nana::dragdrop

The class dragdrop provides support of drag-and-drop operation. Unlike class simple_dragdrop, the dragdrop can transfer data between different processes.

The data to be transferred by the drag-and-drop operation is contained in a dragdrop::data object. The dragdrop::data object is created in a user-defined function in following way:

dragdrop dnd{fm};
dnd.prepare_data([]{
	dragdrop::data data;
	data.insert(std::filesystem::path{"/home/me/file.txt"}); //full path
	return data;
});

• constructors

  construct an instance

  dragdrop(window source);

  (0)

  dragdrop(const dragdrop&) = delete;

  (1)

  dragdrop& operator=(const dragdrop&) = delete;

  (2)

  dragdrop(dragdrop&&) = delete;

  (3)

  dragdrop& operator=(dragdrop&&) = delete;

  (4)

  Constructs an instance:
    0) Constructs an instance with a window. When the instance is instanced, the window immediately becomes dragdrop source window that user can drag the draggable content out of the window
    1,2,3,4) The copy and move constructors are deleted. The object of *dragdrop* is not copyable and movable.

  Exception

  std::invalid_argument
  throws if source is invalid.
  
  
• condition

  sets a condition checker

  void condition(std::function<bool()> predicate_fn);

  Sets a condition checker that determines whether the drag-and-drop operation can start. If a condition checker is not set, it always start drag-and-drop operation.

  Parameters

  predicate_fn
  Unary predicate which returns true for starting drag-and-drop operation.
  
  
• prepare_data

  transferred data

  void prepare_data(std::function<data()> generator);

  Sets a generator that makes the transferred data.

  Parameters

  generator
  Unary function which returns a dragdrop::data object that contains the transferred data.
  
  
• drop_finished

  drop handler

  void drop_finished(std::function<void(bool dropped, dnd_action executed_action, data& data_transferred)> finish_fn);

  The drop handler will be called when the drag-and-drop operation is finished.
  
  There are 3 parameters for the drop handler:
    0) dropped. Indicates whether the data is accepted by a target window.
    1) executed_action. Indicates the action returned by target window. Ignore if dropped is false.
    2) data_transferred The data object which is generated by the generator.

  Parameters

  finish_fn
  The drop handler function.