feat(android): JNI execution handle

src/webview/android/main_pipe.rs

@@ -161,6 +161,11 @@ impl MainPipe<'_> {
             Err(e) => tx.send(Err(e.into())).unwrap(),
           }
         }
+        WebViewMessage::Jni(f) => {
+          if let Some(webview) = &self.webview {
+            f(env, activity, webview.as_obj());
+          }
+        }
       }
     }
     Ok(())
@@ -188,12 +193,12 @@ fn set_background_color<'a>(
   Ok(())
 }
 
-#[derive(Debug)]
 pub enum WebViewMessage {
   CreateWebView(CreateWebViewAttributes),
   Eval(String),
   SetBackgroundColor(RGBA),
   GetWebViewVersion(Sender<Result<String, Error>>),
+  Jni(Box<dyn FnOnce(JNIEnv, JObject, JObject) + Send>),
 }
 
 #[derive(Debug)]

src/webview/android/mod.rs

@@ -242,6 +242,20 @@ impl InnerWebView {
   }
 }
 
+#[derive(Clone, Copy)]
+pub struct JniHandle;
+
+impl JniHandle {
+  /// Execute jni code on the thread of the webview.
+  /// Provided function will be provided with the jni evironment, Android activity and WebView
+  pub fn exec<F>(&self, func: F)
+  where
+    F: FnOnce(JNIEnv, JObject, JObject) + Send + 'static,
+  {
+    MainPipe::send(WebViewMessage::Jni(Box::new(func)));
+  }
+}
+
 pub fn platform_webview_version() -> Result<String> {
   let (tx, rx) = bounded(1);
   MainPipe::send(WebViewMessage::GetWebViewVersion(tx));

src/webview/mod.rs

@@ -15,6 +15,8 @@ pub mod prelude {
   pub use super::android::{binding::*, setup};
 }
 #[cfg(target_os = "android")]
+pub use android::JniHandle;
+#[cfg(target_os = "android")]
 use android::*;
 #[cfg(any(
   target_os = "linux",
@@ -662,6 +664,19 @@ impl WebviewExtMacOS for WebView {
   }
 }
 
+#[cfg(target_os = "android")]
+/// Additional methods on `WebView` that are specific to Android
+pub trait WebviewExtAndroid {
+  fn handle(&self) -> JniHandle;
+}
+
+#[cfg(target_os = "android")]
+impl WebviewExtAndroid for WebView {
+  fn handle(&self) -> JniHandle {
+    JniHandle
+  }
+}
+
 #[cfg(test)]
 mod tests {
   use super::*;