How do I get &AppHandle instance in “extern "system" fn”so that I can emit message to js?

[weartist]

I'm using windows api that listens to mouse and keyboard, like "SetWindowsHookExA" but this api needs a function address for callbacks, is there any way I can get AppHandle in one function? If there is a global reference to it, I searched the documentation but couldn't find the corresponding method, thanks a lot

[FabianLars]

I'd suggest looking into the once_cell crate. You could move an AppHandle from tauri's setup hook (the earliest point in time where you can get an AppHandle) into a OnceCell and access it similar to a global variable.

[wtto00]

I use once_cell like this:

// Declare global static variable
static APP_HANDLE: OnceCell<Mutex<AppHandle>> = OnceCell::new();

// Set APP_HANDLE
APP_HANDLE
  .set(Mutex::new(app.app_handle().to_owned()))
  .unwrap();

// Get APP_HANDLE
let app = APP_HANDLE.get().unwrap().lock();
if let Ok(app_handle) = app {
    app_handle
        .emit_all("plugin:iap|exception", ExceptionError { code, message })
        .unwrap();
}

To set APP_HANDLE, I had to remove <R: Runtime> in pub fn init<R: Runtime>() -> TauriPlugin<R>, and changed it to pub fn init() -> TauriPlugin<Wry>.

[merlindru]

From the other comments, here's how I did it with Tauri v2

use std::sync::OnceLock; // OnceLock is part of std now

static APP_HANDLE: OnceLock<AppHandle> = OnceLock::new();

#[cfg_attr(mobile, tauri::mobile_entry_point)]
pub fn run() {
    let context = tauri::generate_context!();

    let app = tauri::Builder::default()
        // config omitted for brevity
        .build(context)
        .unwrap();

    APP_HANDLE.set(app.app_handle().to_owned()).unwrap();

    app.run(|_, _| {});
}

Then I made a small helper function to use it:

fn app_handle<'a>() -> &'a AppHandle {
    APP_HANDLE.get().unwrap()
}

// Enjoy:
fn foo() {
  let app_handle = app_handle();
}