Library tutorials & articles
Drag and Drop in Windows Forms - A Primer
- Introduction
- Your First Drag and Drop
- The Listview Control
- The ListView ctnd.
- Dragging a Control around
- Control cntd. and Conclusion
Control cntd. and Conclusion
So not big bad evil code really but worth explaining. For the mousedown event we set our form level boolean, Dragging, to True. We record the mouse x and y position as the negative values of the mouseeventargs e.x and e.y respectively. This is because they will be used to Offset (subtract the current x and y by the original position when mousedown occurred) the mouseposition in the mousemove event. I then calculate the area which we will allow the button to move. This has to be the client left, right, top and bottom co-ordinates of the form.
For example the clipleft is the client x position of the mouse (distance of the mouse from the left of the screen) less the x position of the button on the form. This should give a current x value for the location of the form. I'm sure there is a better way of doing this because as you'll see if you try the example the four clip values I calculate are far from perfect and as ever I'm open to anyone giving me a better way of doing it. A job for another day perhaps. These values are then used to set the clip of the cursor (which limits mouse movement to the rectangle specified). The final line in that procedure is btnMove.Invalidate which causes it to be repainted on the form.
The mousemove event creates a point from the current mouse position, Me.PointToClient(MousePosition),
then Offsets by subtracting the x and y values we saved. They are subtracted
because they were set as negative values. The button's location is then changed
to this new point. Finally for the mouseup event the Dragging boolean is set
to false, the clip is set to nothing which releases the mouse again and the
button is invalidated for repainting. If you try this you'll se it works a treat
for the most part. I'm pretty sure you could improve upon this but as with so
many things in this article it's a start.
Conclusion
Drag and Drop is one of those cool things which is easier done than most think as you will have seen here. It's origins are based on improving the user experience and anything that makes our users happier is worth incorporating. I hope you can make some sense of this article and use it to make your users happier. Remember, though, to apply the Scotty rule by overestimating how difficult something is and how long it will take so that when they finally can drag and drop they'll think it's just as cool as you do and pay you more hopefully.
Microsoft Certified Applications Developer with 10 years experience developing web based applications using asp, asp.net for a Local Authority in Dublin. Clings to a firm belief that a web applicat...
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there is problem to select text (text-text example) after you dragged from source textbox it disallows to select some part
I wanted to write a simple form where the user could add a label to the form, rename it and move the label to where they needed it. Your code was right on the money and I can't thank you enough as it allowed to add a lot more functionality to the process that I never thought of before and it is working a treat.
If you find a control in VB that has a 'hwnd' property, you can drag it without too much hassle.
Add the following to the top of the form code:
Public Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Public Const HTCAPTION = 2
Public Const WM_NCLBUTTONDOWN = &HA1
You then, on the mousemove event, check to see if the mouse is pressed. If so, you call:
SendMessage( [the hwnd of the control], WM_NCLBUTTONDOWN, HTCAPTION, 0& )
The control should now be movable.
I am a self taught newbie (the worse sort) so please go gently.
My son has produce code to display and reorder jpeg thumbnails in a ListView and it works well, however, I would prefer Drop and Drag. I have sort of got it to work based on the example and a suggestion to remove 2 lines of code (see below) but it has 2 main problems. Note I am dragging within the same list (reordering) rather than dragging it somewhere else.
1/ Whenever I drop the thumbnail it always ends up at the bottom of the list.
2/ There is no indication where its about to be dropped.
Finally is there a way to display / bring into view an thumbnail image that has scrolled outside the window?
Private Sub ListViewDragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles ListView1.DragDrop, ListView1.DragDrop
Dim lvItem As ListViewItem
Dim destItem As ListViewItem
Dim destLv As ListView = CType(sender, ListView)
Dim clX As Integer = destLv.PointToClient(New Point(e.X, e.Y)).X
Dim clY As Integer = destLv.PointToClient(New Point(e.X, e.Y)).Y
If e.Data.GetDataPresent("System.Windows.Forms.ListViewItem", False) Then
'dragging a listview item
lvItem = CType(e.Data.GetData("System.Windows.Forms.ListViewItem"), ListViewItem)
'#' - destItem = CType(sender, ListView).GetItemAt(clX, clY)
'#' - destLv.Items.Insert(destItem.Index, lvItem.Clone)
lvItem.Remove()
destLv.Items.Add(lvItem)
End If
End Sub
Thanks in advance, Andrew
I've got 3 labels on a 143 by 126 picture box on a form. I need some code to stop the labels being dragged off of the picture box onto the rest of the form! At the minute, you can move the labels anywhere on the form and save the position. I only want to be able to move them in the picture box area.
Please help!
Thanks,
Jimbo.
Visual Basic 2005 Professional Edition:
I need to drag and drop an image from one PictureBox to another PictureBox where:
1) the image is visible while being dragged
2) the image can be dropped at any location within the target PictureBox
3) the image can be rotated within the target PictureBox
I wanted to be able to add the selected line to the end of the listview. As written I was not able to. I modified the initial load routine to add a blank line at the end of the list box, which allowed the addition before the blank line. Is there a better way to add to the end of a list view?
'Form level variables
Dim StartX, StartY As Integer
Dim Dragging As Boolean
Private Sub Label1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Label1.MouseDown
Dragging = True
StartX = e.X
StartY = e.Y
End Sub
Private Sub Label1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Label1.MouseMove
If Dragging = True Then
Label1.Left = (Label1.Left + e.X) - StartX
Label1.Top = (Label1.Top + e.Y) - StartY
'Could use a Point here as well if you wish
End If
End Sub
Private Sub Label1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Label1.MouseUp
Dragging = False
End Sub
I have problem when style of ListView1.View = View.LargeIcon
when I drag the icon between others, this icon put in the last position and not in the position where i put this
help me please, write me to a19992689@pucp.edu.pe
hello sir/mam
i m using vs.net 2003. i m developing a window application where i n i want to drag an image and drop to picturebox control .i m using following code but is not giving me the output.
please help me...
