Add session_on_end example

Author: schloerke

shiny/api-examples/session_on_end/app.py

@@ -0,0 +1,53 @@
+from starlette.requests import Request
+
+from shiny import App, Inputs, Outputs, Session, reactive, render, ui
+from shiny.bookmark import BookmarkState
+
+
+# App UI **must** be a function to ensure that each user restores their own UI values.
+def app_ui(request: Request):
+    return ui.page_fluid(
+        ui.markdown(
+            "Directions: "
+            "\n1. Change the radio buttons below"
+            "\n2. Changing the radio button will cause a server error."
+            "\n3. The app will save the state to the URL before disconnecting."
+            "\n4. Refresh, your browser. The radio button selection should persist."
+        ),
+        ui.hr(),
+        ui.input_radio_buttons(
+            "letter",
+            "Pick a letter",
+            choices=["A", "B", "C"],
+        ),
+        "Selection:",
+        ui.output_code("letter_out"),
+    )
+
+
+def server(input: Inputs, output: Outputs, session: Session):
+
+    @render.code
+    def letter_out():
+        return input.letter()
+
+    @reactive.effect
+    @reactive.event(input.letter, ignore_init=True)
+    async def _():
+        # Simulate a server error when the radio button is changed
+        raise RuntimeError("Simulated server error")
+
+    # When the session ends, update the query string with the latest bookmark information
+    @session.on_end
+    async def _():
+        await session.bookmark.update_query_string()
+
+    # Reset query string when restoring state
+    @session.bookmark.on_restored
+    async def _(state: BookmarkState):
+        await session.bookmark.update_query_string(session.clientdata.url_pathname())
+
+
+# Make sure to set the bookmark_store to `"url"` (or `"server"`)
+# to store the bookmark information/key in the URL query string.
+app = App(app_ui, server, bookmark_store="url")

shiny/session/_session.py

@@ -211,6 +211,7 @@ async def close(self, code: int = 1001) -> None:
     @abstractmethod
     def _is_hidden(self, name: str) -> bool: ...
 
+    @add_example("session_on_end")
     @abstractmethod
     def on_end(
         self,