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docs/skills/nicegui-ui-customization/references/interaction-patterns.md

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+# Interaction Patterns Reference
+
+## Reactive State
+
+Use bindable dataclasses for local page state.
+
+```python
+from dataclasses import field
+from nicegui import binding, ui
+
+@binding.bindable_dataclass
+class PageState:
+    selected_id: int | None = None
+    items: list = field(default_factory=list)
+
+state = PageState()
+ui.label().bind_text_from(state, "selected_id")
+```
+
+## File Upload Pattern
+
+- Validate extension and size before storing.
+- Delegate storage to a service method.
+- Notify success and failure explicitly.
+
+```python
+async def handle_upload(e: ui.events.UploadEventArguments):
+    try:
+        if e.size > 10 * 1024 * 1024:
+            raise ValueError("File too large")
+        if not e.name.endswith(".pdf"):
+            raise ValueError("Only PDF allowed")
+        await file_service.store(e.content.read(), e.name)
+        ui.notify(f"Uploaded: {e.name}", type="positive")
+    except ValueError as err:
+        ui.notify(str(err), type="negative")
+
+ui.upload(on_upload=handle_upload, auto_upload=True)
+```
+
+## Form Submission Pattern
+
+- Bind UI inputs to dataclass fields.
+- Perform validation in the service layer.
+- Clear form state on success.
+
+```python
+@binding.bindable_dataclass
+class FormData:
+    name: str = ""
+    email: str = ""
+
+data = FormData()
+ui.input("Name").bind_value(data, "name")
+ui.input("Email").bind_value(data, "email")
+
+async def on_submit():
+    try:
+        await user_service.create_user(name=data.name, email=data.email)
+        ui.notify("User created", type="positive")
+        data.name = data.email = ""
+    except ValueError as err:
+        ui.notify(str(err), type="negative")
+
+ui.button("Submit").on_click(on_submit)
+```
+
+## Real-Time Updates Decision
+
+Use SSE for one-way status streaming.
+Use WebSocket for bidirectional messaging.
+
+SSE endpoint example:
+
+```python
+@app.get("/events/status")
+async def status_stream():
+    async def gen():
+        while True:
+            yield f"data: {await get_status()}\\n\\n"
+            await asyncio.sleep(1)
+    return StreamingResponse(gen(), media_type="text/event-stream")
+```
+
+## Background Work Pattern
+
+- Start long jobs in FastAPI background tasks.
+- Expose status via endpoint or streaming channel.
+- Guard buttons against duplicate submissions during in-flight tasks.
+
+## Explicit Refresh Pattern
+
+Use @ui.refreshable and call refresh intentionally instead of polling unrelated state.
+
+```python
+@ui.refreshable
+async def item_list():
+    items = await service.list()
+    for item in items:
+        ui.label(item.name)
+
+ui.button("Refresh").on_click(lambda: item_list.refresh())
+```
+
+## Links
+
+- NiceGUI action events: https://nicegui.io/documentation/section_action_events
+- FastAPI SSE: https://fastapi.tiangolo.com/advanced/server-sent-events/
+- FastAPI WebSockets: https://fastapi.tiangolo.com/advanced/websockets/