How to use the template_icon_view in 2.80

Question

Here I have a simple imaginary addon that is able to append 2 cubes from a blendfile. Instead of having buttons, I want to use a preview of the cubes. Such a preview you see in asset managers. (Tried to analyse their code, but got stuck). Here is the simple addon:

import bpy

# Here comes bl_info

# Add cube 1 to scene
class ADD_OT_cube1(bpy.types.Operator):
    bl_idname = 'add.cube1'
    bl_description = 'Adds a cube. Blue, small.'
    bl_category = 'SuperCube'
    bl_label = 'Add Blue Cube'

    def execute(self, context):
        path = os.path.dirname(__file__) + "/ojbects/cubes.blend\\Collection\\"
        object_name = "cube_01"
        bpy.ops.wm.append(filename=object_name, directory=path)
        return {"FINISHED"}

# Add cube 2 to scene
class ADD_OT_cube2(bpy.types.Operator):
    bl_idname = 'add.cube2'
    bl_description = 'Adds a cube. Red, Eating a banana.'
    bl_category = 'SuperCube'
    bl_label = 'Add Grazy Cube'

    def execute(self, context):
        path = os.path.dirname(__file__) + "/ojbects/cubes.blend\\Collection\\"
        object_name = "cube_02"
        bpy.ops.wm.append(filename=object_name, directory=path)
        return {"FINISHED"}


# The menu in the N-Panel 
class ADD_MT_menu(bpy.types.Menu):
    bl_label = "Add Cubes"
    bl_idname = "ADD_MT_menu"

    def draw(self, context):
        layout = self.layout
        layout.operator("add.cube1")
        layout.operator("add.cube2")



# Register Classes
classes = (
    ADD_OT_cube1,
    ADD_OT_cube2,
    ADD_MT_menu)

def register():
    from bpy.utils import register_class
    for cls in classes:
        register_class(cls)

def unregister():
    from bpy.utils import unregister_class
    for cls in classes:
        unregister_class(cls)

if __name__ == "__main__":
    register()

I suppose we can use the template_icon_view as documented on https://docs.blender.org/api/blender2.8/bpy.types.UILayout.html?highlight=template_icon_view#bpy.types.UILayout.template_icon_view but so far I didn’t get a clue.

Answer 1

There is an example burred in the blender source code repo

release/scripts/templates_py/ui_previews_dynamic_enum.py

tldr, its very similar to layout prop

class MyPanel(bpy.types.Panel):
    ...
def draw(self, context):
    layout = self.layout
    wm = context.window_manager

    row = self.layout.row()
    row.template_icon_view(wm, "my_previews", show_labels=True)

    row = self.layout.row()
    row.prop(wm, "my_previews")

that doesn't clarify much so some extra notes,

• the EnumProperty must be on the RNA of something built in . i tried it on PropertyGroup and that didn't seem to work, WindowManager is used in the example
• if the EnumProperty is defined as the result of a function, that function must be a top level function, methods are not allowed
• if the EnumProperty is defined as the result of a function, the 4th index into the enum (the last int) is the index of this enum's value inside the whole enum, populating this number with for index, myvar in enumerate(mylist): ... ret.append((myvar, myvar, '', 0, index)) is appropriate.
• if the EnumProperty is defined as the result of a function, the 3th index into the enum (the 2nd to last int) is the icon_id which can be a custom icon, be aware custom icons require care, if python's objects holding load custom icons get de-referenced that can cause icons to break.

the example linked above is quite a good example.

def get_my_enum(self, context) -> list[tuple[str, str, str, int int]]:
    if not context: return None
    return [
      ('foo', 'foo', '', 0, 0),
      ('bar' 'bar', '', 0, 1),
    ]
def register():
    bpy.types.WindowManager.my_enum = bpy.props.EnumProperty(items=get_my_enum)

I would love to find docs on what this magic tuple is, maybe its a standard enum property item but the docs don't clarify argument to attribute ordering there