Add base tool to facilitate drag and drop support.

enable/tools/drop_tool.py

@@ -0,0 +1,50 @@
+#------------------------------------------------------------------------------
+# Copyright (c) 2014, Enthought, Inc.
+# All rights reserved.
+#
+# This software is provided without warranty under the terms of the BSD
+# license included in LICENSE.txt and may be redistributed only
+# under the conditions described in the aforementioned license.  The license
+# is also available online at http://www.enthought.com/licenses/BSD.txt
+# Thanks for using Enthought open source!
+#------------------------------------------------------------------------------
+""" Abstract base class for tools that handle drag and drop """
+
+from __future__ import absolute_import, print_function, division
+
+from enable.base_tool import BaseTool
+
+
+class BaseDropTool(BaseTool):
+    """ Abstract base class for tools that handle drag and drop """
+
+    def normal_drag_over(self, event):
+        """ Handle dragging over the component """
+        try:
+            result = self.accepts_drop(event.obj)
+            self.component.window.set_drag_result(result)
+        except Exception:
+            self.component.window.set_drag_result("error")
+            raise
+
+    def normal_dropped_on(self, event):
+        if self.accepts_drop(event.obj) != "none":
+            self.handle_drop(event.obj)
+
+    def accepts_drop(self, urls):
+        """ Whether or not to accept the drag, and the type of drag
+
+        The return value is either "none", if the drag is refused for the
+        dragged object types, or one of "copy", "move", or "link".
+
+        Subclasses should override this method.
+
+        """
+        raise NotImplementedError
+
+    def handle_drop(self, urls):
+        """ Handle objects being dropped on the component
+
+        Subclasses should override this method.
+        """
+        raise NotImplementedError