WinForms Drag & Drop (object not set to an instance)

Question

I have a Winforms app written in C#.

On my form I have two DataGridViews

I have set up a drag and drop operation between the two DataGridViews so that dragging from dataContact sends the int ID across to dataContactBusiness.

However on the Drop I get an error 'object not set to an instance'

When I step through my code I can see that DragEventArgs e contains the ID in its Data, so I fail to see why I am getting the error message.

My code is as follows -

private void dataContact_CellMouseDown(object sender, DataGridViewCellMouseEventArgs e)
{
    DataGridViewRow row = dataContact.Rows[e.RowIndex];
    int conID = (int)row.Cells["ID"].Value;
    dataContact.DoDragDrop(conID, DragDropEffects.All);
}

private void dataContactBusiness_DragEnter(object sender, DragEventArgs e)
{
   e.Effect = DragDropEffects.All;
}

private void dataContactBusiness_DragDrop(object sender, DragEventArgs e)
{
    string data = e.Data.GetData(DataFormats.Text).ToString();  //...error occurs here
}

Error Message

The data value of '5' is what I expected, so why the error?

o_weisman · Accepted Answer · 2013-10-22 12:35:29Z

3

I guess the format of the dragged data is not DataFormats.Text . You can put a breakpoint in the dataContactBusiness_DragDrop function and inspect the DragEventArgs to see what the format of the data is and change your parameter to GetData accordingly.

answered Oct 22, 2013 at 12:35

o_weisman

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1 Comment

PJW Over a year ago

Yes that's it - I was sending an int, but looking in e for text. Once I changed the DoDragDrop to 'dataContact.DoDragDrop(conID.ToString(), DragDropEffects.All);' the drop event picks up the value.

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