ImportHelper: Common methods for FileHandler drag and drop support

Provide common implementations for two operations that all Python
FileHandlers will typically use.

- `poll_file_object_drop` To be used inside the FileHandler `poll_drop`
   callback
- `invoke_popup` To be used inside the Operator `invoke` callback

The above code closely mirrors what is currently done inside the
existing Blender c++ FileHandlers.

Pull Request: https://projects.blender.org/blender/blender/pulls/119774

doc/python_api/examples/bpy.types.FileHandler.2.py

@@ -16,10 +16,11 @@ This ``directory`` and ``files`` properties now will be used by the
 """
 
 import bpy
+from bpy_extras.io_utils import ImportHelper
 from mathutils import Vector
 
 
-class ShaderScriptImport(bpy.types.Operator):
+class ShaderScriptImport(bpy.types.Operator, ImportHelper):
     """Test importer that creates scripts nodes from .txt files"""
     bl_idname = "shader.script_import"
     bl_label = "Import a text file as a script node"
@@ -28,8 +29,11 @@ class ShaderScriptImport(bpy.types.Operator):
     This Operator can import multiple .txt files, we need following directory and files
     properties that the file handler will use to set files path data
     """
-    directory: bpy.props.StringProperty(subtype='FILE_PATH', options={'SKIP_SAVE'})
-    files: bpy.props.CollectionProperty(type=bpy.types.OperatorFileListElement, options={'SKIP_SAVE'})
+    directory: bpy.props.StringProperty(subtype='FILE_PATH', options={'SKIP_SAVE', 'HIDDEN'})
+    files: bpy.props.CollectionProperty(type=bpy.types.OperatorFileListElement, options={'SKIP_SAVE', 'HIDDEN'})
+
+    """Allow the user to select if the node's label is set or not"""
+    set_label: bpy.props.BoolProperty(name="Set Label", default=False)
 
     @classmethod
     def poll(cls, context):
@@ -57,23 +61,25 @@ class ShaderScriptImport(bpy.types.Operator):
                 filepath = os.path.join(self.directory, file.name)
                 text_node.filepath = filepath
                 text_node.location = Vector((x, y))
+
+                # Set the node's title to the file name
+                if self.set_label:
+                    text_node.label = file.name
+
                 x += 20.0
                 y -= 20.0
         return {'FINISHED'}
 
     """
-    By default the file handler invokes the operator with the directory and files properties set.
-    In this example if this properties are set the operator is executed, if not the
-    file select window is invoked.
-    This depends on setting ``options={'SKIP_SAVE'}`` to the properties options to avoid
-    to reuse filepath data between operator calls.
-    """
+    Use ImportHelper's invoke_popup() to handle the invocation so that this operator's properties
+    are shown in a popup. This allows the user to configure additional settings on the operator like
+    the `set_label` property. Consider having a draw() method on the operator in order to layout the
+    properties in the UI appropriately.
 
+    If filepath information is not provided the file select window will be invoked instead.
+    """
     def invoke(self, context, event):
-        if self.directory:
-            return self.execute(context)
-        context.window_manager.fileselect_add(self)
-        return {'RUNNING_MODAL'}
+        return self.invoke_popup(context)
 
 
 class SHADER_FH_script_import(bpy.types.FileHandler):

scripts/modules/bpy_extras/io_utils.py

@@ -23,7 +23,10 @@ from bpy.props import (
     EnumProperty,
     StringProperty,
 )
-from bpy.app.translations import pgettext_data as data_
+from bpy.app.translations import (
+    pgettext_iface as iface_,
+    pgettext_data as data_,
+)
 
 
 def _check_axis_conversion(op):
@@ -96,12 +99,28 @@ class ImportHelper:
         description="Filepath used for importing the file",
         maxlen=1024,
         subtype='FILE_PATH',
+        options={'SKIP_PRESET', 'HIDDEN'}
     )
 
     def invoke(self, context, _event):
         context.window_manager.fileselect_add(self)
         return {'RUNNING_MODAL'}
 
+    def invoke_popup(self, context, confirm_text=""):
+        if self.properties.is_property_set("filepath"):
+            title = self.filepath
+            if len(self.files) > 1:
+                title = iface_("Import {} files").format(len(self.files))
+
+            if not confirm_text:
+                confirm_text = self.bl_label
+
+            confirm_text = iface_(confirm_text)
+            return context.window_manager.invoke_props_dialog(self, confirm_text=confirm_text, title=title, translate=False)
+
+        context.window_manager.fileselect_add(self)
+        return {'RUNNING_MODAL'}
+
     def check(self, _context):
         return _check_axis_conversion(self)
 
@@ -394,6 +413,19 @@ def unpack_face_list(list_of_tuples):
     return flat_ls
 
 
+def poll_file_object_drop(context):
+    """
+    A default implementation for FileHandler poll_drop methods. Allows for both the 3D Viewport and
+    the Outliner (in ViewLayer display mode) to be targets for file drag and drop.
+    """
+    area = context.area
+    if not area:
+        return False
+    is_v3d = area.type == 'VIEW_3D'
+    is_outliner_view_layer = area.type == 'OUTLINER' and area.spaces.active.display_mode == 'VIEW_LAYER'
+    return is_v3d or is_outliner_view_layer
+
+
 path_reference_mode = EnumProperty(
     name="Path Mode",
     description="Method used to reference paths",