listen() handler not being called at first? | Tauri Apps | Page 1

harsh pewter Dec 31, 2023, 5:04 PM

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The JS below calls listen() then init_page(), which calls the initialize_view() command, which emit()s an update_vm event, but the listen()ing handler does not get called. This first event is meant to hydrate the page. Apparently the event is not delivered.

Clicking a button causes a (different) command to be called, which then emit()s the same update_vm event, which is delivered.

This surprises me... what am I missing?

Thanks!!!

JS:

listen('update_view', handle__update_view__event);
console.log("listen()ed");

//...

function init_page() {
  invoke('initialize_view');
  document.body.style.display = "block";
}

if (document.readyState != "loading") {
  init_page();
} else {
  window.addEventListener("DOMContentLoaded", init_page);
}

main.rs:

fn update_view(window: &Window, vm: &ViewModel) {
    eprintln!("update_view(vm: {vm:?})");
    window.emit("update_view", &vm).expect("emit(update_view) failed");
}

fn mut_vm<F>(window: &Window, vm: &Arc<Mutex<ViewModel>>, f: F)
    where F: FnOnce(&mut ViewModel)
{
    let mut guarded_vm = vm.lock().expect("vm.lock() failed");
    f(guarded_vm.deref_mut());
    update_view(&window, &*guarded_vm);
}

#[tauri::command]
fn initialize_view(window: Window, vm: State<Arc<Mutex<ViewModel>>>) {
    println!("initialize_view()");
    mut_vm(&window, &vm, |vm| vm.app_state = AppState::MainPage); // TODO: remove, just emit the event
}

Console output:

 
tauri://localhost/main.js:44:12: CONSOLE LOG listen()ed
initialize_view()
update_view(vm: ViewModel { app_state: MainPage, pedal_connected: false, drive_connected: false })
    <==== should see '... CONSOLE LOG handle__update_view__event'

After clicking a button:

update_view(vm: ViewModel { app_state: StartPage, pedal_connected: false, drive_connected: false })
tauri://localhost/view_interface.js:156:14: CONSOLE LOG handle__update_view__event
... more logging as the page is hydrated ...

#

Here's main(), for reference (posted here to keep post short):

📎 message.txt

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listen() handler not being called at first?

native cosmos Dec 31, 2023, 8:29 PM

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Since it looks like you're targeting a specific window for events, have you tried appWindow.listen or getCurrent().listen instead of global listens? I know this confused me as well.

lament eagle Dec 31, 2023, 8:35 PM

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Another thing to try is to await listen() since it is a Promise.

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Of course the handler should still run regardless, but sometimes there is a cleanup (explicit or implicit) that happens before it receives an event.

harsh pewter Dec 31, 2023, 10:46 PM

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native cosmos Since it looks like you're targeting a specific window for events, have you trie...

Both windows listen(``update_vm``, ...), as it happens. Are you saying that appWindow.listen() or getCurrent().listen() are more reliable in some way?

harsh pewter Dec 31, 2023, 10:49 PM

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lament eagle Another thing to try is to `await listen()` since it is a Promise.

This did the trick. Apparently, I was just getting lucky when it worked w/out the await.

Many thanks!

lament eagle Dec 31, 2023, 10:51 PM

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harsh pewter This did the trick. Apparently, I was just getting lucky when it worked w/out th...

No problem! Async stuff in JS has too many footguns, I think. 😄

harsh pewter Dec 31, 2023, 10:51 PM

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Plus, I'm a newbie to this, so I didn't notice the async nature.

#listen() handler not being called at first?