slint-ui/slint · error

platform already initialized

Error message

platform already initialized

What it means

Error "platform already initialized" thrown in slint-ui/slint.

Source

Thrown at internal/backends/testing/lib.rs:45

pub mod systest;

/// Initialize the testing backend without support for event loop.
/// This means that each test thread can use its own backend, but global functions that needs
/// an event loop such as `slint::invoke_from_event_loop` or `Timer`s won't work.
/// Must be called before any call that would otherwise initialize the rendering backend.
/// Calling it when the rendering backend is already initialized will panic.
///
/// Note that for animations and timers, the changes in the system time will be disregarded.
/// Instead, use [`mock_elapsed_time()`] to advance the simulate (mock) time Slint uses.
pub fn init_no_event_loop() {
    i_slint_core::platform::set_platform(Box::new(testing_backend::TestingBackend::new(
        testing_backend::TestingBackendOptions {
            mock_time: true,
            threading: false,
            ..Default::default()
        },
    )))
    .expect("platform already initialized");
}

/// Initialize the testing backend with support for simple event loop.
/// This function can only be called once per process, so make sure to use integration
/// tests with only one `#[test]` function. (Or in a doc test)
/// Must be called before any call that would otherwise initialize the rendering backend.
/// Calling it when the rendering backend is already initialized will panic.
///
/// Note that for animations and timers, the changes in the system time will be disregarded.
/// Instead, use [`mock_elapsed_time()`] to advance the simulate (mock) time Slint uses.
pub fn init_integration_test_with_mock_time() {
    i_slint_core::platform::set_platform(Box::new(testing_backend::TestingBackend::new(
        testing_backend::TestingBackendOptions {
            mock_time: true,
            threading: true,
            ..Default::default()
        },
    )))

View on GitHub (pinned to 3fd8f2ec03)

Solutions

1. Initialize the testing platform only once per process.
2. Guard initialization with a once flag in test setup.

When it happens

Trigger: Thrown at internal/backends/testing/lib.rs:45 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of slint-ui/slint@3fd8f2ec03 (2026-08-19). Data as JSON: /api/errors/d7c109bb9f8bf2cc. Report an issue: GitHub.