Question

Are there any controls that can dynamically create a group of radio buttons from a list of objects? Something similar to the CheckedBoxList control, but with mutually exclusive selection. This question points out this control doesn’t exist natively for WinForms but are there any third party controls that do this?

Answer 1

Control vendors can’t make any money with controls like that. Here’s some code to get your started:

using System;
using System.Drawing;
using System.Windows.Forms;

class RadioList : ListBox {
    public event EventHandler SelectedOptionChanged;

    public RadioList() {
        this.DrawMode = DrawMode.OwnerDrawFixed;
        this.ItemHeight += 2;
    }
    public int SelectedOption {
        // Current item with the selected radio button
        get { return mSelectedOption; }
        set { 
            if (value != mSelectedOption) {
                Invalidate(GetItemRectangle(mSelectedOption));
                mSelectedOption = value; 
                OnSelectedOptionChanged(EventArgs.Empty);
                Invalidate(GetItemRectangle(value));
            }
        }
    }
    protected virtual void OnSelectedOptionChanged(EventArgs e) {
        // Raise SelectOptionChanged event
        EventHandler handler = this.SelectedOptionChanged;
        if (handler != null) handler(this, e);
    }
    protected override void OnDrawItem(DrawItemEventArgs e) {
        // Draw item with radio button
        using (var br = new SolidBrush(this.BackColor))
            e.Graphics.FillRectangle(br, e.Bounds);
        if (e.Index < this.Items.Count) {
            Rectangle rc = new Rectangle(e.Bounds.Left, e.Bounds.Top, e.Bounds.Height, e.Bounds.Height);
            ControlPaint.DrawRadioButton(e.Graphics, rc,
                e.Index == SelectedOption ? ButtonState.Checked : ButtonState.Normal);
            rc = new Rectangle(rc.Right, e.Bounds.Top, e.Bounds.Width - rc.Right, e.Bounds.Height);
            TextRenderer.DrawText(e.Graphics, this.Items[e.Index].ToString(), this.Font, rc, this.ForeColor, TextFormatFlags.Left);
        }
        if ((e.State & DrawItemState.Focus) != DrawItemState.None) e.DrawFocusRectangle();
    }
    protected override void OnMouseUp(MouseEventArgs e) {
        // Detect clicks on the radio button
        int index = this.IndexFromPoint(e.Location);
        if (index >= 0 && e.X < this.ItemHeight) SelectedOption = index;
        base.OnMouseUp(e);
    }
    protected override void OnKeyDown(KeyEventArgs e) {
        // Turn on option with space bar
        if (e.KeyData == Keys.Space && this.SelectedIndex >= 0) SelectedOption = this.SelectedIndex;
        base.OnKeyDown(e);
    }
    private int mSelectedOption;
}