I've seen this done in Borland's Turbo C++ environment, but I'm not sure how to go about it for a C# application I'm working on. Are there best practices or gotchas to look out for?
9 Answers
Some sample code:
public partial class Form1 : Form {
public Form1() {
InitializeComponent();
this.AllowDrop = true;
this.DragEnter += new DragEventHandler(Form1_DragEnter);
this.DragDrop += new DragEventHandler(Form1_DragDrop);
}
void Form1_DragEnter(object sender, DragEventArgs e) {
if (e.Data.GetDataPresent(DataFormats.FileDrop)) e.Effect = DragDropEffects.Copy;
}
void Form1_DragDrop(object sender, DragEventArgs e) {
string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);
foreach (string file in files) Console.WriteLine(file);
}
}
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67
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4@Burnsys if you have the filepath from the drag operation, then you can read using
io.File
– SmithCommented May 24, 2013 at 23:51 -
Shouldn't the class be a sealed class to avoid making a virtual call on the
this.AllowDrop
? stackoverflow.com/questions/119506/…– CJBSCommented Feb 10, 2014 at 22:43 -
1Ugh, no. Set the AllowDrop property to True in the designer and reason it out from there. Commented Feb 10, 2014 at 23:02
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3
Be aware of windows vista/windows 7 security rights - if you are running Visual Studio as administrator, you will not be able to drag files from a non-administrator explorer window into your program when you run it from within visual studio. The drag related events will not even fire!
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7@Wayne Uroda: I thought my code wasn't working - heck it was giving me a big "No symbol" like this en.wikipedia.org/wiki/File:ProhibitionSign2.svg . Then I saw this answer and ran VS as a non-admin and presto it works! Thanks a million.– Derek WCommented Jun 3, 2013 at 18:09
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1Can't thank you enough for this, I would have given up unless I happened to find this post! It's as valid in Windows 10 in 2017 as it was when you wrote it.– CulmeCommented Jan 19, 2017 at 10:57
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Ok but what can we do? It is illogical? What if my program needs admin rights? Commented May 8, 2022 at 9:27
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@MericOzcan does this help stackoverflow.com/questions/2833709/… ? Commented May 9, 2022 at 14:53
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@WayneUroda I changed my program, now it selects files from path. Commented May 28, 2022 at 19:52
In Windows Forms, set the control's AllowDrop property, then listen for DragEnter event and DragDrop event.
When the DragEnter
event fires, set the argument's AllowedEffect
to something other than none (e.g. e.Effect = DragDropEffects.Move
).
When the DragDrop
event fires, you'll get a list of strings. Each string is the full path to the file being dropped.
You need to be aware of a gotcha. Any class that you pass around as the DataObject in the drag/drop operation has to be Serializable. So if you try and pass an object, and it is not working, ensure it can be serialized as that is almost certainly the problem. This has caught me out a couple of times!
Yet another gotcha:
The framework code that calls the Drag-events swallow all exceptions. You might think your event code is running smoothly, while it is gushing exceptions all over the place. You can't see them because the framework steals them.
That's why I always put a try/catch in these event handlers, just so I know if they throw any exceptions. I usually put a Debugger.Break(); in the catch part.
Before release, after testing, if everything seems to behave, I remove or replace these with real exception handling.
Here is something I used to drop files and/or folders full of files. In my case I was filtering for *.dwg
files only and chose to include all subfolders.
fileList
is an IEnumerable
or similar In my case was bound to a WPF control...
var fileList = (IList)FileList.ItemsSource;
See https://stackoverflow.com/a/19954958/492 for details of that trick.
The drop Handler ...
private void FileList_OnDrop(object sender, DragEventArgs e)
{
var dropped = ((string[])e.Data.GetData(DataFormats.FileDrop));
var files = dropped.ToList();
if (!files.Any())
return;
foreach (string drop in dropped)
if (Directory.Exists(drop))
files.AddRange(Directory.GetFiles(drop, "*.dwg", SearchOption.AllDirectories));
foreach (string file in files)
{
if (!fileList.Contains(file) && file.ToLower().EndsWith(".dwg"))
fileList.Add(file);
}
}
Another common gotcha is thinking you can ignore the Form DragOver (or DragEnter) events. I typically use the Form's DragOver event to set the AllowedEffect, and then a specific control's DragDrop event to handle the dropped data.
The solution of Judah Himango and Hans Passant is available in the Designer (I am currently using VS2015):
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1This wont work until you also use DragEnter and then set e.Effect = DragDropEfects.Move or something like that. thanks Commented Feb 27, 2022 at 9:53
Note that for this to work, you also need to set the dragDropEffect within _drawEnter...
private void Form1_DragEnter(object sender, DragEventArgs e)
{
Console.WriteLine("DragEnter!");
e.Effect = DragDropEffects.Copy;
}
Source: Drag and Drop not working in C# Winforms Application
ChangeWindowMessageFilter (0x0049, MSGFLT_ADD);
supposed to help in C#?