FileDrop

Dragging and dropping files from the Windows Explorer on your .NET application form or on a control, can be implemented easy with the DragEnter and DragDrop events. You can check if the dropped items are files (DataFormats.FileDrop) and convert them to an array of strings.

C# example:

private void FormFileDropTester_DragEnter(object sender, DragEventArgs e)
{
  if (e.Data.GetDataPresent(DataFormats.FileDrop))
    e.Effect = DragDropEffects.Copy;
  else
    e.Effect = DragDropEffects.None;
}
    
private void FormFileDropTester_DragDrop(object sender, DragEventArgs e)
{
  string[] fileNames = (string[])e.Data.GetData(DataFormats.FileDrop);
  foreach (string fileName in fileNames)
  { 
    listBox1.Items.Add(fileName);
  }
}

It becomes more complicated if you want to reuse this source code in other forms or when you want to set restrictions on the file extensions. Therefore I have written a small FileDrop component (C#, .NET 2.0). It captures some Windows messages (WM_DROPFILES) and calls Win32 API functions like DragQueryFile and DragFinish.

You only have to add the FileDrop component to your form, link a control or a form (DropControl), set the list of allowed file extensions (AllowedFileExtensions) and implement the FilesDropped event. You can also create a derived component and add some extra logic in the CheckAcceptFile function.

Class diagram:

C# example:

private void FormFileDropTester_Load(object sender, EventArgs e)
{
  fileDrop1.AllowDrop = true;
  fileDrop1.DropControl = listBox1;
  fileDrop1.AllowedFileExtensions.Add("JPG");
  fileDrop1.AllowedFileExtensions.Add("BMP");
}

private void fileDrop1_FilesDropped(object source, SCIPbe.Controls.FilesDroppedEventArgs e)
{
  listBox1.Items.Clear();
  listBox1.Items.AddRange(e.FileNames.ToArray());
  listBox1.Items.Add("DropPoint.X = " +e.DropPoint.X.ToString());
  listBox1.Items.Add("DropPoint.Y = " + e.DropPoint.Y.ToString());
  listBox1.Items.Add("TotalFilesCount = " + e.TotalFilesCount.ToString());
  listBox1.Items.Add("AcceptedFilesCount = " + e.AcceptedFilesCount.ToString());
}

Copyrights and distribution

• The component is open source (Mozilla Public License 1.1) and may be freely distributed.
• The author doesn't give a warranty for error free running of this component and he doesn't give any support.
• See source code for history and more information about the classes, interfaces, properties, methods, events, ...

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FileDrop component

• Contents: FileDrop component and demo program with sources (C#, .NET 2.0, Visual Studio 2005)
• Version: 1.1 (2006-12-23)
• File size: 107.3 Kb
• Author: Stefan Cruysberghs

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