How to show open dialog box that can navigate to blender datablocks

Question

How to show open dialog box that can navigate to blender datablocks. I can show open dialog that can select .blend files, but how to select specific datablock just as 'File->Link' or 'File->Append' does?

Below is the code I am using ( copied from template ):

def read_some_data( context, filepath ):
  print("running read_some_data...")
  print( filepath )
  return {'FINISHED'}

class ImportSomeData( Operator, ImportHelper ):
    bl_idname = "import_test.some_data"
    bpy.ops.import_test.some_data is constructed
    bl_label = "Import Some Data"

    filename_ext = ".blend"

    filter_glob = StringProperty(
        default="*.blend",
        options={ 'HIDDEN' },
        )

def execute(self, context):
    return read_some_data(context, self.filepath)

Thanks!

Answer 1

You need to use bpy.data.libraries. The class has a function load which read the datablock of a blend file.

Here an example of how to draw such dialog box to append either a group or an object.

class open_blend_file(bpy.types.Operator, ImportHelper):
    """Import a .blend file to append model from"""
    bl_idname = "blend.open"
    bl_label = "Import"
    bl_options = {'UNDO'}
filter_glob: StringProperty(
    default="*.blend",
    options={'HIDDEN'},
)

group: BoolProperty()

def get_lib_groups(self,context):
    l = [];
    if os.path.exists(self.filepath) and self.filepath.endswith('.blend'):
        with bpy.data.libraries.load(self.filepath) as (data_from, data_to):
            groups = data_from.groups;
            # objects = data_from.objects;
            for g in groups:
                l.append((g,g,g));
    if len(l) == 0:
        l = [("None","None","None")];

    return l;

def get_lib_objects(self,context):
    l = [];
    if os.path.exists(self.filepath) and self.filepath.endswith('.blend'):
        with bpy.data.libraries.load(self.filepath) as (data_from, data_to):
            # groups = data_from.groups;
            objects = data_from.objects;
            for o in objects:
                l.append((o, o, o));
    if len(l) == 0:
        l = [("None","None","None")];

    return l;

lib_groups: EnumProperty(       
    name = "List of groups in the .blend file",
    description = "List of groups in the .blend file",
    items = get_lib_groups
);

lib_objects: EnumProperty(
    name = "List of objects in the .blend file",
    description = "List of objects in the .blend file",
    items = get_lib_objects
);


def draw(self, context):
    scene = bpy.context.scene;
    props = scene.property;
    layout = self.layout;

    row = layout.row();
    row.prop(props,'import_from', expand = True)     

    if props.import_from =='Groups':
        if len(self.lib_groups)>0:       
            row = layout.row();
            row.prop(self,'lib_groups', text = "Groups", icon = "GROUP")     
    else:
        if len(self.lib_objects)>0:       
            row = layout.row();
            row.prop(self,'lib_objects', text = "Objects", icon = "OBJECT_DATA")

def invoke(self, context, event):
    context.window_manager.fileselect_add(self)
    return {'RUNNING_MODAL'}

def execute(self, context):
    if self.group :
        name = self.lib_groups;
    else:
        name = self.lib_objects;

    if self.group:
        blend_file = self.filepath + "/Group/"
        bpy.ops.wm.append(directory=blend_file, link=False, filename=name, autoselect = True);

        group = bpy.data.groups.get(name); 
        if group is not None:
            bpy.ops.object.empty_add(type='PLAIN_AXES', location = (0,0,0));
            obj = get_active_object();
            obj.name = group.name;

            for o in group.objects:
                o.parent = obj;

            group.objects.link(obj);


    else:
        blend_file = self.filepath + "/Object/"
        bpy.ops.wm.append(directory=blend_file, link=False, filename=name, autoselect = True);

    return {'FINISHED'}

Answer 2

It seems there is now way to bring this dialog box that Append and Link are using. I've wrote some custom append operator by reworking the code from the previous answer, hope it will be useful.