Private Sub Pic_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.PictureBox1.AllowDrop = True
End Sub
Private Sub PictureBox1_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles PictureBox1.DragEnter
If (e.Data.GetDataPresent(DataFormats.Bitmap)) Then
If (e.KeyState And ctrlMask) = ctrlMask Then
e.Effect = DragDropEffects.Copy
Else
e.Effect = DragDropEffects.Move
End If
Else
e.Effect = DragDropEffects.None
End If
End Sub
Private Sub PictureBox1_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles PictureBox1.DragDrop
PictureBox1.Image = e.Data.GetData(DataFormats.Bitmap)
End Sub
I had problems when i converted this code to C# resetting the clip rectangle in the MouseUp event handler i ended up doing it this way
Cursor.clip=Screen.Bounds(this);
This seemed to work but is not ideal anyone have any better suggestions ?
neil
Brian -- Thanks for you examples and thorough explanation. I'm new to .NET and found your article very useful just now. I tried your code, and you're right, the clipping was not quite perfect. I got a little better result after altering the calculations for clipwidth and clipheight.
Instead of
Dim clipwidth As Integer = Me.ClientSize.Width - (btnMove.Width - clipleft)
I tried
Dim clipwidth As Integer = Me.ClientSize.Width - btnMove.Width - 1
and then, more generally, in a ProcessMouseDownForAllControls Event
Dim clipwidth As Integer = Me.ClientSize.Width - CType(sender, Control).Size.Width - 1
The same change was done to the clipheight assignment.
Now to get it all to work with and on container controls ...
-- Steve
The sender in the drop subroutine is the text box that is being referenced.
This sure did save me a whole lot of wasted effort.
Thanks for the responses all the same!
Cheers
I did finally get the thing to work yesterday however but I ended up using other code. Now a new problem has risen where I have multiple textboxes that are to recieve the different information from the list view.
The issue is that I am having some trouble with knowing what the testbox name is in relation to the mouse over event. I think I have to compare the x and y of the mouse and the control but I'm not quite sure how this works.
Any suggestions?
If destItem Is Nothing Then
destLv.Items.Insert(destLv.Items.Count, lvItem.Clone)
Else
destLv.Items.Insert(destItem.Index, lvItem.Clone)
End If
Here we can check if we actually found an item in the second listview and if not put the item into the first available index.
If you are having problems getting at the item being dragged you may not be successfully putting it into the clipboard when dragging. Specifically this event's code:-
Private Sub ListViewItemDrag(ByVal sender As Object, ByVal e As System.Windows.Forms.ItemDragEventArgs) Handles ListView1.ItemDrag, ListView2.ItemDrag
DoDragDrop(e.Item, DragDropEffects.Move)
End Sub
Be sure to download the example project with the article that contains the complete code. And please folks. Any article is a starting point. To simply write it off as being of no help is a bit harsh.
Well I built the form as directed and even copied the code from the page.
The dragging from a listview to a listview does not work. So this item though interesting
is not useful at all.
I was having some trouble using this code to drag items from one listview to another myself.
The problem wasn't so much with dragging items from a listview, to a listview with items in it, provided I dropped the new item on one of the existing ones. However, if i just dropped it into an empty listview, or dropped it at some random point within the listview, the program would crash.
With a treeview, the exact point at which you are dropping the item is quite important, however, in a listview, we are often only moving items between listviews to populate the initially empty target.
In my case, I wanted to have a listview with a list of NFL Players, and a second, initially empty one, that I could drag and drop players into, as they were drafted in my fantasy league, leaving me a list of available players.
After spending some time on it, and taking a break (aka going to bed, then work) I took another look and the fix is rather obvious.
In Private Sub ListView DragDrop, I removed the following lines of code:
destItem = CType(sender, ListView).GetItemAt(clX, clY)
destLv.Items.Insert(destItem.Index, lvItem.Clone)
There are also now some variables that aren't needed and could be removed.
Then, after the line:
lvItem.Remove()
add a line:
destLv.Items.Add(lvItem)
This will drop the item from ListView1 into ListView2, add the bottom of the list (or vice versa)
Oddly enough, my first several attempt, were almost correct, I was just having a giant brain fart, and tried to add the item to the destination, before removing it from the originating ListView.
The dragging from a listview to a listview does not work. So this item though interesting
is not useful at all.
I am trying to take an item from a listview and put the text of that item into a textbox. The
article says how to do this by simply getting the listviewitem.text but this does not work either.
Perhaps i am missing a step somewhere.
Clearer info for tis newbie would be geatl appreciated
G
I found your article and source example fantastic - explained exactly what I needed to do, in the right tone too!
I have a question though. (Naturally)
I am designing a form that has a varying number of controls created at run time. Information about these controls will be stored in a database and the form will be generated around this information.
The question is "Is it possible to assign mouse events to controls created at runtime?"
For example, I create a label called "Label3" and position it where I want initially. The user then wants to move that label, which is one of say 500 on the form.
I have looked for a way to capture the name of the control using onclick and mouse down, and then assigning the name as a variable within the sub - failed on this, but not sure if its the right way.
Any pointers would be appreciated.
Regards,
Dave
This thread is for discussions of Drag and Drop in Windows Forms - A Primer.