using System;
using System.Windows.Forms;
using System.Diagnostics;
using System.IO;
 
namespace BryanWinForms1 {
    public partial class Form1 : Form {
 
        private delegate void DelegateOpenFile(String s); //define delegate type
        DelegateOpenFile _openFileDelegate; //declares a delegate instance
 
        public Form1() {
            InitializeComponent();
            this.AllowDrop = true; //must set this to true, for dragDrop to work
			//delegate needed so Form1_DragDrop() can asynchronously
			//invoke our program's OpenFile() method
            _openFileDelegate = new DelegateOpenFile(this.OpenFile); //instantiates delegate
        }
 
        private void openToolStripMenuItem_Click(object sender, EventArgs e) {
            OpenFileDialog openDlg = new OpenFileDialog();
            openDlg.Filter = "Any File (*.*)|*.*";
            openDlg.FileName = "";
            openDlg.CheckFileExists = true;
            openDlg.CheckPathExists = true;
 
            if (openDlg.ShowDialog() != DialogResult.OK)
                return;
 
            OpenFile(openDlg.FileName);
        }
 
        private void OpenFile(string sFile) {
            //insert appropriate file-opening code here...
            MessageBox.Show("\"" + sFile + "\" will be opened.");
        }
 
        private void Form1_DragEnter(object sender, DragEventArgs e) {
			//we're only interested if a FILE was dropped on the form
            if (e.Data.GetDataPresent(DataFormats.FileDrop))
                e.Effect = DragDropEffects.Copy;
            else
                e.Effect = DragDropEffects.None;
        }
 
        private void Form1_DragDrop(object sender, DragEventArgs e) {
			//good idea to use try-catch block, in case something goes wrong
			try {
                Array a = (Array)e.Data.GetData(DataFormats.FileDrop);
                if (a != null) {
                    // Extract string from first array element
                    // (ignore all files except first if number of files are dropped).
                    string s = a.GetValue(0).ToString();
                    // Call OpenFile asynchronously.
                    // Explorer instance from which file is dropped is not responding
                    // the entire time that the DragDrop handler is active, so we need to return
                    // immidiately (especially if OpenFile shows MessageBox).
                    this.BeginInvoke(_openFileDelegate, new Object[] { s });
                    this.Activate();        // in the case Explorer overlaps this form
                }
            }
            catch (Exception ex) {
                Trace.WriteLine("Error in DragDrop function: " + ex.Message);
                // don't show MessageBox here - Explorer is waiting !
            }
        }
 
		//next right-brace ends Form1 class
    }
	//next right-brace ends namespace
}