DropTarget hint and DropHighlightAdorner background brush

[mangoyoga80]

What changed?

• Added some null checking in DefaultDropHandler.
• Minor changes to base class DropTargetAdorner with null check and some base properties

Feature DropTargetHighlightBrush

• Added new feature for changing the brush of highlight adorner.
• Feature is enabled through attached property dd:DragDrop.DropTargetHighlightBrush.
• Updated TreeView\Bound sample
  

Feature DropHint

• Added new feature for drop hint adorners to illustrate to the user what drop targets are available for a given drag source.
• Added attached property dd:DragDrop.UseDropTargetHint to enable the feature
• Added attached property dd:DragDrop.DropHintDataTemplate to override datatemplate for displaying hint
• Made DragDrop.TryGetDropHandler and DragDrop.TryGetDropInfoBuilder internal
• New method IDropTarget.DropHint and new properties on IDropInfo which may be breaking change
• dd:DragDrop.UseDropTargetHint added in SettingsView to enable for all demos using these settings
• The gif demonstrates the functionality
  
• Updated sample Mixed\DragDropContext to use Hint and Error hints
  

Closed issues.
#487 Added drop target hints
#488 Added the ability to change the brush of hint adorner.

[bsundsbo]

@punker76 any chance you are able to take a look at this PR in the near future?

Happy Easter

[bsundsbo]

@punker76 any chance you are able to take a look at this PR in the near future?

Happy Easter

@punker76 Hi. I just wanted to follow up on this PR in case you have more time these days :)

[punker76]

@bsundsbo I will take a look in next days

[punker76]

Hi @mangoyoga80, I've finally had a look at your changes! I really like the feature. I only have one concern at the moment. Since an adorner is also used here for highlighting, the DropTargetAdorner is now always behind the HighlightAdorner. This cannot be prevented, as in WPF all adorners always get the same zIndex in the AdornerLayer.

But I already have an idea how we can get this under control. Perhaps I will first adopt your changes and then build my idea on them. But in any case, thanks for your contribution here!!!

/cc @bsundsbo

[mangoyoga80]

Hi @mangoyoga80, I've finally had a look at your changes! I really like the feature. I only have one concern at the moment. Since an adorner is also used here for highlighting, the DropTargetAdorner is now always behind the HighlightAdorner. This cannot be prevented, as in WPF all adorners always get the same zIndex in the AdornerLayer.

But I already have an idea how we can get this under control. Perhaps I will first adopt your changes and then build my idea on them. But in any case, thanks for your contribution here!!!

/cc @bsundsbo

I've not seen that issue as I've not used similar scenarios. Great you have some ideas how to fix.
Glad you like the feature