I was searching for possible solution for hours and could not find any. Hopefully someone can help me.
I managed to implement Multi Select WPF TreeView using the following answer: https://stackoverflow.com/a/6681993/1679059
It works nicely but I want to be able to drag selected items and drop them into the DataGrid.
In PreviewMouseMove
event handler previously selected items get deselected so I can't prevent that from happening.
I was trying to prevent deselecting items in PreviewMouseLeftButtonDown
event handler but at that point I cannot know if a user intends to select an item or drag selected items.
Can someone help me with that problem?