Hi,

I need to implement this feature, I wonder if anyone could give me any pointers?  The requirement is to be able to drag a box (or group of boxes) onto another box, be able to provide a visual cue that the drop will have some effect, and then perform some action when the drop is complete.  The effect should be much the same as in windows explorer when you drag a file onto a folder to move it into that folder (i.e. the folder is highlighted when the item is dragged over it). 

At a first glance I can't see any events exposed by the flowchart to do this easily, I imagine I need to intercept and manipulate the box moving process somehow?  Any advice much appreciated, thanks

Jon

That indicates the box where the selection will be dropped by chaning the frame width. You might as well change something else, e.g. color ot pen style.

Stoyan

Actually, I just had a thought: I can handle the BoxModified and SelectionMoved events, if this occurs while the flowchart is in the 'dragged over' state then I know that the drop has occurred and I will have a reference to the box/selection which has been dropped, does that sound correct? 

Jon

The DragOver event is a WinForms drag+drop related event, which you would use if you wanted to drag items from other applications onto your flowchart and take action in response to that.

In Stoyo's example code, the line 'folderBox.PenWidth = 2' is the point at which 'folderBox' has something being dragged over it, and 'prevFolderBox.PenWidth = 0' occurs when that something is no longer positioned above folderBox.  You could insert your own code at these points to call your own methods to handle the dragging over.  You can then handle the MouseUp event, and if 'prevFolderBox' is not null, this would signal that the user has dropped the item. 

Hope that helps,
Jon

Ok we often get requests for handling 'drag over box/table' operations, I'll get a developer here implement some events for these in the next release of FlowChart.NET.

Hi Pascal,

We released version 3.2.3 on Monday, so the next release will be in mid-November. The events might be implemented much earlier though; leave a message at our support email address and we'll send you the daily build of the control when the events are available.

Stoyan

Jon,

That seems to happen because of an optimization used in FlowChart.NET to redraw the view quickly while dragging items or drawing new items. When the mouse button is pressed, all items that won't be moved or resized are painted in an offscreen bitmap, which is later blitted to the screen and only the dragged items are redrawn.

So even if you change the folder box pen width or color, the cache bitmap contains its old appearance and the odd effect occurs. I guess we can add a method to recreate that cache bitmap, which you could call after changing the folder box properties.

Stoyan

I looked through the mouse move code, and indeed the cache is recreated if an arrow is moved and arrow crossing shapes are enabled (e.g. drawing arcs at arrow crossing points). I guess that's done because these arcs might have to be redrawn even for arrows that are not moved, when some other arrows that are being modified cause the crossing point locations to change.

So if you create an invisible arrow attached to the dragged box, that could force the redraw. However it isn't a problem for us to make the now internal method that recreates the cache public, it's a single line of code. A developer can do this on Monday and we'll send you the daily build of the dll then; I believe we have your email address in our registration database.

Stoyan