example async drag-n-drop

examples/trello_cards/async-main.py

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+#!/usr/bin/env python3
+import asyncio
+from dataclasses import dataclass
+from functools import partial
+from typing import Optional, Tuple
+
+from nicegui import app, ui
+
+
+@dataclass
+class ToDo:
+    title: str
+
+
+@ui.page('/')
+def main():
+    def make_droppable_column(name: str) -> ui.column:
+        col = ui.column().classes('bg-blue-grey-2 w-60 p-4 rounded shadow-2')
+        with col:
+            ui.label(name).classes('text-bold ml-1')
+        col.on('dragover.prevent', partial(on_dragover, col))
+        col.on('dragleave', partial(on_dragleave, col))
+        col.on('drop', partial(on_drop, col, name))
+        return col
+
+    def make_draggable_card(todo: ToDo) -> ui.card:
+        card = ui.card().props('draggable').classes('w-full cursor-pointer bg-grey-1')
+        with card:
+            ui.label(todo.title)
+        card.on('dragstart', partial(on_dragstart, card, todo))
+        return card
+
+    def on_dragstart(card: ui.card, todo: ToDo) -> None:
+        app.storage.tab['dragging-todo'] = (card, todo)
+
+    def on_dragover(col: ui.column) -> None:
+        col.classes(remove='bg-blue-grey-2', add='bg-blue-grey-3')
+
+    def on_dragleave(col: ui.column) -> None:
+        col.classes(remove='bg-blue-grey-3', add='bg-blue-grey-2')
+
+    async def on_drop(tgt_col: ui.column, col_name: str) -> None:
+        dragging: Optional[Tuple[ui.card, ToDo]] = app.storage.tab.get(
+            'dragging-todo', None
+        )
+        if not dragging:
+            return
+        (card, todo) = dragging
+        del app.storage.tab['dragging-todo']
+        tgt_col.classes(remove='bg-blue-grey-3', add='bg-blue-grey-2')
+        if not card.parent_slot:
+            return
+        src_col = card.parent_slot.parent
+        if tgt_col == src_col:
+            # no change, nothing to do
+            return
+        src_skel = ui.skeleton().classes('w-full')
+        if False:
+            # This might benefit from a new ui.column.replace(old_element, new_element)
+            src_col.replace(card, src_skel)
+        else:
+            src_idx = card.parent_slot.children.index(card)
+            src_skel.move(src_col, src_idx)
+            card.parent_slot.children.remove(card)
+        tgt_skel = ui.skeleton().classes('w-full')
+        tgt_skel.move(tgt_col)
+
+        await asyncio.sleep(1.0)
+
+        src_col.remove(src_skel)
+        if False:
+            # This might benefit from a new ui.column.replace(old_element, new_element)
+            tgt_col.replace(tgt_skel, card)
+        else:
+            tgt_idx = tgt_col.default_slot.children.index(tgt_skel)
+            tgt_col.remove(tgt_skel)
+            tgt_col.default_slot.children.insert(tgt_idx, card)
+            card.parent_slot = tgt_col.default_slot
+        ui.notify(f'"{todo.title}" is now in {col_name}')
+
+    with ui.row():
+        with make_droppable_column('Next'):
+            make_draggable_card(ToDo('Provide Deployment'))
+        with make_droppable_column('Doing'):
+            make_draggable_card(ToDo('Improve Documentation'))
+        with make_droppable_column('Done'):
+            make_draggable_card(ToDo('Invent NiceGUI'))
+            make_draggable_card(ToDo('Test in own Projects'))
+            make_draggable_card(ToDo('Publish as Open Source'))
+            make_draggable_card(ToDo('Release Native-Mode'))
+
+
+ui.run()