CODEWITHSUNDEEP
c#drag-and-dropflowlayoutpanel
leora
leora

Reputation: 196499

dragging user controls from one flowlayoutpanel to another

how can i add drag and drop capability of a custom usercontrol from 2 flowlayoutpanels?

Usercontrol keeps being null on the following line of code below

    private void flowLayoutPanel1_DragDrop(object sender, DragEventArgs e)
    {
        UserControl userControl = e.Data.GetData(typeof(UserControl)) as UserControl;

Upvotes: 3

Views: 2229

Answers (1)

Samuel
Samuel

Reputation: 38346

The problem with what you are doing is that to extract the data that is stored inside the drag, you have to specify the exact type.

control.DoDragDrop(new Label(), DragDropEffects.Move);

e.Data.GetDataPresent(typeof(Control)) // = false
e.Data.GetDataPresent(typeof(Label)) // = true

What you have to do is create a wrapper and use that for your drag-and-drop code.

class ControlWrapper
{
  public Control Control { get; private set; }
  public ControlWrapper(Control control) { Control = control; }
}

control.DoDragDrop(new ControlWrapper(new Label()), DragDropEffects.Move);

e.Data.GetDataPresent(typeof(ControlWrapper)) // = true

And your code now becomes

ControlWrapper controlWrapper = e.Data.GetData(typeof(ControlWrapper)) as ControlWrapper;
UserControl userControl = controlWrapper.Control as UserControl;

And trying not to sound too preachy, but you should check if the data exists in the form you want first. e.Data.GetDataPresent(typeof(ControlWrapper)) will tell you if it is that format.

Upvotes: 3

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