Question

Gretings

I need to have a custom control for my application. Basically its an expression editing GUI. You have, say, expression:

If variable_x is greater than variable_y

And you can click on “greater than” and change it to other comparator (like, equal to or less than).

The control thus must look like a label, but when you click it, it must show a dropdown (like combobox does) that has a listview inside (or maybe some other control) so that user can choose something. In a sense, i need a combobox without the box itself, replaced by something else (in this case, a label).

I know how to make custom controls, i understand i must somehow DropDown on mouse click or enter keypress, and hook events so that when whatever i dropped has closed, the choice is made, and also somehow track if user clicked elsewhere so i can close this dropdowned control. But i dont know if this is easy to do (some built-in method exists) or i have to do it all myself? Dont want to redevelop the wheel….

Please tell me if there are easy ways to do this.

Thanks!

Answer 1

You can extend the ComboBox control to update the DropDownStyle on Enter and LostFocus events.

public partial class MyComboBox : ComboBox
{
    public MyComboBox()
    {
        InitializeComponent();

        this.Dock = DockStyle.Fill;

        this.SelectionChangeCommitted += this.OnComboBoxSelectionChangeCommitted;
        this.Enter += this.OnControlEnter;
        this.LostFocus += this.OnComboBoxLostFocus;
    }

    private void OnControlEnter(object sender, EventArgs e)
    {
        this.DropDownStyle = ComboBoxStyle.DropDownList;
    }

    private void OnComboBoxLostFocus(object sender, EventArgs e)
    {
        this.DropDownStyle = ComboBoxStyle.Simple;
    }

    private void OnComboBoxSelectionChangeCommitted(object sender, EventArgs e)
    {
        // Notify to update other controls that depend on the combo box value
    }
}