
    string m_strTime = string.Empty;
    int m_nSelectedIndex = -1;

    public TimePicker() : base()
    {
    }

    private void LoadTimes()
    {
        if (this.Items.Count < 1)
        {
            DateTime t = new DateTime(2005, 10, 11, 0, 0, 0, 0);
            while (t < new DateTime(2005, 10, 12))
            {
                this.Items.Add(t.ToShortTimeString());
                t = t.AddMinutes(30);
            }
        }
    }

    protected override void OnCreateControl()
    {
        base.OnCreateControl();

        LoadTimes();
    }

    protected override void OnDropDown(EventArgs e)
    {
        base.OnDropDown(e);

        m_strTime = this.Text;
        DateTime dtmValue = DateTime.Now;
        try
        {
            dtmValue = Convert.ToDateTime(m_strTime);
        }
        catch
        {
            return;
        }

        for (int i = 0; i < this.Items.Count; i++)
        {
            DateTime dtmItem = Convert.ToDateTime(this.Items[i].ToString());
            if (dtmValue >= dtmItem && dtmValue < dtmItem.AddMinutes(30))
            {
                this.SelectedIndex = i;
                m_nSelectedIndex = i;
                break;
            }
        }

        m_fIsDropDown = true;
    }

    protected override void OnMouseDown(MouseEventArgs e)
    {
        if (m_fIsDropDown == true)
        {
            this.SelectedIndex = m_nSelectedIndex;
            this.Text = m_strTime;
        }
        else
        {
            base.OnMouseDown(e);
        }
    }

    protected override void OnMouseUp(MouseEventArgs e)
    {
        if (m_fIsDropDown == true)
        {
            this.SelectedIndex = m_nSelectedIndex;
            this.Text = m_strTime;
            m_fIsDropDown = false;
        }
        else
        {
            base.OnMouseUp(e);
        }
    }
}

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ComboBox - Set first display item in drop down list

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