Retrieve the Java instance of the Android activity class.
Defined in <SDL3/SDL_system.h>
void * SDL_GetAndroidActivity(void);(void *) Returns the jobject representing the instance of the Activity class of the Android application, or NULL on failure; call SDL_GetError() for more information.
The prototype of the function in SDL's code actually declares a void* return type, even if the implementation returns a jobject. The rationale being that the SDL headers can avoid including jni.h.
The jobject returned by the function is a local reference and must be released by the caller. See the PushLocalFrame() and PopLocalFrame() or DeleteLocalRef() functions of the Java native interface:
https://docs.oracle.com/javase/1.5.0/docs/guide/jni/spec/functions.html
It is safe to call this function from any thread.
This function is available since SDL 3.0.0.
#include <SDL3/SDL.h>
#include <jni.h>
// This example requires C++ and a custom Java method named "void showHome()"
// Calls the void showHome() method of the Java instance of the activity.
void showHome(void)
{
// retrieve the JNI environment.
JNIEnv* env = (JNIEnv*)SDL_GetAndroidJNIEnv();
// retrieve the Java instance of the SDLActivity
jobject activity = (jobject)SDL_GetAndroidActivity();
// find the Java class of the activity. It should be SDLActivity or a subclass of it.
jclass clazz(env->GetObjectClass(activity));
// find the identifier of the method to call
jmethodID method_id = env->GetMethodID(clazz, "showHome", "()V");
// effectively call the Java method
env->CallVoidMethod(activity, method_id);
// clean up the local references.
env->DeleteLocalRef(activity);
env->DeleteLocalRef(clazz);
// Warning (and discussion of implementation details of SDL for Android):
// Local references are automatically deleted if a native function called
// from Java side returns. For SDL this native function is main() itself.
// Therefore references need to be manually deleted because otherwise the
// references will first be cleaned if main() returns (application exit).
}