Change DragVisual while Dragging

7 posts, 1 answers
  1. Thierry
    Thierry avatar
    22 posts
    Member since:
    Mar 2012

    Posted 23 Jul 2013 Link to this post

    Hi,

    I'm using the DragDropManager, and it works quite fine, but I cannot seem to figure out how to change a DragVisual while Dragging.

    the thing is, I have 2 different Dragging methods on an itemsControl : "internal" and "external".
    • For the "internal" one (i.e.: dragging one item around inside the itemsControl, like you do in your TileList), I'm setting the visual in the Draginitialize and it's fine.
    • but for the external one, I have a dragged object entering the itemsControl with its own dragVisual (and it should), then in the DragEnter handler, I do a few things (which work well) and I change the DragVisual, except... I cannot. I have not found a way to change the dragVisual in this handler.

    how should I do this, using the DragDropManager ? (I have also looked at the other handlers, but the only one I can find something about the visual is the DragInitialize handler, and it is not fired, since the dragged object does not come from inside the itemsControl)

    thanks

  2. Nick
    Admin
    Nick avatar
    593 posts

    Posted 24 Jul 2013 Link to this post

    Hello Thierry,

    The only way to modify the DragVisual is to save a reference to it in the DragInitialize event and use it later to modify it as you like. 

    Hope this helps! 

    Regards,
    Nik
    Telerik
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  4. Thierry
    Thierry avatar
    22 posts
    Member since:
    Mar 2012

    Posted 26 Jul 2013 Link to this post

    hi Nik,

    thank you for the answer. I tried what you suggested, but to no avail.
    I cannot seem to find a way to do this.
  5. Nick
    Admin
    Nick avatar
    593 posts

    Posted 31 Jul 2013 Link to this post

    Hello Thierry,

    What is the step you are not able to achieve? Can you share your efforts so far so I can be able to point you in the right direction?

    Thank you in advance! 

    Regards,
    Nik
    Telerik
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  6. Thierry
    Thierry avatar
    22 posts
    Member since:
    Mar 2012

    Posted 13 Aug 2013 Link to this post

    Hi nik.

    here is what I am trying to achieve :

    I have basically replicated your TileList control (which works perfectly fine), and am now trying to add a functionality to allow the user to add tiles to the tileList with a simple drag and drop.

    so  my screen is divided in 2 :
    1. TileList
    2. Tile pool : a simple list with "tiles" that I can drag to the tile list.

    My issue is : the "tiles" I drag from the tile pool are "default tiles" (no size, no background color, etc... just simple squares as layout)
    Now, when one of those tiles comes over the tileList, I would like the visual to switch to the exact visual the tile would have if I dropped it there.

    Is easy enough to get this visual, but I am at a lost on how to apply it as DragVisual.

    the ultimate goal here is to be able to drag almost anything from anywhere on to the tileList (this I already have done) with the visual being the right one when the dragged object is over the tileList (this is where I have trouble)

    i use telerik's DragDropManager to set up my drag & drop, but the DragVisual property is only available in the Draginitialize event, not the DragEnter or DragLeave, and I have found no way to set this DragVisual anywhere but in the Draginitialize


  7. Answer
    Yoan
    Admin
    Yoan avatar
    1070 posts

    Posted 16 Aug 2013 Link to this post

    Hi Thierry,

    Indeed, the idea is to cache the DragVisual in the DragInitialize event and update it in the DragOver/Enter/Leave events. 

    Let me try to explain further:

    Using our DragDropManager you can subscribe to the DragInitialize event. In its event handler you are allowed to set any UIElement or a DataTemplate (defined in your XAML) to the e.DragVisual property. When setting it you can save a reference to it like this:
    private var dragVisualLabel;
    private void OnDragInitialize(object sender, DragInitializeEventArgs args)
            {
                 
                this.dragVisualLabel = new Label() { Content = SomeContent, Background = new SolidColorBrush(Colors.Green) };
            args.DragVisual = this.dragVisualLabel;
            } 


    By doing so you will be able to modify your visual later:
    private void OnGiveFeedback(object sender, Telerik.Windows.DragDrop.GiveFeedbackEventArgs args)
            {            
                if (args.Effects == DragDropEffects.Move)
                {            
                    args.UseDefaultCursors = false;
                    args.SetCursor(Cursors.Hand);
                    this.dragVisualLabel.Background = new SolidColorBrush(Colors.Yellow);
                }
                else if (args.Effects == DragDropEffects.None)
                {             
                    args.UseDefaultCursors = false;
                    args.SetCursor(Cursors.None);
                    this.dragVisualLabel.Background = new SolidColorBrush (Colors.Red);
                }
                else
                {               
                    args.UseDefaultCursors = true;
                    this.dragVisualLabel.Background = new SolidColorBrush(Colors.Green);
                }
      
                args.Handled = true;
            }

    Please check this help article and this online demo for a reference. You can find the same example in you local copy of WPF demos.

    I hope this helps.

    Regards,
    Yoan
    Telerik
    TRY TELERIK'S NEWEST PRODUCT - EQATEC APPLICATION ANALYTICS for WPF.
    Learn what features your users use (or don't use) in your application. Know your audience. Target it better. Develop wisely.
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  8. Thierry
    Thierry avatar
    22 posts
    Member since:
    Mar 2012

    Posted 05 Sep 2013 Link to this post

    This helped ! :-)

    problem solved, thanks a lot

    (though I must add that this would not be possible, would I want to drag/drop between 2 different instances of the app. An easy access to the dragVisual in the other dragEvent functions would still be nice)
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