The #GAppLaunchContext::launch-started signal is emitted when a #GAppInfo is
about to be launched. If non-null the @platform_data is an
GVariant dictionary mapping strings to variants (ie a{sv}), which
contains additional, platform-specific data about this launch. On
UNIX, at least the startup-notification-id keys will be
present.
The #GAppLaunchContext::launch-started signal is emitted when a #GAppInfo is about to be launched. If non-null the @platform_data is an GVariant dictionary mapping strings to variants (ie a{sv}), which contains additional, platform-specific data about this launch. On UNIX, at least the startup-notification-id keys will be present.
The value of the startup-notification-id key (type s) is a startup notification ID corresponding to the format from the [startup-notification specification](https://specifications.freedesktop.org/startup-notification-spec/startup-notification-0.1.txt). It allows tracking the progress of the launchee through startup.
It is guaranteed that this signal is followed by either a #GAppLaunchContext::launched or #GAppLaunchContext::launch-failed signal.