robius-android-env 0.2.0

Rust access to Android state (native Java objects) managed by UI toolkits
Documentation 
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//! The implementation for UI toolkits that work with [ndk-context].
//!
//! This module works by accessing the [`AndroidContext`] state stored in [ndk-context],
//! which must be initialized by other crates (e.g., `android-activity`).
//! before this module uses those states.
//!
//! [ndk-context]: https://docs.rs/ndk-context/latest/ndk_context/
//! [`AndroidContext`]: https://docs.rs/ndk-context/latest/ndk_context/struct.AndroidContext.html

use crate::{JavaVM, JNIEnv, JObject};

pub fn with_activity_inner<F, R>(f: F) -> crate::Result<R>
where
    F: for<'a, 'b, 'c, 'd> FnOnce(&'a mut JNIEnv<'b>, &'c JObject<'d>) -> R,
{
    let android_context = ndk_context::android_context();
    // SAFETY: we have no option but to trust the pointers from ndk-context.
    let (vm, activity) = unsafe { (
        JavaVM::from_raw(android_context.vm().cast())?,
        JObject::from_raw(android_context.context().cast()),
    )};

    let mut env = vm.attach_current_thread_permanently()?;
    Ok(f(&mut env, &activity))
}