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FletApp

Renders another Flet app in the current app, similar to HTML IFrame, but for Flet.

Inherits: LayoutControl

Properties

Events

  • on_connect - Fires when the client allocates an in-process dart_bridge channel for this embedded app (url="dartbridge://").
  • on_error - Called when a connection or any unhandled error occurs.
  • on_python_output - Fires once per stdout/stderr write inside the embedded Pyodide app.

Methods

  • wait_idle - Waits until the embedded app has rendered its UI and gone quiet.

Properties​

app_error_messageclass-attributeinstance-attribute​

app_error_message: str | None = None

Template message to display when the app fails to load. Use {message} placeholder to include the error message and {details} to include error details.

argsclass-attributeinstance-attribute​

args: dict[str, Any] | None = None

Optional dictionary of arguments to pass to the Flet app.

assets_dirclass-attributeinstance-attribute​

assets_dir: str | None = None

Base location for assets referenced by the embedded app. On web this is a URL prefix joined with relative src values (e.g. on Image/Lottie/Markdown); on desktop it is a filesystem path.

boot_screen_nameclass-attributeinstance-attribute​

boot_screen_name: str | None = None

Name of the boot screen to show while the embedded app starts up.

When None, the built-in "flet" boot screen is used. Custom boot screens are provided by extensions; see the boot screen docs.

boot_screen_optionsclass-attributeinstance-attribute​

boot_screen_options: dict[str, Any] | None = None

Options for the boot screen, passed through to the boot screen widget.

For the built-in "flet" screen these include spinner_size, startup_message, bgcolor_light/bgcolor_dark, etc. See the boot screen docs.

force_pyodideclass-attributeinstance-attribute​

force_pyodide: bool = False

Whether to force the use of Pyodide.

reconnect_interval_msclass-attributeinstance-attribute​

reconnect_interval_ms: int | None = None

Delay, in milliseconds, between reconnection attempts.

reconnect_timeout_msclass-attributeinstance-attribute​

reconnect_timeout_ms: int | None = None

Total time to try reconnecting.

urlclass-attributeinstance-attribute​

url: str | None = None

Flet app URL, e.g. http://localhost:8550 or flet.sock.

Events​

on_connectclass-attributeinstance-attribute​

on_connect: ControlEventHandler[FletApp] | None = None

Fires when the client allocates an in-process dart_bridge channel for this embedded app (url="dartbridge://"). The event data is the Dart native port the host must serve with a FletDartBridgeServer so the embedded app connects over it instead of a socket.

Advanced / embedder use — hosts that run another Flet program in-process (e.g. a gallery or preview) start their server on this port in the handler.

on_errorclass-attributeinstance-attribute​

on_error: ControlEventHandler[FletApp] | None = None

Called when a connection or any unhandled error occurs.

on_python_outputclass-attributeinstance-attribute​

on_python_output: (
    EventHandler[FletAppOutputEvent] | None
) = None

Fires once per stdout/stderr write inside the embedded Pyodide app. Pyodide line-buffers by default, so each event is typically one print(...) call. Only fires for embedded FletApps with force_pyodide=True; root-level Pyodide pages have nowhere to bubble the event.

Methods​

wait_idleasync​

wait_idle(
    idle_ms: int = 300, timeout_ms: int = 30000
) -> dict[str, Any]

Waits until the embedded app has rendered its UI and gone quiet.

Useful for a host that needs to know when the embedded app is ready, e.g. before taking a screenshot of it or reading its output after a restart.

Parameters:

  • idle_ms (int, default: 300) - How long, in milliseconds, the embedded app must send no UI updates after its first one to count as idle.
  • timeout_ms (int, default: 30000) - Give up after this many milliseconds.

Returns:

  • dict[str, Any] - A dict with status and error. status is "idle" once the
  • dict[str, Any] - app sent at least one UI update, then none for idle_ms, and
  • dict[str, Any] - that update is on screen; "error" if the app failed to start
  • dict[str, Any] - or crashed (error holds the message; on_error fires as
  • dict[str, Any] - well); "timeout" if it didn't settle within timeout_ms, for
  • dict[str, Any] - example an app that updates continuously. A new call supersedes
  • dict[str, Any] - a pending one, which returns "timeout".