Drag and Drop not working in C# Winforms Application

13
votes

I am trying to create a windows form onto which I can drop a file/folder.

I have the following code in a WinForms app

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_DragEnter(object sender, DragEventArgs e)
    {
        Debug.Print("DragEnter");
    }

    private void Form1_DragDrop(object sender, DragEventArgs e)
    {
        MessageBox.Show("Dropped!");
    }
}

I have set the AllowDrop property to true. I've tried running the application in debug within Visual Studio. Based on answers to other similar questions, I've tried running the compiled exe as administrator. I've tried running the compiled exe not as administrator.

But whatever I do, I cannot get the DragDrop event to fire. The DragEnter event does fire, however. What am I missing?

8
c#winformsdrag-and-drop
Did you check if you accidentially lost the connection between DragDrop event and Form1_DragDrop handler? Sorry, if you did. - Fratyx
Is it a plain form, or have you added controls? If you drop onto a form's control, it will be that control that is responsible. - DonBoitnott
Drag and Drop will not work if you are running Visual Studio / your application as administrator and Windows Explorer is running under your normal account. - Archlight
@Archlight -- does anyone know why such ridiculousness exists? - rory.ap
Security. It used to be COM communication wrapped so it looked like Win32 api and it would be a BAD idea to allow one user running on the box to access another users memory.... How it is today, probably the same. - Archlight

8 Answers

30
votes

Is your DragDropEffect set appropriately? Try placing this in the DragEnter Event Handler Method:

    private void Form1_DragEnter(object sender, DragEventArgs e)
    {
        Console.WriteLine("DragEnter!");
        e.Effect = DragDropEffects.Copy;
    }

By default it was set to DragDropEffects.None so the Drop event wouldn't fire.

20
votes

For those who would read this because tips above do not work.

Notice that Drag&Drop won't work if you run Visual Studio or your app "As Administrator" as reported here: https://visualstudio.uservoice.com/forums/121579-visual-studio-ide/suggestions/2164233-fix-drag-and-drop-to-open-file-when-running-as-adm

6
votes

Don't forget in properties of the form to change AllowDrop to "True" Your code is probably fine but if this property is not enabled to true it won't work. It is set to false by default.

4
votes

try to use something like this in your Form1_DragEnter:

private void Form1_DragEnter(object sender, DragEventArgs e)
{
    if (e.Data.GetDataPresent(DataFormats.FileDrop))
        e.Effect = DragDropEffects.All;
    else
    {
        String[] strGetFormats = e.Data.GetFormats();
        e.Effect = DragDropEffects.None;
    }
}

this fires your Form1_DragDrop

0
votes

Have you written the MouseDown and MouseMove events of the object you are dragging from.

0
votes

Another very nasty and tricky problem can be that you have overriden OnHandleCreated, but forgot to call the base implementation. Then your application fails to set the required internal window settings to respect your AllowDrop property.

E.g., make sure to call base.OnHandleCreated(e) in your override, and you'll be fine.

0
votes

I also had this perplexing issue despite the form having AllowDrop set to true!

In my Windows Forms app (VS2017) I had to make sure I had set a valid Startup object: e.g myprojectname.Program and all was fine!

0
votes

I had a command line specified that was pointing to a file that no longer existed. Somehow that was preventing drag enter from firing. Once I removed it everything was fine again.