TBMM/GCMM/CustomMessageBox.cs

using System.Windows.Forms;

namespace GCMM
{
    public partial class CustomMessageBox : Form
    {
        public bool ApplyToAll { get; private set; }
        public CustomMessageBox()
        {
            InitializeComponent();
            yesbtn.Click += (sender, e) =>
            {
                DialogResult = DialogResult.Yes;
                ApplyToAll = applyToAll.Checked;
                Close();
            };
            nobtn.Click += (sender, e) =>
            {
                DialogResult = DialogResult.No;
                ApplyToAll = applyToAll.Checked;
                Close();
            };
            /*cancelbtn.Click += (sender, e) =>
            {
                DialogResult = DialogResult.Cancel;
                Close();
            };*/
        }

        public CustomMessageBox(string message, string caption) : this()
        {
            content.Text = message;
            Text = caption;
        }
    }
}