import bpy
import os
bl_info = {
    "name": "Blender Custom Append",
    "author": "@Andrej730",
    "version": (1, 0),
    "blender": (2, 90, 0),
    "location": "",
    "description": "",
    "warning": "",
    "category": ""
}
def append_data_block(filepath, data_block_type, name, link=False, relative=False):
    with bpy.data.libraries.load(filepath, link=link, relative=relative) as (data_from, data_to):
        if name not in getattr(data_from, data_block_type):
            return {
                "data_block": None, 
                "msg": f"Data-block {data_block_type}/{name} not found in {filepath}"
            }
        getattr(data_to, data_block_type).append(name)
    return {
        "data_block": getattr(data_to, data_block_type)[0],
        "msg": ""
    }
class CustomBlendAppend(bpy.types.Operator):
    """Import a .blend file to append model from"""
    bl_idname = "blend.custom_append"
    bl_label = "Custom Blend Append"
    bl_options = {'UNDO'}
filepath: bpy.props.StringProperty(
    name="File Path", description="Filepath used to import from", 
    maxlen=1024, default="", subtype="FILE_PATH"
)

filter_glob: bpy.props.StringProperty(
    default="*.blend",
    options={'HIDDEN'},
)

def invoke(self, context, event):
    context.window_manager.fileselect_add(self)
    return {"RUNNING_MODAL"}

def get_lib_groups(self, context):
    l = [("0", "", "")]
    if os.path.exists(self.filepath) and self.filepath.endswith('.blend'):
        with bpy.data.libraries.load(self.filepath) as (data_from, data_to):
            for data_block_type in dir(data_from):
                data = getattr(data_from, data_block_type)
                if data:
                    item = (data_block_type,) * 3
                    l.append(item)
    return l

def get_lib_objects(self, context):
    l = [("", "", "")]
    if self.data_block_type != '0' and os.path.exists(self.filepath) and self.filepath.endswith('.blend'):
        with bpy.data.libraries.load(self.filepath) as (data_from, data_to):
            objects = getattr(data_from, self.data_block_type);
            for o in objects:
                l.append((o, o, o))
    return l

data_block_type: bpy.props.EnumProperty(       
    name = "Data Block Type",
    description = "List of data blocks in the .blend file",
    items=get_lib_groups,
)

data_block: bpy.props.EnumProperty(
    name = "List of objects in the .blend file",
    description = "List of objects in the .blend file",
    items=get_lib_objects,
)

def draw(self, context):
    layout = self.layout
    layout.label(text="Data Block Type")
    layout.prop(self, "data_block_type", text = "", icon = "GROUP")
    layout.label(text="Data Block")
    layout.prop(self,'data_block', text = "")     

def execute(self, context):
    if self.data_block_type == "0":
        self.report({"ERROR"}, "Select a data block type")
        return {"CANCELLED"}

    if self.data_block == "":
        self.report({"ERROR"}, "Select a data block")
        return {"CANCELLED"}

    if not os.path.exists(self.filepath):
        self.report({"ERROR"}, f"File not found:\n'{self.filepath}'")
        return {"CANCELLED"}

    db = append_data_block(self.filepath, self.data_block_type, self.data_block)
    if not db['data_block']:
        self.report({"ERROR"}, db["msg"])
        return {"CANCELLED"}

    props = context.scene.AppendedDatablockProps
    props.data_block_type = self.data_block_type
    props.data_block_name = db['data_block'].name
    props.blend_filepath = self.filepath
    print(db['data_block'], props.data_block_type, props.data_block_name, props.blend_filepath)

    return {"FINISHED"}



class AppendedDatablockProps(bpy.types.PropertyGroup):
    data_block_type: bpy.props.StringProperty(name="Data Block Type", default="")
    data_block_name: bpy.props.StringProperty(name="Data Block Name", default="")
    blend_filepath: bpy.props.StringProperty(name="Blend Filepth", default="")
def register():
    bpy.utils.register_class(CustomBlendAppend)
    bpy.utils.register_class(AppendedDatablockProps)
    bpy.types.Scene.AppendedDatablockProps = bpy.props.PointerProperty(type=AppendedDatablockProps)
def unregister():
    bpy.utils.unregister_class(CustomBlendAppend)
    bpy.utils.unregister_class(AppendedDatablockProps)
    del bpy.types.Scene.AppendedDatablockProps
if name == "main":
    register()
```