How to clear a textbox if i drag the text out - vb.net

Question

I have code to drag files into a textbox, but I would also like to have code to drag the file out of the textbox, thus clearing it.
Anybody have any ideas?

Answer 1

You can use the DoDragDrop method to do a drag & drop operation. It returns a DragDropEffects value that specifies if the data actually has been dropped somewhere in which case you can clear the text box.
Since a drag & drop operation shouldn't start before the mouse has been moved a bit while pressing the mouse button you need to check for that in the MouseDown and MouseMove events. SystemInformation.DragSize tells you how far the mouse should be moved before a drag & drop operation starts.
In the MouseDown event check if you actually want to start a drag (i.e left button is pressed and text box actually contains text). Then create a rectangle using the mouse location and the size given by SystemInformation.DragSize. In the MouseMove event check if the mouse is dragged outside the rectangle and call DoDragDrop:
Private _dragStart As Boolean
Private _dragBox As Rectangle
Private Sub srcTextBox_MouseDown(sender As Object, e As MouseEventArgs) Handles srcTextBox.MouseDown
' a drag starts if the left mouse button is pressed and the text box actually contains any text
_dragStart = e.Button = MouseButtons.Left And Not String.IsNullOrEmpty(srcTextBox.Text)
If _dragStart Then
Dim dragSize As Size = SystemInformation.DragSize
_dragBox = New Rectangle(New Point(e.X - (dragSize.Width \ 2),
e.Y - (dragSize.Height \ 2)), dragSize)
End If
End Sub
Private Sub srcTextBox_MouseUp(sender As Object, e As MouseEventArgs) Handles srcTextBox.MouseUp
_dragStart = False
End Sub
Private Sub srcTextBox_MouseMove(sender As Object, e As MouseEventArgs) Handles srcTextBox.MouseMove
If Not _dragStart Or
(e.Button And MouseButtons.Left) <> MouseButtons.Left Or
_dragBox.Contains(e.X, e.Y) Then Return
Dim data As New DataObject()
data.SetData(srcTextBox.Text)
' you can optionally add more formats required by valid drag destinations:
' data.SetData(DataFormats.UnicodeText, Encoding.Unicode.GetBytes(srcTextBox.Text))
' data.SetData("UTF-8", Encoding.UTF8.GetBytes(srcTextBox.Text))
' data.SetData("UTF-32", Encoding.UTF32.GetBytes(srcTextBox.Text))
Dim dropEffect As DragDropEffects = srcTextBox.DoDragDrop(data, DragDropEffects.Move)
If (dropEffect = DragDropEffects.Move) Then
srcTextBox.Text = ""
End If
_dragStart = False
_dragBox = Rectangle.Empty
End Sub
Private Sub destTextBox_DragOver(ByVal sender As Object, ByVal e As DragEventArgs) Handles destTextBox.DragOver
If e.Data.GetDataPresent(GetType(String)) Then
e.Effect = e.AllowedEffect And DragDropEffects.Move
Else
e.Effect = DragDropEffects.None
End If
End Sub
Private Sub destTextBox_DragDrop(ByVal sender As Object, ByVal e As DragEventArgs) Handles destTextBox.DragDrop
If e.Data.GetDataPresent(GetType(String)) Then
destTextBox.Text = e.Data.GetData(GetType(String)).ToString()
End If
End Sub
Dragging the mouse in a TextBox usually starts text selection. The above code changes this behavior. Users can't use the mouse any more to select text. This is obviously not a good idea since users wouldn't expect that. To allow both text selection with the mouse and dragging you need to control the selection mechanism. This means you need to create your own text box class.
I would suggest a different approach: Use a label that shows the value as the dragging source and/or destination. To allow editing you can create a hidden text box. If the user double clicks on the label you hide the label and show the text box. After the user finishes editing (by hitting enter or cancel) or if the text box looses focus you hide the text box and show the label again.

Answer 2

Check out the DragLeave Event on the TextBox
Easiest way will probably be to store it as a variable or in clip board if leaving app.
Private Sub TheTextBox_DragLeave(sender As System.Object, e As System.EventArgs) Handles TheTextBox.DragLeave
Clipboard.SetText(TheTextBox.Text)
TheTextBox.Clear() 'Optional
End Sub
Then you'll need to code what happens when you mouse up of course, or drag into or whatever. You could clear the textbox in one of these steps. Depends on your implementation.